Volume 1 of 4 Filed November 2, 1999 UNITED STATES COURT OF APPEALS FOR THE THIRD CIRCUIT Nos. 96-7623/7624/7625 IN RE: TMI LITIGATION LORI DOLAN; JOSEPH GAUGHAN; RONALD WARD; ESTATE OF PEARL HICKERNELL; KENNETH PUTT; ESTATE OF ETHELDA HILT; PAULA OBERCASH; JOLENE PETERSON; ESTATE OF GARY VILLELLA; ESTATE OF LEO BEAM, Appellants No. 96-7623 IN RE: TMI LITIGATION ALL PLAINTIFFS EXCEPT LORI DOLAN, JOSEPH GAUGHAN, RONALD WARD, ESTATE OF PEARL HICKERNELL, KENNETH PUTT, ESTATE OF ETHELDA HILT, PAULA OBERCASH, JOLENE PETERSON, ESTATE OF GARY VILLELLA AND ESTATE OF LEO BEAM, Appellants No. 96-7624 IN RE: TMI LITIGATION ALL PLAINTIFFS; ARNOLD LEVIN; LAURENCE BERMAN; LEE SWARTZ Appellants No. 96-7625 ON APPEAL FROM THE UNITED STATES DISTRICT COURT FOR THE MIDDLE DISTRICT OF PENNSYLVANIA (Civil No. 88-cv-01452) (District Judge: Honorable Sylvia H. Rambo)  ARGUED: June 27, 1997 Before: GREENBERG and McKEE, Circuit Judges, and GREENAWAY, District Judge* (Opinion filed: November 2, 1999) ARNOLD LEVIN, ESQ. LAURENCE S. BERMAN, ESQ. (Argued) CRAIG D. GINSBURG, ESQ. Levin, Fishbein, Sedran & Berman 510 Walnut Street, Suite 500 Philadelphia, PA 19106 LEE C. SWARTZ, ESQ. Hepford, Swartz & Morgan 111 North Front Street P.O. Box 889 Harrisburg, PA 17108 Attorneys for Appellants in No. 96-7623/7624/7625 LOU TARASI, ESQ. Tarasi & Johnson, P.C. 510 Third Avenue Pittsburgh, PA 15129 Of Counsel for Certain Appellants Identified in the Entry of Appearance in Appeal No. 96-7624/7625 _________________________________________________________________ * The Honorable Joseph A. Greenaway, Jr., United States District Court Judge for the District of New Jersey, sitting by designation. 2  STEPHEN A. SALTZBURG, ESQ. (Argued) Howrey Professor of Trial Advocacy, Litigation and Professional Responsibility George Washington Law School 720 20th Street, N.W. Washington, D.C. 20052 Of Counsel for Appellants in No. 96-7623/7624/7625 DANIEL J. CAPRA, ESQ. Reed Professor of Law Fordham University School of Law Lincoln Center 140 West 62nd Street New York, NY 10023 Of Counsel for Certain Appellants Identified in the Entry of Appearance in Appeal No. 96-7625 A.H. WILCOX, ESQ. (Argued) ELLEN K. SCOTT, ESQ. (Argued) ERIC J. ROTHSCHILD, ESQ. (Argued) Pepper, Hamilton & Scheetz, LLP 3000 Two Logan Square 18th and Arch Streets Philadelphia, PA 19103 LEWIS S. KUNKEL, JR., ESQ. THOMAS B. SCHMIDT, III, ESQ. Pepper, Hamilton & Scheetz LLP 200 One Keystone Plaza North Front & Market Streets P.O. Box 1181 Harrisburg, PA 17108 Attorneys for Appellees in Nos. 96-7623/7624/7625 3  REUBEN A. GUTTMAN, ESQ. Provost & Umphrey 1350 New York Avenue, N.W. Suite 1040 Washington, D.C. 20005 NED MILTENBERG, ESQ. Associate General Counsel Association of Trial Lawyers of America ("ATLA") 1050 31st Street, N.W. Washington, D.C. 20007 Amicus Curiae, Association of Trial Lawyers of America ("ATLA"), in Support of Appellants TABLE OF CONTENTS I. INTRODUCTION 6 II. PROCEDURAL HISTORY 8 III. SCIENTIFIC BACKGROUND 18 A. Overview of Relevant Principles of Nuclear Physics 18 1. Atomic and Nuclear Structure 18 2. Radioactivity 24 3. Ionizing Radiation 28 4. Radiation Quantities and Units 31 5. Health Effects of Ionizing Radiation 35 i. Deterministic Effects 38 ii. Stochastic Effects 41 6. Radiation in the Environment 44 i. Natural Radiation 44 ii. Man-made Radiation 49 IV. NUCLEAR ENGINEERING 54 A. Nuclear Reaction 54 B. The Operation of Nuclear Power Plant 59 C. Barriers to Release of Radioactive Materials into the Environment 65 4  V. THE ACCIDENT AND ITS AFTERMATH 66 A. The Accident at TMI-2 66 B. Radioactive Materials Released to the Environment 70 C. Pathways of Exposure to Radioactive Materia ls 71 VI. LEGAL DISCUSSION 72 A. The Trial Plaintiffs' Appeal 72 1. Background 72 2. Standards Governing the Admissibility of Scientific Evidence 79 3. Trial Plaintiffs' Dose Exposure Expert Witnesses 85 i. Ignaz Vergeiner 85 a. Qualifications 85 b. Vergeiner's Opinion. 86 c. Discussion and Conclusions 87 ii. Charles Armentrout and Victor Neuwirth 95 a. Qualifications 95 b. Armentrout's Observations and Experiences 96 c. Discussion and Conclusion 98 d. Neuwirth's Soil Sample Analyses and Armentrout's Dose Estimates. 99 e. Discussion and Conclusion 101 iii. James Gunckel 105 a. Qualifications 105 b. Gunckel's Opinion 108 c. Discussion and Conclusions 112 iv. Vladimir Shevchenko 118 a. Qualifications 118 b. Shevchenko's Tree Study 120 c. Discussion and Conclusions 123 d. The Cytogenetic Analysis 126 e. Discussion and Conclusions 130 v. Gennady Kozubov 135 a. Qualifications 135 b. Kozubov's Opinion 135 c. Discussion and Conclusions 137 vi. Olga Tarasenko 139 a. Qualifications 139 b. Tarasenko's Opinion 140 5  c. Discussion and Conclusions 142 vii. Bruce Molholt 145 a. Qualifications 145 b. Molholt's Opinions 146 c. Discussion and Conclusions 149 viii. Sigmund Zakrzewski 155 a. Qualifications 155 b. Zakrzewski's Opinion 158 c. Discussion and Conclusions 159 ix. Theodor Sterling 161 a. Qualifications 161 b. Sterling's Opinion 161 c. Discussion and Conclusions 163 x. Steven Wing 166 a. Qualifications 166 b. Wing's Mortality Study 166 c. Discussion and Conclusions 168 d. Wing's Cancer Incidence Study 170 e. Discussion and Conclusions 173 xi. Douglas Crawford-Brown 173 a. Qualifications 175 b. Crawford-Brown's Opinion 175 c. Discussion and Conclusions 176 4. Effect of the Exclusion of Wing's Lung Cancer Testimony 179 5. Exclusion of Experts' Submissions as Untimely 181 6. Conclusion 190 B. The Non-Trial Plaintiffs' Appeal 191 C. The Monetary Sanctions Appeal 200 D. Reassignment Upon Remand 201 VII. CONCLUSION 203 OPINION OF THE COURT McKEE, Circuit Judge I. INTRODUCTION These three appeals arise out of the nuclear reactor 6  accident which occurred on March 28, 1979, at Three Mile Island in Dauphin County, Pennsylvania.1 Two of the appeals concern the personal injury claims of more than 2,000 Three Mile Island area residents who allege that they have developed neoplasms2 as a result of the radiation released into the environment as a result of the reactor accident. The first appeal is that of a group of ten trial plaintiffs who were selected by the parties after the District Court adopted the plaintiffs' case management order, which called for a "mini-trial" of the claims of a group of "typical" plaintiffs (the "Trial Plaintiffs"). The critical issue there is the trial plaintiffs' ability to demonstrate that they were exposed to doses of radiation sufficient to cause their neoplasms. Proof of that causation depended on the admissibility of the testimony of several experts that the Trial Plaintiffs retained. These experts attempted to testify about the amount of radiation released into the environment by the nuclear reactor accident, and thereby correlate the plaintiffs' neoplasms to that accident. Defendants challenged the admissibility of the experts' testimony and the District Court was therefore required to hold extensive in limine hearings pursuant to its "gatekeeping" role under Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993). Following those hearings, the court excluded the overwhelming majority of the Trial Plaintiffs' proposed expert testimony as to dose exposure. Following the exclusion of the dose exposure _________________________________________________________________ 1. Sometime prior to argument, the appellees moved to consolidate these appeals. We denied that request by order dated December 24, 1996. We did, however, instruct the Clerk to list these three appeals before a single merits panel. We now believe that the most expeditious way to dispose of these appeals is to consolidate them and dispose of them in one opinion. Therefore, we have entered an order consolidating these three appeals. 2. A neoplasm is "an abnormal tissue that grows by cellular proliferation more rapidly than normal and continues to grow after the stimuli that initiated the new growth cease. N[eoplasm]s show partial or complete lack of structural organization and functional coordination with the normal tissue, and usually form a distinct mass of tissue which may be either benign or malignant." STEDMAN'S MEDICAL DICTIONARY 931 (26th ed. 1995). 7  testimony, the defendants moved for summary judgment alleging that Trial Plaintiffs could not establish causation absent the excluded expert testimony regarding dose. The District Court agreed and held that, as a result of its rulings under Daubert, Trial Plaintiffs were unable to connect their neoplasms to the TMI accident. Accordingly, the court granted summary judgment in favor of defendants and against the Trial Plaintiffs. In re TMI Litigation Consolidated Proceedings, 927 F. Supp. 834 (M.D. Pa. 1996). The District Court then reasoned that its Daubert rulings would be binding on all of the other plaintiffs, i.e., the Non-Trial Plaintiffs, if there were evidentiary issues common to all plaintiffs, Id. at 837. Therefore, the court therefore extended its Trial Plaintiff summary judgment decision to the Non-Trial Plaintiffs, and granted summary judgment to the defendants on all of the claims of the approximately 2,000 remaining TMI personal injury plaintiffs. The propriety of that extension is the subject of the second appeal. The third and last appeal concerns the propriety of the District Court's imposition of monetary sanctions against certain of the plaintiffs' counsel for violations of pre-trial discovery requirements and orders. The sanctioned counsel have requested that the TMI personal injury litigation be reassigned to another trial judge upon remand, if we reverse the District Court in either or both of thefirst two appeals. For the reasons that follow, we will affirm the grant of summary judgment to the defendants on the claims of the Trial Plaintiffs (No. 96-7623). We will, however, reverse the grant of summary judgment to the defendants on the claims of the Non-Trial Plaintiffs (No. 96-7624), but we will affirm the imposition of monetary sanctions and deny the request for reassignment (No. 96-7625). II. PROCEDURAL HISTORY3 _________________________________________________________________ 3. The procedural history of this litigation is almost as complicated as the scientific principles implicated by the Daubert challenges that we discuss below. However, an understanding of the procedural history is necessary to our discussion of the District Court's decision to grant summary judgment against the Non-Trial Plaintiffs as well as the Trial Plaintiffs. 8  On March 28, 1979, radioactive materials were released into the environment as the result of an accident which occurred at Unit 2 of the Three Mile Island nuclear power generating station in Dauphin County ("TMI-2"). Three Mile Island is a small island in the Susquehanna River, approximately fifteen miles downstream from Harrisburg, Pennsylvania. Following the accident, thousands of personal injury and other non-personal injury claims 4 were filed against the owners and operators of the nuclear facility.5 As noted, more than 2,000 plaintiffs filed claims for personal injuries6 purportedly caused by exposure to the radioactive materials released during the accident. Some of these personal injury claims were originally filed in the early 1980's in state and federal district courts in Pennsylvania, New Jersey and Mississippi. The defendants removed the state court actions to federal district courts in Pennsylvania and New Jersey, under the authority of the Price-Anderson Act, Pub.L. No. 85-256, 71 Stat. 576 (1957).7 _________________________________________________________________ 4. The defendants have settled non-personal injury claims brought by individuals, businesses and non-profit organizations within a twenty-five mile radius of the TMI facility. See Stibitz v. General Public Utility Corp., 746 F.2d 993, 995 n.1 (3d Cir. 1984). 5. The defendants are General Public Utilities, Inc., Metropolitan Edison Co., Jersey Central Power & Light Co., Pennsylvania Electric Co., Babcock & Wilcox, Co., McDermott Inc., Raytheon Constructors, Inc., and Burns & Roe Enterprises, Inc. They were, at the time of the accident, either the owners and operators of the facility or companies which had provided design, engineering and/or maintenance services to the owners and operators or vendors of equipment or systems installed in the facility. In re TMI Litigation Cases Consol. II, 940 F.2d 832, 836 (3d Cir. 1991). 6. The personal injury plaintiffs allege that they have developed radiation induced neoplasms because of their exposure to ionizing radiation resulting from the TMI accident. 7. As we noted in In re TMI Litigation Cases Consolidated II, 940 F.2d 832, 837 n.2 (3d Cir. 1991), the Price-Anderson Act was enacted in 1957 as an amendment to the Atomic Energy Act of 1946, Pub.L. No. 79-585, 60 Stat. 755. The Atomic Energy Act was designed to establish an industry to generate inexpensive electrical power and it envisioned turning "atomic power into a source of energy" by turning "swords into plowshares." Pacific Gas & Electric Co. v. State Energy Resources 9  After removal, the District Court for the Middle District of Pennsylvania ordered, inter alia, that all pending TMI personal injury cases in the Middle District be "consolidated for pretrial proceedings only." App. 13097. The District Court also ordered that the caption of every subsequent personal injury pleading should be identified as a personal injury claim. Id. After we held that the Price-Anderson Act did not create a cause of action as a federal tort and was not intended to confer jurisdiction on federal district courts, see Stibitz v. General Public Utilities Corp., 746 F.2d 993, 997 (3d Cir. 1984) and Kiick v. Metropolitan Edison Co., 784 F.2d 490, _________________________________________________________________ Conservation & Development Commission, 461 U.S. 190, 193 (1983). The Atomic Energy Act envisioned the nuclear energy industry as a government monopoly; however, Congress ultimately decided to permit the private sector to become involved. See Atomic Energy Act of 1954, Pub.L. No. 830-703, 68 Stat. 919. The 1954 Act "grew out of Congress' determination that the national interest would best be served if the Government encouraged the private sector to become involved in the development of atomic energy for peaceful purposes under a program of federal regulation and licensing." Pacific Gas & Electric Co., 461 U.S. at 206-07. Nonetheless, the private sector was wary of the potential exposure it faced in the event of a nuclear accident because of the nature of nuclear energy. Thus, while assuring Congress that the risk of a major nuclear accident was low, "spokesmen for the private sector informed Congress that they would be forced to withdraw from the field if their liability were not limited by appropriate legislation." Duke Power Co. v. Carolina Environmental Study Group, Inc., 438 U.S. 59, 64 (1978). In response, Congress enacted the Price-Anderson Act to protect the public and encourage the development of the atomic energy industry. In re TMI, 67 F.3d 1103, 1107 (3d Cir. 1995)(citations and internal quotations omitted), cert. denied, #6D6D 6D# U.S. ___, 116 S. Ct. 1034 (1996). The Price-Anderson Act limited the "potential civil liability of nuclear power plant operators and provided federal funds to help pay damages caused by nuclear accidents." Id. The Act requires nuclear facilities operators to purchase a specified amount of insurance from private carriers and further provides for government indemnification above the insurance amounts to an established aggregate limit on liability. In re TMI Litigation Cases Consolidated II, 940 F.2d at 837 n.2. The Price- Anderson Act has been amended three times, most recently in 1988; yet the goal continues to be "to encourage private sector participation in the beneficial uses of nuclear materials." Id. at 853. 10  493 (3d Cir. 1986), the state court actions were remanded, and the federal court actions were transferred to the appropriate state courts. The cases originally removed to the Middle District of Pennsylvania, and those originally filed in the Middle District, were either remanded or transferred to the Court of Common Pleas of Dauphin County. Thereafter, in 1985 and 1986, the bulk of the personal injury claims which are the subject of this appeal were filed in the state courts.8 On October 15, 1985, the Dauphin County Common Pleas Court entered a case management order. In that order, the Court of Common Pleas ordered that all cases be consolidated for pretrial purposes, and also required that all pleadings be captioned to identify which plaintiffs' group they applied to. That is, all personal injury cases received from the federal court were consolidated under the caption "Cases Consolidated I" and the cases filed in state court after our decision in Stibitz, were consolidated under the caption "Cases Consolidated II." In 1988, Congress enacted the Price-Anderson Amendments Act of 1988, Pub.L. No. 100-408, 102 Stat. 1066. Those amendments to the Price-Anderson Act created a federal cause of action for "public liability actions"9 and provided that all such suits arise under the Price-Anderson Act, 42 U.S.C. S 2014(h). The Act also provided for consolidation of such actions, including those already filed, _________________________________________________________________ 8. However, personal injury cases continued to befiled after 1986. The last case filed that is included in these appeals was Kline, et al. v. General Public Utilities Corp. et al., No. 1:CV 96-451 (M.D. Pa.), and it was filed on March 15, 1996. However, the latest personal injury case filed is Tyler et al v. General Public Utilities Corp. et al., No. 1:CV 96-1028 (M.D. Pa.), and it was filed on June 7, 1996. Brief of Appellants in No. 96-7624, at 6 n.8. Apparently, Tyler is not included in this appeal. 9. The Price-Anderson Amendments Act defined a"public liability action" as "any suit asserting public liability." 42 U.S.C. S 2014(h). "Public liability" was defined as "any legal liability arising out of or resulting from a nuclear incident or precautionary evacuation," except for certain claims covered by workers' compensation, incurred in wartime or that involve the licensed property where the nuclear incident occurs. 42 U.S.C. S 2104(w). 11  in one federal district court. 42 U.S.C. S 2210(n).10 Following enactment of that Act, the defendants removed all the pending state actions to the United States District Court for the Middle District of Pennsylvania. Thereafter, the District Court for the Middle District of Pennsylvania conducted a case management conference. The personal injury cases known as "Cases Consolidated I" and "Cases Consolidated II" which had been removed from the Court of Common Pleas of Dauphin County were then pending in the Middle District along with the companion actions to the "Cases Consolidated II" which had been filed by forty-two plaintiffs in Mississippi federal and state court to take advantage of the more lenient Mississippi statute of limitations.11 As a result of discussions during the conference, the District Court entered an order which required counsel to meet to streamline the record with an eye toward reducing the number of duplicative plaintiffs and suits, assigning fewer case numbers for the various actions, and deciding which cases needed new complaints to be filed and which actions do not need answers filed. Supp. App. at 78. In response to the order, counsel for plaintiffs and defendants submitted a Stipulation which provided, inter alia, that the pending TMI personal injury cases referred to as "Cases Consolidated I" and "Cases Consolidated II," together with the companion Mississippi cases, would be consolidated under a single civil action number "for administrative purposes" (emphasis added). App. Vol. I, at 440. The Stipulation required that pleadings dealing with issues common to all plaintiffs, or a legal issue potentially applicable to all plaintiffs, bear the caption "In re TMI Consolidated Proceedings" as well as the additional _________________________________________________________________ 10. We subsequently upheld the constitutionality of the retroactive application of the federal jurisdiction provisions of the Price Anderson Amendments Act. In re TMI Litigation Cases Consolidated II, 940 F.2d 832 (3d Cir. 1991), cert. denied, 503 U.S. 906 (1992). 11. Counsel for the forty-two plaintiffs concede that they filed suit in Mississippi to take advantage of Mississippi's six-year statute of limitations. Pennsylvania had a two-year statute. In re TMI, 67 F.3d 1103, 1105 n.3 (3d Cir. 1995), cert. denied, 516 U.S. 1154 (1996). 12  legend: "This document Relates to: All Plaintiffs." Id. The Stipulation further required that pleadings dealing with issues relating to one or more identified plaintiffs be captioned "In Re TMI Consolidated Proceedings" and identify lead counsel, the number of plaintiffs represented by lead counsel and the number of plaintiffs to whom the pleadings refer. Id. The Stipulation also expressly provided that 3. Nothing in . . . this Stipulation . . . shal l be deemed to constitute or affect any waiver of claim, defense or issue, including but not limited to the statute of limitations, choice of law and bifurcation or consolidation for trial of claims, defenses, issues, parties or proceedings. Id. The Stipulation was subsequently approved by the District Court. Thereafter, in July of 1992, the defendants filed a motion for summary judgment directed to the forty-two plaintiffs who had sued in Mississippi state and federal courts. Defendants alleged that those claims were untimely under Section 11(b) of the Price-Anderson Amendments Act of 1988, codified at 42 U.S.C. S 2014(hh) (the choice of law provisions), which provides that "the substantive rules of decision in [any public liability action] shall be derived from the law of the State in which the nuclear incident involved occurs," and under Section 20(b) of that Act, (the effective date provision), which provides that "the amendments made by Section 11" of the Act "shall apply to nuclear incidents occurring before, on, or after the date of the enactment of this Act." 42 U.S.C. S 2014 note. The District Court ruled that the Mississippi actions were time-barred, dismissed the respective claims, and granted summary judgment in favor of the defendants because it reasoned thatS 20(b), read in conjunction with S 11, compelled the retroactive application of Pennsylvania's two-year statute of limitation to the plaintiffs' claims. In re TMI Cases Consolidated II, No. 88-14532, slip op. at 2-6 (M.D. Pa. Aug. 16, 1993). On appeal, the Mississippi plaintiffs argued, inter alia, that retroactive application of the choice of law provision violated constitutional guarantees of due process. We 13  disagreed, and held that the retroactive application of the choice of law provision was a rational exercise of Congress' legislative power. Accordingly, we affirmed the District Court's grant of summary judgment, and its dismissal of the claims of the forty-two plaintiffs. In re TMI, 89 F.3d 1106 (3d Cir. 1996), cert. denied, ___ U.S. ___, 117 S. Ct. 739 (1997). The defendants then moved for summary judgment against all the TMI plaintiffs, claiming that they had not breached the duty of care owed to the plaintiffs. The District Court denied the motion. The court held that state law on that issue was preempted, and that federal law determines the standard of care. In re TMI Litigation Cases Consolidated II, No. 88-1452, slip op. at 36 (M.D. Pa. Feb. 18, 1994). The court also held that federal regulations12 set the standard of care, and that each plaintiff must prove his or her individual exposure to radiation in order to establish causation, but not to establish a breach of the duty of care. Id. at 30-31. Upon defendants' motion, the District Court certified the duty of care and causation questions for interlocutory appeal.13 On that appeal, we held that plaintiffs must establish that (1) the defendants released radiation into the environment in excess of the levels permitted by the federal regulations in effect in 1979; (2) the plaintiffs were exposed to this radiation, although not necessarily at the levels prohibited by those regulations; (3) they have injuries; and (4) radiation was the cause of those injuries. In re TMI, 67 F.3d 1103, 1119 (3d Cir. 1995), cert. denied, 516 U.S. 1154 (1996). After remand, the District Court conducted lengthy in limine hearings in November of 1995 and in February and _________________________________________________________________ 12. See 10 C.F.R. SS 20.105, 20.106 (1979). These regulations were in effect at the time of the TMI accident. In re TMI, 67 F.3d 1103, 1108 n.10 (3d Cir. 1996), cert. denied, 516 U.S. 1154 (1996). However, the regulations have been significantly modified since then. Id. at 1111 n.19. 13. The District Court also certified a question concerning punitive damages. We held in a separate opinion that punitive damages are recoverable under the Price-Anderson Amendments Act of 1988 so long as the money to pay such award does not come from the United States Treasury. In re TMI, 67 F.3d 1119 (3d Cir. 1995), cert. denied, 517 U.S. 1163 (1996). 14  March of 1996, pursuant to Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993). Those hearings all relate to plaintiffs' radiation dose and medical causation expert witnesses. In January and April of 1996, the District Court issued several opinions granting the majority of the defendants' motions in limine. See In re TMI Cases Consolidated II, 166 F.R.D. 8 (M.D. Pa. 1996) (granting in part defendants' motions to exclude plaintiffs' medical causation experts); Id., 922 F. Supp. 1038 (M.D. Pa. 1996)(same); Id., 922 F. Supp. 997 (M.D. Pa. 1996) (granting in part defendants' motions to exclude plaintiffs' radiation dose and medical causation experts); Id., 911 F. Supp. 775 (M.D. Pa. 1996) (granting in part defendants' motions to exclude plaintiffs' radiation dose experts); Id., 910 F. Supp. 200 (M.D. Pa. 1996)(same). Although the District Court was convinced that the majority of the plaintiffs' expert witnesses were well-qualified, the court nonetheless "found many of their opinions to be based on methodologies that were scientifically unreliable and upon data that a reasonable expert in the field would not rely upon." In re TMI Litigation Consolidated Proceedings, 927 F. Supp. 834, 839 (M.D. Pa. 1996). Accordingly, it ruled that the much of the expert testimony was inadmissible under Daubert, and its progeny. In April of 1996, the defendants filed a motion for summary judgment. They based the motion upon their contention that the District Court's Daubert rulings left the plaintiff 's with no admissible evidence as to the radiation dose levels resulting from the TMI accident. A subsidiary issue arose during the summary judgment proceedings as to whom the summary judgment rulings would apply. That dispute had its beginnings in June of 1993, when the District Court adopted the plaintiffs' proposed case management plan which called for an"initial mini-trial of the claims of twelve `typical' plaintiffs," half chosen by plaintiffs and half chosen by defendants. App. at 168. Under the plaintiffs' plan (which was adopted by the District Court), discovery would proceed immediately as to all issues, including punitive damages and, upon completion of discovery, "the twelve illustrative Plaintiffs would then proceed to trial on all their claims." Id. 15  Ultimately, ten test plaintiffs,14 who have been diagnosed with the listed illnesses, were chosen.15 When the defendants filed their motion for summary judgment, they captioned it as pertaining to "All Plaintiffs" and argued that the District Court's summary judgment motion should be binding on all plaintiffs, not just the ten trial or test case plaintiffs. The District Court agreed, stating: The court finds that resolution of the issue before it turns on the grounds upon which the court ultimately grants or denies summary judgment. Defendants are correct that to the extent the ruling turns on broad evidentiary issues common to all Plaintiffs, the ruling will be binding on all Plaintiffs. Likewise, Plaintiffs are correct that insofar as a ruling is based on a more narrow, Plaintiff-specific inquiry, the ruling will apply only to certain Plaintiffs. The court's reading of documents related to the June 15, 1993 order, in conjunction with subsequent case management orders and evidentiary rulings, indicates that discovery and evidentiary matters were to proceed on an "All Plaintiffs" basis. A contrary intention or result would obviate all benefits of having consolidated the many separate actions. Each Plaintiff 's case depends upon expert testimony to prove both exposure and medical causation. Expert discovery is complete, and all expert reports have been filed. Thus, to the extent that the expert testimony of record fails to meet the test _________________________________________________________________ 14. As things developed, one of the defendants' test case selections withdrew from the test group. Consequently, the District Court permitted defendants to chose one of the parties originally selected by plaintiffs to be dismissed from the test case group. In re TMI Litigation Consolidated Proceedings, 927 F. Supp. 834, 837 n.5 (M.D. Pa. 1996). Thus, the test case group consisted of ten plaintiffs. 15. Those plaintiffs are: Paula Obercash, acute lymphocytic leukemia; Gary Villella, chronic myelogenous leukemia; Leo Beam, chronic myelogenous leukemia; Joseph Gaughan, thyroid cancer; Lori Dolan, Hurthle cell carcinoma; Jolene Peterson, thyroid adenoma; Richard Ward, osteogenic carcinoma of the right leg; Pearl Hickernell, breast cancer; Ethelda Hilt, adenocarcinoma of the ovaries; and Kenneth Putt, bladder cancer, acoustic neuroma. 16  Plaintiffs' evidentiary burden at this state of the litigation, it will fail to meet the same burden as to every Plaintiff. It would be an exercise in futility and a waste of valuable resources to allow the many separate actions consolidated under this caption to proceed if it were clear that the cases could not withstand a motion for summary judgment. Under such circumstances, the court's summary judgment ruling will be applicable to all Plaintiffs. 927 F. Supp. at 838. The District Court ruled on the merits of the summary judgment motion that the Trial Plaintiffs had failed to present either direct or indirect evidence of the doses of cancer inducing levels of radiation that they were exposed to. Id. at 870. Accordingly, the court extended its grant of summary judgment to all of the plaintiffs' cases. Because the court finds the quantum of evidence on the issue of dose to be insufficient, and because no Plaintiff will be able to state a prima facie case without adequate dose evidence, the instant ruling is binding on all Plaintiffs. Id. at 838. Accordingly, the court granted summary judgment against all of the plaintiffs, both trial and nontrial. These appeals followed. Appeal Number 96-7623 is the appeal of the ten Trial Plaintiffs. They argue that the District Court improperly excluded their proffered expert witnesses' testimony on dose exposure, thereby erroneously subjecting them to summary judgment. They do not argue that summary judgment was improper given the District Court's Daubert rulings. Thus, if we determine that the District Court's exclusion of their dose exposure testimony was proper, we must affirm the summary judgment for the defendants against the trial plaintiffs. Consequently, the primary issue for our determination in case number 96-7623 is the propriety of the District Court's exclusion of testimony of the dose exposure experts. If, however, we decide that the court improperly excluded some or all of that evidence, we 17  must then decide whether the evidence that was admissible is sufficient to create a genuine issue of material fact. Appeal Number 96-7624 is the appeal of all of the TMI personal injury plaintiffs except the ten Trial Plaintiffs. Appellants there argue that the District Court improperly extended its Trial Plaintiffs' summary judgment decision to them. Appeal Number 96-7625 is the appeal of sanctioned counsel for the majority of the plaintiffs. Counsel argue that the District Court's imposition of monetary sanctions against them for discovery violations was improper. Each appeal is considered separately. It is both impractical and unwise to begin our analysis of the Daubert challenge to the scientific testimony without first providing a brief discussion of the fundamental principles of nuclear physics, nuclear engineering, the TMI- 2 accident, ionizing radiation, and the health effects of ionizing radiation on the human body. These scientific principles are at the center of the damage that plaintiffs claim they suffered as a result of the TMI accident and the District Court's Daubert rulings. Total immersion in the complexities of these disciplines is neither required, nor possible. Accordingly, we offer the following overview of the controlling principles with an awareness that doing so stretches the boundaries of our institutional competence, and with a recognition of our need to borrow heavily from others in academic disciplines far from the familiar confines of the law. III. SCIENTIFIC BACKGROUND A. Overview of Relevant Principles of Nuclear Physics. 1. Atomic and Nuclear Structure. Plaintiffs alleged that the accident at TMI resulted in a release of radiation into the atmosphere that caused changes to the atomic structure of their chromosomes and resulted in the formation of neoplasms. Their allegations thus implicate the structure of the atom -- the basic 18  building block of matter -- and the physics of orbiting electrons.16 The atom consists of a small but massive central nucleus surrounded by one or more orbital electrons. JOHN R. LAMARSH, INTRODUCTION TO NUCLEAR ENGINEERING 8 (2d ed. 1983). Orbiting electrons are negatively charged, much smaller in mass than the neutron, and their distances from the nucleus are much larger than the radius of the nucleus. DAVID BODANSKY, NUCLEAR ENERGY: PRINCIPLES, PRACTICES AND PROSPECTS 346 (1996). The average distance from the nucleus to the place where the outermost electron is found provides an approximate measure of atomic size. This distance is approximately the same for all atoms, except a few of the lightest atoms, and is about 2 #46# 10 -8 centimeters.17 LAMARSH, at 11. The nucleus has two constituent parts of approximately equal mass -- the neutron and the proton.18 BODANSKY, at 346. Each is much more massive than the electron. LAMARSH, at 6-7. Together, they are called nucleons. BODANSKY, at 346. The neutron and proton differ in that the neutron is neutral while the proton has a positive charge equal in magnitude to the negative charge of the electron. Id. An atom is neutral or "un-ionized" when the number of positively charged protons equals the number of negatively charged electrons. D. J. BENNET, ELEMENTS OF NUCLEAR POWER 1 (2d ed. 1981).19 "Nuclides" are very important to our _________________________________________________________________ 16. As we discuss below, radiation has the potential to fatally interfere with one of more orbiting electrons. 17. It is difficult to define the exact size of an atom because the orbiting electrons may at times move very far from the nucleus but at other times pass close to it. LAMARSH, at 7. 18. At one time, it was believed that neutrons and protons were the fundamental particles of nature. However, it is now understood that they are not the fundamental particles of nature, but themselves are composed of more elementary particles called quarks. BODANSKY, at 346. While knowledge of the existence of quarks and other elementary particles is crucial to an understanding of the origins of the universe and of the ultimate structure of matter, their existence can be ignored in a discussion of nuclear reactors, radioactivity and nuclear fission. Id. 19. Forces exist in an atom that are critical to atomic structure. "Coulomb repulsion" is an electrostatic force, governed by Coulomb's 19  discussion. They are differing "species" of atoms whose nuclei contain particular numbers of protons and neutrons. LAMARSH, at 8. A nuclide is given the shorthand notation AZ X, where X is the symbol for the chemical element, Z is the atomic number and A is the atomic mass number. KNIEF, at 29. In general practice, however, the subscript Z is omitted _________________________________________________________________ law, which exists between objects that carry the same electrical charge. BODANSKY, at 349 n.3. The repulsion exists not only on a macroscopic scale, but also on an atomic scale, BENNET, at 8, and, therefore, it exists between the protons in the nucleus because they are positively charged. Consequently, Coulomb repulsion tends to disrupt (or burst) the nucleus. Id. The fact that the nucleus of a stable atom is not disrupted indicates that there is another force which overrides Coulomb repulsion, and holds the nucleus together. Id. This force, known as the "strong" or "nuclear force", exists between particles that are incredibly close to each other, within about 3 #46# 10-15 meters. The strong force acts with approximately equal strength between two protons, two neutrons or a proton and a neutron and binds the nucleus together, so long as the separation between the particles is less than 3#46# 10-15 meter space in which the strong force operates to cancel Coulomb repulsive. Id. Coulomb repulsion is not the only electrostatic force defining atomic structure. "Coulomb attraction" exists between oppositely charged particles and this attractive force, operating between the electrically positive protons and the electrically negative electrons, causes the electron to orbit around the nucleus of the atom. RONALD ALLEN KNIEF, NUCLEAR ENGINEERING: THEORY AND TECHNOLOGY OF COMMERCIAL NUCLEAR POWER 29 (2d ed. 1992). The chemical properties of an element are determined by the number of electrons surrounding the nucleus in an un-ionized atom, and the number of electrons orbiting the atom is equal to the number of protons in the nucleus. BODANSKY, at 346. That is, a neutral atom has the same number of protons and electrons, and the number of protons in the nucleus, (given the symbol "Z"), is the atomic number of a particular element and identifies it. KNIEF, at 29. Electrons are responsible for the chemical behavior of the atoms and they identify the chemical elements. LAMARSH. at 8. Consequently, each element is identified in terms of its atomic number, Z. BODANSKY, at 346. The number of neutrons in the nucleus is known as the "neutron number" and is denoted by the letter "N". L AMARSH, at 8. The sum of the number of neutrons and protons, i.e., nucleons, in the nucleus is called the atomic mass number or "mass number", A. Thus, the formula: A = Z + N. Id. 20  because once the element, X, is given, so is the atomic number, Z. BODANSKY, at 346. Nuclides whose nuclei contain the same number of protons, i.e., the same Z, but different numbers of neutrons, i.e., different N and therefore a different mass number, A, are called isotopes of the element. BENNET, at 2. All elements have a number of isotopes, Id., and they are virtually identical in their chemical properties to the elements they are isotopes of. BODANSKY, at 346. However, the masses and other characteristics of their nuclei are different. BENNET, at 2. An isotope of an element is given the same shorthand notation as the nuclide. For example, naturally occurring oxygen, whose chemical symbol is "O", consists of three isotopes, 16 O, 17O, and 18O. Id. Each has 8 protons and electrons, i.e., the same atomic number, Z, but they have 8, 9 and 10 neutrons respectively, i.e., different N (N = A - Z). The nuclei of a given element can have the same mass number, A, but have a different atomic number, Z, in which case it is called an isobar. BODANSKY, at 346. Though counterintuitive in the extreme, it is nevertheless a fact of atomic structure that the mass of an atom is less than the sum of the masses of its constituent parts. BENNET, at 4; BODANSKY, at 350; KNIEF, at 29; LAMARSH, at 28. The difference between the mass of the assembled atom and the sum of the mass of the component atomic parts is known as the "mass defect". KNIEF, at 29. However, mass is not really lost in the assembly of an atom from its component parts. Rather, the mass defect is converted into energy when the nucleus is formed. Id. The conversion is explained by the "principle of the equivalence of mass and energy in which Einstein stated that mass and energy are different forms of the same fundamental quantity."20 BENNET, at 4. Therefore, in any reaction where there is a reduction in mass, the decrease is accompanied by a release of energy. Id. The energy associated with the mass defect is called "binding energy" and it represents the total energy that would be required to disassemble a nucleus into its constituent neutrons and protons. BODANSKY, at 350. _________________________________________________________________ 20. The equivalence between mass and energy is expressed in Einstein's famous equation, E = mc2, where E is energy, m is mass and c is the speed of light. KNIEF, at 28. 21  Binding energy increases in a nucleus as the number of particles in the nucleus increase. In other words, binding energy increases with a corresponding increase in atomic mass number. LAMARSH, at 28. However, the rate of increase is not uniform. KNIEF, at 30. The amount of binding energy in a nucleon is important when determining possible sources of nuclear energy. LAMARSH, at 28. A nuclei is stable or tightly bound when the binding energy per nucleon is high. Accordingly, a relatively large amount of energy must be supplied to break the stable nuclei apart. Id. When a tightly bound nucleus is broken apart and two nuclei of intermediate mass are formed, a relatively large amount of energy is released. BENNET, at 7. In contrast, nuclei with low binding energy per nucleon are easily broken apart, and less energy is released. LAMARSH, at 29. The now familiar term, "nuclear fission" refers to the process of causing a tightly bound nucleus to split into two nuclei of intermediate mass. Id. The process proceeds in the direction of increased binding energy per nucleon. B ENNET, at 7. That is, the nuclei of intermediate mass created by the fission process have greater binding energy than the original nucleus. LAMARSH, at 30. When the nuclei of intermediate mass have greater binding energy than the original nucleus, energy is released during the formation of the final nuclei. BODANSKY, at 351. This energy that is released as a result of the fission process is the source of energy in a nuclear reactor. LAMARSH, at 30. It is what we commonly refer to as "nuclear energy". Atoms can exist only in certain states or configurations, with each state having its own specific energy. B ODANSKY, at 351. The different energy states correspond to different electron orbits of different radii, LAMARSH, at 15, each with an energy level equal to the sum of the kinetic and potential energies of the electron in its orbit. B ODANSKY, at 351. The lowest state of energy is called the "ground state" and it is the state in which the atom is normally found. LAMARSH, at 15. However, an electron can, as a result of a nuclear reaction, jump from its normal orbit to an orbit that is farther from the nucleus. An increase in energy corresponds to this "jump", and when an atom has more 22  energy than its ground state it is said to be in an"excited state". BENNET, at 8. An atom can have a number of excited states which correspond to the number of jumps the electron has made. Id. The highest energy state occurs when the electron is completely removed from the atom. LAMARSH, at 15. The complete removal of an electron from an atom is called "ionization" and the resulting atom is said to be "ionized". Id. The nucleons in the nuclei also move in orbits; however, the orbits of nucleons are not as well defined, and are not as well understood, as the orbits of electrons. L AMARSH, at 16. Like atoms, nuclei normally exist in the ground state. BENNET, at 8; BODANSKY, at 352. However, nuclei can reach excited states just as atoms can. BENNET, at 8; BODANSKY, at 352. The process is more complicated in nuclei than in atoms because excitation of nuclei can result in several nucleons being raised to excited levels simultaneously. BENNET, at 8. Although it is not yet possible to account theoretically for the exact energy levels of nuclei, as it is possible to do so for atoms. BODANSKY, at 352. It is generally true that the energies of the excited states and the energies between states are much greater for nuclei than for atoms. LAMARSH, at 16. The greater energy results from the greater forces acting between nucleons. These forces are much stronger that the forces acting between electrons and the nucleus. Id. With a few exceptions, excited states in either atoms or nuclei exist for only a very short time, about 10 -14 seconds. BENNET, at 9. Excess energy is quickly emitted and the system, either atomic or nuclear, decays to states of lower energy until it ultimately returns to its ground state. LAMARSH, at 15. The process of going from one state to another is called a "transition". Id. The energy lost in a transition is usually carried off by electromagnetic radiation,21 BENNET, at 9; BODANSKY, at 352, with the lost _________________________________________________________________ 21. Sometimes, however, the energy can be transferred to an electron through a process known as "internal conversion" which leaves the nuclide unchanged. At other times, an excited state can decay be emitting a particle, such as a beta (b) particle or a neutron, thus changing the atomic number of the nuclide. BODANSKY, at 352 n.8. 23  energy equal to the difference in the energies of the two states.22 LAMARSH, at 15. 2. Radioactivity. As suggested by our discussion thus far, nuclei are either stable or unstable. For all practical purposes, stable nuclei remain unchanged forever. Unstable nuclei decay spontaneously into lighter nuclei pursuant to a time scale that is unique for every element (the "half-life").23 The half- life for a given element is defined as the time required for one-half of a given sample of the element to "decay." If the half-life is greater than some undefined fraction of a second, the process of decay is called "radioactivity." Half- lives vary from less than a second to many billions of years. BODANSKY, at 353. Radioactivity is then, the process by which unstable nuclei seek stability. KNIEF, at 31. Frequently, the original unstable nucleus, called the "parent nucleus", decays to another radioactive nucleus, called the "daughter nucleus." LAMARSH, at 19. There may be more than one radioactive daughter nuclei produced until stability is reached. BENNET, at 11. This process of the creation and subsequent decay of several daughter nuclei is referred to as a "decay chain". LAMARSH , at 19.24 _________________________________________________________________ 22. The electromagnetic radiation corresponding to an atomic or nuclear transition is contained in a single discrete packet called a "photon". BODANSKY, at 352. At one time, light and other forms of electromagnetic radiation were described as waves. However, it is now known that electromagnetic radiation behaves at times like a particle. Id. Thus, a photon is both wave-like and particle-like in character. LAMARSH, at 7. Visible light is associated with transitions involving the outer electrons of atoms. X rays correspond to transitions involving the inner electrons of atoms. Gamma (g) rays correspond to transitions from nuclei. However, all are photons and there is no difference among them other than their energy, with visible light having the lowest energy and gamma (g) rays having the highest energy. In fact, there is really no need to distinguish between photons from atomic transitions, i.e., x rays, and photons from nuclear transitions, i.e., g rays. The names date from the time of their discovery and are probably kept only as a reminder of their origin. BODANSKY, at 352. 23. Sometimes designated as: "T1/2 ". 24. For example, there are three natural radioactive decay chains whose parent isotopes have very long-half lives. The three are uranium 238 (T1/2 = 4.51 x 109 years), uranium 235 (T1/2 = 7.1 46 x 108 years), and thorium 232 (T1/2 = 1.41 x 1010 years), and their decay chains contain many radioactive daughter isotopes leading eventually in each case to a stable isotope of lead. BENNET, at 18-19. 24  The exact time at which any single nucleus will decay cannot be determined. KNIEF, at 34. However, the average behavior of a very large sample of radioactive material can be described statistically. BENNET, at 15. For a given nuclide, there is an average time, called the "decay constant", which characterizes its rate of decay. Id. The decay constant is defined as the probability per unit of time that a decay will occur. KNIEF, at 34. The amount of radioactivity present during a decay is referred to as "activity". F RED A. METTLER, JR., M.D., AND ARTHUR C. UPTON, M.D., MEDICAL EFFECTS OF IONIZING RADIATION 7 (2d ed. 1995) (hereinafter "MEDICAL EFFECTS"). The activity of a given sample is the average number of disintegrations per unit of time. For a large sample, the activity is the product of the decay constant and the number of atoms present. Id. The traditional unit for measuring radioactivity is the curie (Ci), which is defined as 3.7 #46# 1010 disintegrations per second.25 A radioactive nuclide is called a "radionuclide." KNIEF, at 32. During the process of radioactive decay, the nucleus spontaneously emits an alpha (a) particle or a beta (b) particle. BODANSKY, at 354. The emission of these particles is often accompanied by the emission of one or more gamma (g) rays. Id. An alpha (a) particle is a highly stable nucleus of the isotope helium 4 (4He), consisting of two protons and two neutrons. LAMARSH, at 20.26 Alpha (a) particles have a double positive charge and are emitted in a discrete energy spectrum. Id. They have a low level of energy and, therefore, are only capable of penetrating matter a small distance.27 Decay by alpha particle emission is rather rare for nuclides lighter than lead (Pb) which has an atomic number (Z) of 82. BODANSKY, at 355. However, many of the naturally _________________________________________________________________ 25. The curie, is however, being superseded by a new measuring unit called the "Becquerel" (Bq), which is defined as one disintegration per second. BENNET, at 16. 26. Thus, the emission of an alpha (a) particle reduces the atomic number (Z) of the unstable nuclei by two and the mass number (A) by four. LAMARSH, at 20. 27. The most energetic of the alpha (a) particles are stopped after passing through less than 10 centimeters of air or about 0.1 millimeters of a material such as water. BODANSKY, at 355. 25  occurring radioactive elements with atomic numbers between 84 (polonium) and 92 (uranium), i.e., the heavier elements, decay by alpha particle emission. BENNET, at 13. When these elements decay, the daughter product is closer to the stability region than the parent. Id. In addition, the daughter nucleus of these heavier elements is frequently formed at an excited state of energy so that the excited nucleus immediately decays further to its ground state by the emission of gamma (g) radiation. Id. Thus, the decay of a heavy radioactive isotope by alpha particle emission also produces gamma (g) radiation. Id. A beta (b) particle is an electron of nuclear, not orbital, origin, KNIEF, at 33, but it is identical to the electrons that orbit the nucleus. BODANSKY, at 355. Because it is an electron, it has much less mass than an alpha particle. Id. A neutron that is bound into the nucleus is not stable. LAMARSH, at 7. During decay, a neutron in the nucleus is transformed into a proton and an electron and it is this electron which is emitted as a beta (b) particle. Id.; BENNET, at 13. Because beta (b) particle decay has the effect of transforming one of the neutrons into a proton, the resulting daughter nucleus has the same mass number (A) as the parent, but its atomic number (Z) is greater by one. Id. Moreover, the daughter nucleus may be formed in an excited state, and decay to its ground state by the emission of gamma (g) radiation. Id. In most cases, beta particles are negatively charged and are more properly designated as b- particles. Positive electrons, called "positrons" or b+ particles, are emitted from artificial radionuclides that are produced when positive particles, such as protons or alpha (a) particles, combine with a nucleus to form an unstable proton-rich nucleus. BODANSKY, at 355. These beta particles are very rare in naturally existing material. Id. Beta (b) particles do not all have the same energy. BENNET, at 13. The spectrum of the energy of these particles, ranges from zero to a fixed maximum or "endpoint energy." BODANSKY, at 357.28 However, the average energy of beta _________________________________________________________________ 28. The endpoint energy corresponds to the mass difference between the parent atom and the residual product, as the principle of conservation of mass plus energy demands. BODANSKY, at 357. 26  particles is about one-third, BENNET, at 13, to one-half, BODANSKY, at 357, the endpoint energy. The remaining two- thirds to one-half of maximum possible beta (b ) particle energy is shared with another particle called the neutrino.29 BENNET, at 13; BODANSKY, at 357. A neutrino is one of nature's more curious phenomena. It has no charge, and virtually no mass. KNIEF, at 33. It was once thought to have no mass; however, it is now believed that the neutrino may have mass, albeit very small mass. BODANSKY, at 357; Malcolm W. Browne, Los Alamos Experiment Shows Neutrino Probably Has Mass, N.Y. Times, May 7, 1996. Beta (b) particle decay usually occurs when a nuclide has an excess of neutrons. BENNET, at 13; B ODANSKY, at 358. A beta particle has greater penetrating ability than an alpha particle, BENNET, at 21, with average penetration distances ranging from 0.1 to 1 g/cm2, increasing with increasing energy. BODANSKY, at 355. A neutrino, however, has great penetrating power and can pass through very large amounts of material without stopping. Id. at 358. As discussed earlier, gamma (g) radiation is electromagnetic radiation emitted in the form of photons by nuclei in excited states of energy. Except as noted below, gamma (g) emission is not a primary process of radioactive decay. Instead, it follows alpha (a) particle or beta (b) particle emission. Gamma (g) rays do not have mass or charge, and they are therefore capable of much greater penetration of matter than alpha (a) or beta (b) particles.30 BODANSKY, at 355. Earlier, we noted that excited states in nuclei exist for a very short time (about 10-14 seconds). Consequently, half- lives for gamma (g) ray emission are typically very short. BODANSKY, at 359. However, some nuclei have long-lived _________________________________________________________________ 29. Strictly speaking, the neutrino emitted in b#48# decay is an anti- neutrino, while the neutrino itself is emitted in b+ decay. When the distinction between them is not important, they are both referred to as neutrinos. Again, strictly speaking, the b#48# and neutrino are called particles, while the b+ and anti-neutrino are called anti-particles. BODANSKY, at 357. 30. Gamma rays can penetrate to distances ranging from 5 to 20 g/cm2. BODANSKY, at 355. 27  excited states, called "isomeric states", with half-lives ranging from a fraction of a second to many years. Id. In fact, in some cases, the excited state is so long that the nuclei appear semi-stable. LAMARSH, at 21. The decay to a lower state of energy by gamma (g) ray emission in a nuclei in an isomeric state is called an "isomeric transition". Id. In such a case, gamma (g) ray emission appears to be the primary radioactive process of, rather than incident to, alpha (a) or beta (b) particle emission. Gamma ray emission can, however, ultimately be traced back to either initiating process.31 BODANSKY, at 359. 3. Ionizing Radiation. The legal dispute before us is rooted in the damage that purportedly resulted from defendants' release of ionizing radiation into the atmosphere. There are a number of ways in which an ion, or charged particle, can interact with an atom. First, because it is charged, the particle exerts an electrostatic or "Coulomb force" on the atom's electrons. The exertion of Coulomb force has various effects upon an atom. One or more of the electrons may move to an outer orbit, leaving the atom in an excited state of energy or an electron may be entirely ejected from the atom. The latter event results in the formation of an ionized atom. L AMARSH, at 88. When an atom is ionized, it is split into an ion pair. The negatively charged electron of this pair is the negative ion, and the atom minus its negatively charged electron is the positive ion. BENNET, at 20. This process of ionization produces ionizing radiation.32 MEDICAL EFFECTS, at 1. The second possible result is that the charged particle may penetrate the cloud of orbiting electrons and collide with the nucleus. After collision, the charged particle is scattered from the nucleus, and, since momentum and _________________________________________________________________ 31. There is an alternative to gamma (g) ray emission called "internal conversion", in which the excitation energy is transferred to one of the inner electrons of the atom. Typically, gamma (g ) ray radiation and internal conversion are competing processes by which excited nuclei reach the ground state. BODANSKY, at 359. 32. Ionizing radiation is only a small part of the electromagnetic spectrum, which includes radio waves, radar, microwaves, ultraviolet radiation and electric power. MEDICAL EFFECTS, at 1-2. 28  energy are conserved in the collision, the nucleus recoils. If the charged particle has sufficient mass and energy, the recoiling nucleus may be ejected from its own electron cloud and itself become a charged particle. LAMARSH, at 88. In addition, under certain circumstances, the charged particle, particularly if it is an alpha (a) particle, may undergo a nuclear reaction when it collides with the nucleus. The charged particle may also be accelerated by the electrostatic or Coulomb field of the electrons or the nucleus and a photon may be emitted.33 Id. Whichever of these alternative results occurs, a charged particle is created. When a charged particle passes through matter, it excites and ionizes atoms in its path. Id. However, these charged particles lose energy by virtue of the electrostatic forces created by their interaction with the atoms that comprise the matter through which the charged particles pass. KNIEF, at 70. The electrostatic forces acting upon the charged particles are proportional to the product of the charges and inversely proportional to the square of the distance between them. Thus, the force decreases rapidly with distance, but becomes negligible only at very large distances. Id. At any given interval, a charged particle experiences forces from a very large number of electrons. The resulting energy losses are well defined for each charged particle and each material medium. Id. The net macroscopic effect of charged-particle interactions is characterized by range and linear energy transfer ("LET"). Id. Range is the average distance traveled by a charged particle before it completely stops. The LET is the amount of energy deposited per unit of particle track, which gives rise to the excitation and ionization. LAMARSH , at 89. The range and the LET of a specific radiation contribute to the effect they have on a material, with the range determining the distance of penetration and the LET determining the distribution of energy deposited along the path. K NIEF, at 70. The LET is of particular significance to an inquiry into the biological effects of radiation. Those effects depend _________________________________________________________________ 33. This latter kind of radiation that is emitted when a charged particle becomes accelerated, is called "bremsstrahlung". Id. LAMARSH, at 88. 29  upon the extent to which energy is deposited by radiation as excitation and ionization within a given biological system. LAMARSH, at 89. The LET increases with the mass and charge of a moving particle. Id. Consequently, heavy charged particles, such as alpha (a) particles, are referred to as high LET radiation. Id. Charged particles, are referred to as "directly ionizing radiation" because they are directly responsible for producing ionization. LAMARSH, at 88; B ENNET, at 20; BODANSKY, at 354. Uncharged particles, such as gamma (g) rays, lead to excitation and ionization only after interacting with matter and producing a charged particle. Accordingly, uncharged particles are referred to as "indirectly ionizing radiation." LAMARSH, at 88. While gamma (g) rays can interact with matter in a variety of ways, there are, for purposes of our analysis, three important types of interaction between gamma (g) radiation and matter -- the "photoelectric effect", "pair production" and "Compton scattering." BENNET, at 21. Because very short-range forces govern electromagnetic mechanisms, a gamma (g) ray must essentially"hit" an electron for an interaction to occur. KNIEF, at 71. In the photoelectric effect, which is the most important process at low gamma (g) ray energies, BENNET, at 199, the gamma (g) ray interacts with the entire atom, the gamma (g ) ray disappears and one of the atomic electrons is ejected from the atom. LAMARSH, at 79. As a result, the energy of the gamma (g) ray or photon is converted completely to kinetic energy of an orbital electron. KNIEF, at 71. If the gamma (g) ray ejects an inner electron, the resulting hole in the electron cloud is filled by one of the outer electrons. LAMARSH, at 16, 79. This transition is accompanied either by the emission of an X ray or by the ejection of another electron. Pair production occurs only for high-energy gamma (g) rays and only in the vicinity of a heavy nucleus. Id. at 80; BENNET, at 21. The gamma (g) ray is annihilated; and an electron pair -- a positron and a negatron -- is created. LAMARSH, at 80. When this occurs the energy of the gamma (g) ray converted to mass, and kinetic energy of the electron pair. KNIEF, at 71. Once they are formed, the positron and 30  negatron move around and ultimately lose energy as a result of collisions with atoms in the surrounding matter. LAMARSH, at 80. After the positron has slowed to very low energies, it combines with a negatron, the two disappear and two photons are produced. LAMARSH, at 80-81. The photons that are produced are called "annihilation radiation." Id. at 7. Compton scattering occurs when the gamma (g) ray strikes an electron and is scattered. The electron that is struck in this process recoils and acquires some of the kinetic energy of the gamma (g) ray, Id. at 81, thus reducing the energy level of the reaction. KNIEF, at 71. Since the gamma (g) ray does not disappear as it does during the photoelectric effect, and is not annihilated as it is in pair production, the Compton-scattered gamma (g) ray is free to interact again. LAMARSH, at 82. Although uncharged particles cause indirect ionizing radiation, it is nonetheless possible to refer to the LET of uncharged particles. However, because they have a relatively low rate of energy loss when compared to the rate of energy loss of charged particles, gamma rays (g) are referred to as "low LET radiation." LAMARSH, at 89. The distinction between high LET radiation and low LET radiation has important biological consequences. Id. Given the same dose of radiation, biological damage from high LET radiation is much greater than damage from low LET radiation. Id. at 402. 4. Radiation Quantities and Units. Radiation can be measured by counting the number of ionized particles it produces as it passes through air. INTERNATIONAL ADVISORY COMMITTEE, THE INTERNATIONAL CHERNOBYL PROJECT, TECHNICAL REPORT 20 (1991) (hereinafter "CHERNOBYL "). Originally, the amount of radiation exposure for X- and gamma (g) radiations was measured in units of the roentgen (R), KNIEF, at 72, which is defined as the number of electrical charges produced in a unit mass of air. CHERNOBYL, at 20.34 Alternatively, a roentgen can be defined _________________________________________________________________ 34. One roentgen is that quantity of X or gamma (g) radiation which produces a total charge of one electrostatic unit of either sign in one cubic centimeter of air at 1 atmosphere at 0o Celsius. LAMARSH, at 400. 31  in terms of the amount of energy released in the production of ions with a total charge of one electrostatic unit of either sign. BENNET, at 197.35 Thus, the roentgen is a unit of exposure in air and not a unit of radiation dose to body tissue. Moreover, it is not applicable to higher energy X- rays or to particulate radiations. MEDICAL EFFECTS, at 8. Consequently, the roentgen is not very useful for comparing the effects of various radiations on biological systems, particularly the human body. KNIEF, at 73. When radiation penetrates material, its energy is absorbed and released by the constituent atoms of the material that is penetrated. CHERNOBYL, at 20. The absorbed energy per unit mass of material is termed the "absorbed dose." Id.36 Two units are used to measure absorbed dose of any type of radiation. The original unit of absorbed dose is the "rad" (radiation absorbed dose) and is defined as 100 ergs of energy per gram of material. LAMARSH, at 401. The new unit of absorbed dose under the Systeme International d'Unites ("SI")37 is the gray ("Gy"), which is defined as one joule of energy absorbed per kilogram of matter. CHERNOBYL, at 20. Because a rad and a gray are defined in terms of energy, it is possible to equate rads with grays, with one gray being equivalent to 100 rads (1Gy = 100 rads), or one _________________________________________________________________ 35. Under this definition, a roentgen is equivalent to depositing about 88 "ergs" in 1 gram of air. KNIEF, at 73. An "erg" is a unit of energy and one roentgen under the alternative energy description is energy sufficient to move the point of a sharpened pencil about 1.5 millimeters across a piece of paper. Id. 36. Heavy, highly charged particles, such as alpha (a) particles, lose energy rapidly over distance and, therefore, do not penetrate matter deeply. For example, alpha (a) particles do not penetrate the layer of dead cells on the surface of the skin. CHERNOBYL, at 19. Beta (b) particles, because of their smaller charge and much smaller mass, are much more penetrating, BENNET, at 20, and may penetrate up to several centimeters into the body. CHERNOBYL, at 19. X- and gamma (g) rays have much greater penetrating power than either alpha (a ) or beta (b) particles, BENNET, at 20, and they are therefore used for medical diagnostic purposes. CHERNOBYL, at 19. 37. The SI is a modernized metric system which is becoming the standard for expressing scientific and technical data. However, much scientific and technical literature still contains the older, more customary units. KNIEF, at 671 32  rad equivalent to 10 milligrays (1 rad = 10 mGy). 38 MEDICAL EFFECTS, at 8. However, the absorbed dose is not the only factor to be considered in estimating radiation effects on the human body. The effects also depend on the LET of the radiation. KNIEF, at 73; LAMARSH, at 402. Even when the amounts of energy absorbed are the same, alpha (a) particles are more damaging to human tissue than gamma (g) radiation because of the higher LET of alpha (a) radiation. BENNET, at 198. The fact that different types of radiation have different biological effects for the same absorbed dose is described in terms of the relative biological effectiveness ("RBE") of the radiation. LAMARSH, at 402. The RBE depends on the dose, the dose rate, the physiological condition of the subject, and various other factors. The RBE is determined through experimentation. KNIEF, at 73; LAMARSH, at 403. Accordingly, there is no one RBE for a given type of radiation, and the unit is used almost exclusively in radiobiology. L AMARSH, at 403. RBE is, however, used to approximate the quality factor ("Q") of radiation, which is usually the upper limit of RBE for a specific type of radiation. Id.; K NIEF, at 73. For example, X-rays and gamma (g) rays have a Q of 1, beta (b) particles have a Q of 1 to 1.7, depending on their energy, and alpha (a) particles have a Q of 20. C HERNOBYL, at 20; KNIEF, at 74. To estimate the effect of a given type of radiation on body tissue, it is necessary to determine the dose equivalent. The dose equivalent is arrived at by multiplying the absorbed dose by the quality factor of the radiation. The original unit of dose equivalence is the "rem" (roentgen equivalent man) and is the product of the absorbed dose in rad and the Q of the particular radiation. LAMARSH, at 404. Thus, if the radiation is gamma (g) _________________________________________________________________ 38. There is another type of unit which is sometimes used for very high energy radiation and for particulate radiation. That unit is the "kerma" (kinetic energy released inmatter) and it is used because it includes not only the energy deposited in the local area but also the additional energy deposited as a result of bremsstrahlung. For most purposes, the rad and the kerma are interchangeable. A major exception is the calculation of doses for atomic bomb survivors. There, the kerma was higher than the rad. MEDICAL EFFECTS, at 8. 33  radiation, then an absorbed dose of 1 rad produces a dose equivalent of 1 rem, and if the radiation is alpha (a) particle radiation, then an absorbed dose of 1 rad produces a dose equivalent of 20 rem. The new SI unit of dose equivalence is the sievert (Sv) and is the product of the absorbed dose in gray (Gy) and the Q of the radiation. BENNET , at 198. Since one gray equals 100 rads (1 Gy = 100 rads), then one sievert equals 100 rem (1 Sv = 100 rem), LAMARSH , at 404, or one rem equals 10 millisieverts (1 rem = 10 mSv). MEDICAL EFFECTS, at 8. The effect of a given dose equivalent varies depending on the tissue or organ exposed to the radiation. CHERNOBYL, at 20. For example, a given dose of radiation to the hand may have a different and far less serious effect than the same dose delivered to a blood-forming organ. Similarly, the biological effect of a given dose of radiation to a blood- forming organ will be different from a like exposure to reproductive tissue. LAMARSH, at 404. However, equal dose equivalents from different sources of radiation, if delivered to the same point in the body, should have approximately the same biological effect. Id. at 403. The "effective dose" (E), is a unit that is derived from the equivalent dose in an attempt to indicate the combined effect of different doses of radiation upon several different tissues or body parts. CHERNOBYL, at 20. The effective dose is the product of the equivalent dose in a tissue or organ (T) multiplied by a factor called the "tissue weighing factor" (WT), which represents the contribution of that tissue or organ to the total harm resulting from uniform radiation exposure to the whole body. Id.39 Each of the preceding units, (i.e., absorbed dose, equivalent dose and effective dose) relate to the radiation exposure of an individual. There are, however, units of exposure for groups of people. They are arrived at by _________________________________________________________________ 39. By way of illustration, the tissue weighing factor for the gonads is 0.20, the tissue weighing factor for red bone marrow is 0.12, and the tissue weighing factor for the skin and bone surface is 0.01. CHERNOBYL, at 20. The effective dose is the weighted sum of the equivalent doses in all the tissues and organs of the body and is a measure of the total risk from any combination of radiations affecting any organs of the body. Id. 34  multiplying the average dose to the exposed group by the number of people in the group. CHERNOBYL, at 20-21. The units are the "collective equivalent dose," which relates to a specified tissue or organ, and the "collective effective dose," which relates to all the people exposed to the radiation. Id. Both units are expressed in terms of man-rems or man- sieverts. LAMARSH, at 405, and they represent the total consequences of the exposure of a population or group. CHERNOBYL, at 21. 5. Health Effects of Ionizing Radiation. Soon after the discovery of x-rays and natural radioactivity, clinical evidence suggested that ionizing radiation is harmful to human tissue. ANNALS OF THE INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, ICRP PUBLICATION 60, 1990 RECOMMENDATIONS OF THE INTERNATIONAL COMMISSION ON RADIOLOGICAL P ROTECTION 94 (1990)(hereinafter "ICRP 60"). The initial evidence was mainly noted from the effect of ionizing radiation on human skin.40 Id. at 92. Later, scientists realized that exposing germinal tissue in plants and animals to ionizing radiation produced effects not only in the plants and animals that were actually exposed, but also in subsequent generations of the exposed plants and animals. Id. Scientific studies and investigations over the last century, have now given us a wealth of information about the effects of radiation on humans.41 These studies include extensive in vitro and in vivo animal experiments, Id., the comprehensive epidemiological studies of the survivors of the atomic bombings of Hiroshima and Nagasaki, studies of x-rayed tuberculosis patients; and studies of people exposed to ionizing radiation during treatment for ankylosing spondylitis, cervical cancer and tinea capitis. NATIONAL RESEARCH COUNCIL, COMMITTEE ON THE BIOLOGICAL EFFECTS OF IONIZING RADIATIONS, HEALTH EFFECTS OF EXPOSURE TO LOW LEVELSOF IONIZING RADIATION 2(1990) _________________________________________________________________ 40. Ionizing radiation causes nonmalignant skin damage called erythema or reddening of the skin. LAMARSH, at 409. 41. One commentator has noted that "more than 80,000 studies have been reported in the scientific literature, indicating that radiation effects have been studied far more thoroughly than other environmental impacts." KNIEF, at 77. 35  (hereinafter "BEIR V"). These studies have allowed science to "narrow the range of uncertainties in human radiobiology." CHERNOBYL, at 37. As noted earlier, an atom is ionized when an electron is ejected from its orbit and expelled from the atom. As ionizing radiation passes through human tissue, it can transfer its energy along the tracks of the charged particles to the atoms and molecules of the tissue and ionize the atoms and molecules of that tissue. CHERNOBYL , at 37. There are two mechanisms by which ionizing radiation can alter human cells. LAMARSH, at 409. First, the ionization can directly alter biological structures by the disruption or breakage of molecules. Id.; ICRP 60, at 96. Second, biological structures can be altered indirectly by chemical changes set in motion by the transfers of energy to the medium as the ions pass through the molecular structure of human tissue. ICRP 60, at 96. Most of this energy transfer takes place in the water of our cells simply because water is the major component of the human body. 42 MEDICAL EFFECTS, at 13; BEIR V, at 12. When an ionizing particle passes through a water molecule, it may ionize it and produce an ionized water molecule, H2O+, and an electron. The electron can be trapped and produce a hydrated electron, eaq. BEIR V, at 12. However, the ionized water molecule, H2O+, reacts with another water molecule to produce a free radical called the "hydroxyl radical, OH." Id.43 This particular free-radical is very reactive because it has an unpaired electron and seeks to pair its electron in order to stabilize itself. BEIR V, at 13. At high initial concentrations, back reactions occur which produce hydrogen molecules, hydrogen peroxide and water. Id. However, the water molecule is not always ionized in this process. It can also simply become excited and break up into the hydrogen radical, H., and the hydroxyl radical, OH.. Id. The result of this chemical process is the formation of the _________________________________________________________________ 42. Human cells are made up of 70% water. MEDICAL EFFECTS, at 13. 43. A free radical is an atom or molecule that has a single unpaired electron. MEDICAL EFFECTS, at 13. 36  three highly reactive species: the hydrated or aqueous electron, eaq, the hydroxyl radical, OH., and the hydrogen radical, H.. Id. All three are highly reactive and can damage the molecular structure of human cells. Id. Free radicals are produced almost immediately after an energy transfer.44 They move rapidly in the medium, can travel some distance from the site of the original event that creates them, and they can cause chemical changes in the medium. Id. However, even though free radicals are highly reactive and potentially very dangerous to the structure of cells in human tissue most recombine to form oxygen and water in about 10-5 seconds without causing any injury. MEDICAL EFFECTS, at 13. Ionization radiation can damage cells whether the radiation results directly from the electrons set in motion or indirectly by the chemical production of free radicals. CHERNOBYL, at 37. A great deal of evidence suggests that DNA is the principal target in an irradiated cell, and is the most critical site for lethal damage. ICRP 60, at 96; BEIR V, at 13. DNA is believed to be the "critical cellular component injured," as low doses of radiation. MEDICAL EFFECTS, at 16. The random character of energy absorption events caused by ionizing radiation can damage vital parts of DNA in several ways including single-strand or double-strand breaks in the DNA molecule. ICRP, at 96. However, it has been postulated that the majority of DNA strand breaks are not due to the direct effects of ionizing radiation, but rather are caused by the hydroxyl radical. MEDICAL EFFECTS, at 14; see also BEIR V, at 14. Irradiation can also cause a number of recombinational changes to cells. ICRP 60, at 96. Not all irradiation-caused damage to DNA is harmful. Cells have evolved complex repair systems and when a single-strand break occurs, it is quite possible that the site of the damage can be identified and the break very quickly repaired. Id.; CHERNOBYL, at 38. In such a case, the DNA structure is returned to its original form, and there is no long term cellular consequence. ICRP 60, at 96. For example, if ionizing radiation affects a single protein within _________________________________________________________________ 44. A They are created in about 10-12 seconds. BEIR V, at 13. 37  a cell, the cell can simply produce a new protein and there is no functional change. CHERNOBYL at 37. Alternatively, the repair may not return to DNA to its original form, but DNA integrity may be retained. Id. While it is possible for double strand breaks in DNA to be repaired, the consequences of a double strand break are very serious. ICRP 60, at 96. Chromosomal aberrations are a result of DNA that is damaged by irradiation. These aberrations can be measured quantitatively as a function of absorbed dose. Id. at 97. The outcome could be cell reproductive death, misrepair reflected in a mutation or extensive gene deletion. Id. at 96. If cellular damage is not repaired, it may prevent the cell from surviving or reproducing, or it may result in a viable but modified cell. CHERNOBYL, at 38. The two outcomes have severe, and different, implications for the human body, leading to either "deterministic" or "stochastic" effects. Id. Deterministic effects are entirely predictable and their severity is an inevitable consequence of a given dose. LAMARSH, at 409. Stochastic effects are those that occur at random, i.e., they are of an aleatory or statistical nature. CHERNOBYL, at 38. Thus, stochastic effects are those whose probability of occurrence, as opposed to severity, is determined by dose. LAMARSH, at 409. i. Deterministic Effects. Deterministic effects result when an organism can no longer compensate for the extent of dead cells by proliferating viable cells. ICRP 60, at 99. Cell death or cell killing is the main process involved in deterministic effects. Id. Unless the dose is very high, most types of cells are not immediately killed, but continue to function until they attempt to divide. Id. The attempt to divide will fail, probably because of severe chromosome damage, and the cell will die.45 Id. Cell death usually becomes apparent within a few hours or days after irradiation. Id. at 97. _________________________________________________________________ 45. Although individual cell death in a tissue is stochastic, the total effect of the death of a high number of cells in a tissue is deterministic. ICRP 60, at 99; CHERNOBYL, at 38. 38  Cell death is not always life threatening because most body organs and tissues are unaffected by the loss of even a substantial number of cells. CHERNOBYL, at 38. It is only when a tissue or organ absorbs a certain threshold dose high enough to kill or impair the reproduction of a significant fraction of vital cells within the tissue or organ that there is a clinically detectable impairment of function. ICRP 60, at 99. If enough cells are killed, the function of the tissue or organ is impaired. Id. at 97. In extreme cases the organism dies. Id. The severity of the effect is dependent on the dose. Id. Thus, the likelihood of a deterministic effect is zero at a dose lower than some threshold, but the likelihood increases to certainty above such a threshold dose, with the severity of the harm increasing with dose. CHERNOBYL, at 38-39. Cells that divide rapidly are very sensitive to radiation and it is in these cells that the damage from radiation appears to be the greatest. KNIEF, at 75. Such cells include lymphocytes, immature bone marrow cells and intestinal epithelium. Slightly less sensitive cells include those of the lens of the eye and the linings of the stomach, esophagus, mouth and skin. Cells of intermediate sensitivity include those of the liver, kidneys, lungs, thyroid andfibrous tissue. Cells that divide slowly or not at all are the least sensitive to radiation. CHERNOBYL, at 39. These include mature red blood cells, muscle connective tissue as well as bone, cartilage and nervous tissue. Id. Thus, if a person receives a whole body absorbed dose of 1 Gy or 100 rad, generally only those cells with very high sensitivity would be killed. However, as the whole body absorbed dose is increased, additional cells and organs could die and thereby alter the person's clinical presentation. Id. Obviously, if exposure to ionizing radiation results in damage to vital organs or tissues, it may well be fatal. Id. The likelihood of a deterministic effect is practically zero for absorbed doses below 1 Gy or 100 rad. Above that absorbed dose level, deterministic effects occur. Some examples of deterministic effects are erythema, bone 39  marrow depression, radiation cataracts, sterility, and acute radiation syndrome. Id.; MEDICAL EFFECTS, at 280.46 Clinically significant bone marrow depression has a threshold for acute absorbed doses of about 0.5 Gy or 50 rad and for protracted exposure over many years of about 0.4 Gy or 40 rad per year. CHERNOBYL, at 39. Absent appropriate medical care, bone marrow depression will result in half of the people in a heterogeneous population who are acutely exposed to a dose of about 3 to 5 Gy or 300 to 500 rad.47 Id. The threshold for opacities significant enough to cause vision impairment (which occurs after some delay) appears to be in the range of 2 to 10 Gy or 200 to 1000 rad for an acute exposure to x-rays or gamma (g) rays. The threshold for chronic exposure over many years is thought to be about 0.15 Gy or 15 rad per year. Id. Death is almost certainly the deterministic effect for an individual exposed to a whole body dose of about 6 Gy or 600 rad or higher over a short period. Id. A 3 Gy or 300 rad dose would be lethal for half of an irradiated population who receive little or no medical care, the so called"median lethal dose". Id. However, it has been postulated that for people in good health who receive very intensive medical treatment, the median lethal dose may be from 5 Gy or 500 rad to as high as 9 Gy or 900 rad. Id. _________________________________________________________________ 46. The threshold for temporary sterility in men for a single absorbed dose to the testis is about 0.15 Gy or 15 rad and the threshold under conditions of prolonged exposure is about 0.4 Gy or 40 rad. CHERNOBYL, at 39. The threshold for permanent sterility is 3.5 to 6 Gy or 350 to 600 rad for acute exposure and 2 Gy or 200 rad for prolonged exposure. Id. The threshold for permanent sterility in women is an acute absorbed dose between 2.5 to 6 Gy or 250 to 600 rad or a protracted dose over many years of about 0.22 Gy or 22 rad. Id. 47. The estimate of the number of people who would die within a certain number of days without medical attention following a significant whole body absorbed dose is called the "lethal dose estimate" and, in this example, would be expressed as "LD50/60", meaning "Lethal Dose for 50% of the population within 60 days without medical attention." KNIEF, at 76. 40  ii. Stochastic Effects. Stochastic effects are those which result when an irradiated cell is modified rather than killed. C HERNOBYL, at 39. Even at very low doses it is possible that ionizing radiation may deposit sufficient energy into a cell to modify it. ICRP 60, at 98. Thus, there is a finite possibility for the occurrence of a stochastic event even at very small doses. Id. Consequently, it is assumed that there is no threshold for the initiation of a stochastic event. Id. , at 98; MEDICAL EFFECTS, at 73. Put another way, it is believed that stochastic effects can occur even at the lowest doses and, therefore, the possibility of a stochastic effect has to be taken into account at all doses. ICRP 60, at 67. The probability that cancer will result from radiation increases proportionally with dose. ICRP 60, at 69. CHERNOBYL, at 40. However, it is currently believed that there is no threshold dose below which the probability of cancer induction is zero. ICRP 60, at 69; CHERNOBYL, at 40. It is presumed that any transformed cell can become cancerous and become a malignant tumor. CHERNOBYL, at 40. There are two generally recognized types of stochastic events. The first can occur in somatic cells and may result in the induction of cancer in the exposed person. The second can occur in cells of the germinal tissue and may result in hereditary disorders in the descendants of the irradiated.48 CHERNOBYL, at 39-40; ICRP 60, at 69, 106-07. However, even though hereditary stochastic effects have been demonstrated on highly irradiated mice, CHERNOBYL, at 42, hereditary stochastic effects have not yet been clearly demonstrated in humans. BEIR V, at 4. Thus, any such effects are based on extrapolation from mice to humans.49 _________________________________________________________________ 48. "There are approximately 4 #46# 1013 cells in the average adult person. . . . [and they] are divided into two broad classes: somatic cells and germ cells. Almost all of the cells in the body are somatic cells. These are the cells that make up the organs, tissues, and other body structures. The germ cells, which are also called "gametes", function only in reproduction." LAMARSH, at 406. 49. Such extrapolation has led to the estimate that at least 1 Gy or 100 rad of low-dose, low LET radiation is necessary to have any hereditary stochastic effect on humans. BEIR V, at 4. 41  Genetic studies of the almost 15,000 children of the survivors of the atomic bombing in Japan have not yielded evidence of a statistically significant increase in severe hereditary effects. CHERNOBYL, at 42; BEIR V, at 4. Of course, the difficulties encountered in studying the probability of hereditary effects are formidable and include the need to monitor very large numbers of people in irradiated and controlled populations. The difficulty is increased because hereditary effects caused by radiation may be indistinguishable from hereditary disease due to other causes. CHERNOBYL, at 42. It is cancer induction -- the first stochastic event -- that it as issue here. The cell modification caused by ionizing radiation is presumably the result of specific molecular DNA changes by a process known as "neoplastic transformation." It is assumed that there is no threshold for the induction of the molecular changes at the DNA site. ICRP 60, at 97, 107. The potential for unlimited cellular proliferation characteristically results from molecular changes. Id., at 107. Nevertheless, this change alone does not result in a malignant transformation because other changes occur in a malignant transformation. Id. Carcinogenesis is currently believed to be a multistep process requiring two or more intracellular events to transform a normal cell into a cancer cell. BEIR V, at 135. The changes that occur are believed to proceed sequentially. ICRP 60, at 97. The initial events in the production of a cell or cells with the potential to develop into a cancer are known as "initiation". Id. The initiated cell or cells must undergo further changes, usually after a long time and possibly after stimulation by a promoting substance or catalyst, before becoming a cell with malignant potential. Id. Thereafter, the division and multiplication of such cells gives rise to an occult tumor in the "progression" stage. Id. at 97-98. "Progression" refers to the proliferation of a subpopulation of cells within a tumor. BEIR V, at 137. This subpopulation expands and overgrows the less aggressive cells. Id. The carcinogenic process, includes the growth of a primary cancer to a detectable size (e. g., about 1 cm in diameter and containing billions of cells). In humans it can take many years for such a tumor to spread to other tissues. ICRP 60, at 98. 42  The period between exposure to radiation and possible detection of a resulting cancer is called the "latency period". Id. at 107. By way of example, the median latency period for induced leukemia may be about 8 years. The latency period for many induced solid tumors, such as tumors of the breast or lung. Id. The "minimum latency period" is the shortest time in which a specified radiation-induced tumor is believed to occur after exposure. Id. It is about two years for acute myeloid leukemia, and between 5 and 10 years for other types of cancers. Id. Significantly, the severity of a cancer does not depend on the level of the dose that triggered it. ICRP 60, at 60; CHERNOBYL, at 40. The mathematical model used to describe radiation induced cancer is the "linear risk model". BEIR V, at 4; CHERNOBYL, at 40. It is expressed as y = ax, where y is the incidence of excess cancer, a is a constant, and x is the dose. MEDICAL EFFECTS, at 81. The linear risk model posits that each time energy is deposited in a cell or tissue, there is a probability of the induction of cancer. Id. Thus, the effect of each small dose is additive, and therefore spreading a given dose out over time does not reduce the ultimate risk. Id. Although there is scientific consensus that ionizing radiation can cause cancer, ionizing radiation, is not currently known to leave a tell-tale marker in those cells which subsequently become malignant. NATIONAL COUNCIL ON RADIATION PROTECTION AND MEASUREMENTS, NCRP STATEMENT NO. 7, THE PROBABILITY THAT A PARTICULAR MALIGNANCY MAY HAVE BEEN CAUSED BY A SPECIFIED IRRADIATION 1 (1992) (hereinafter "NCRP 7"). Medical examinations and laboratory tests can determine the type and extent of a cancer, suggest an optimal treatment, and provide a likely prognosis, but they rarely (if ever) provide definite information as to its cause. Id. Consequently, medical evaluation, by itself, can neither prove nor disprove that a specific malignancy was caused by a specific radiation exposure. Id. Therefore, the primary basis to link specific cancers with specific radiation exposures is data that has been collected regarding the increased frequency of malignancies following exposure to ionizing radiation. Id. In other words, causation can only be established (if at all) from epidemiological studies of 43  populations exposed to ionizing radiation. Id.; LAMARSH, at 413. However, the task of establishing causation is greatly complicated by the reality that a given percentage of a defined population will contract cancer even absent any exposure to ionizing radiation. In industrialized countries where the life expectancy averages about 70 years, about 30% of the population will develop cancer and about 20% of the population will die of cancer. CHERNOBYL , at 42. It is estimated that if 100,000 persons with an age and sex distribution typical of the United States are exposed to a whole body dose of 0.1 Sv and are followed over their lifetimes, between 770-810 people would develop fatal cancers in excess of the normal incidence. BEIR V, at 6. 6. Radiation in the Environment. The inquiry into cause is further complicated by the fact that radiation is a "constituent element" of our environment, and mankind has been exposed to it since our first appearance on this planet. CHERNOBYL , at 23. Obviously, natural environmental radiation has been, and continues to be, augmented by man-made radiation. Consequently, "the radiation environment of today differs from that of yesterday, and it will continue to be transformed in the future." Id. The total average annual dose, from both natural radiation and man-made radiation, is 3.6 mSv or 360 mrem. BEIR V, at 18. i. Natural Radiation. There are two major sources of natural radiation. These are cosmic radiation and terrestrial radiation. L AMARSH, at 427. Cosmic radiation is highly energetic radiation that bombards the earth from outer space. Terrestrial radiation originates in radionuclides found in the earth and in our own bodies. Id. Together, cosmic and terrestrial radiation deliver the highest radiation dose that people normally receive.50 CHERNOBYL, at 23. _________________________________________________________________ 50. The average annual dose of natural radiation is 2.4 millisieverts (mSv) or 240 millirems (mrems). Natural background radiation levels vary widely throughout the world. The dose of 2.4 mSv or 240 mrems is 44  Cosmic radiation consists primarily of a highly-energetic mixture of protons (about 87%), alpha (a) particles (about 11 percent), and a trace of heavier nuclei (about 1%) and electrons (about 1%). LAMARSH, at 427. However, the atmosphere acts as a shield, greatly weakening cosmic rays before they reach earth. MEDICAL EFFECTS, at 32. About 26 cosmogenic radionuclides have been identified. They are produced by the action of cosmic radiation. LAMARSH, at 429. However, of the 26, only tritium (3H)51, beryllium-7 (7Be), sodium-22 (22Na) and carbon-14 (14C), contribute appreciably to irradiation, MEDICAL EFFECTS, at 32, and only carbon-14 (14C), is responsible for significant radiation doses. LAMARSH, at 429. Fortunately, carbon-14 is a relatively short-lived radionuclide.52 It primarily results from the atmospheric interaction of thermalized cosmic ray neutrons and nitrogen. Id. The concentration of 14C is about the same in all living species, i.e., 7.5 picocuries per gram of carbon. Id. Because approximately 18% by weight of the human body is carbon, 14C contributes an estimated annual dose of 0.007 mSv or 0.7 mrems. Id. The average dose of cosmic radiation at or near sea level is 0.37 mSv per year or 37 mrems per year. Id.; CHERNOBYL, at 23. However, the dose rate increases with altitude, doubling about every 1500 meters. CHERNOBYL, at 23. Consequently, people living at high altitudes53 may have an average annual dose level reaching 1 mSV or 100 mrems. Id. Terrestrial radiation accounts for as much as 85% of the _________________________________________________________________ a world-wide average. However, it has been estimated that the average annual dose in the United States from natural background radiation is higher, around 3 mSv or 300 mrems, because of a reevaluation of the quantities and effects of radon gas. KNIEF, at 88. For a brief discussion of radon gas, see below. 51. Tritium is a radioactive isotope of hydrogen. There is another isotope of hydrogen call deuterium (2H) or heavy hydrogen. Deuterium is not radioactive. LAMARSH, at 8; MEDICAL EFFECTS, at 391, 396. 52. T1/2 = 5730 years. 53. For example, Denver, Colorado or Bogota, Colombia. CHERNOBYL, at 23. 45  total average annual dose of natural radiation, i.e., a little over 2.0 mSv or 200 mrems annually Id. There are approximately 340 naturally-occurring nuclides on earth, and of these, about 70 are radioactive. LAMARSH , at 429. They are called primordial radionuclides because they have existed in the earth's crust since the earth was formed. Id. Those now present on earth have half-lives comparable to the age of the universe. MEDICAL EFFECTS, at 33. Accordingly, primordial radionuclides with half-lives of less than about 108 years can no longer be detected. Id. Primordial radionuclides with half-lives of more than 1010 years have decayed very little up to now. Id. Primordial radionuclides produce secondary radionuclides through the process of radioactive decay. There are three distinct chains of primordial radionuclides: (1) the uranium series, which originates with 238U; (2) the thorium series which originates with 232 Th; and (3) the actinium series, which originates with 235 U. Together, the parent of each chain and its respective daughter products contribute significantly to terrestrial irradiation. Id. Uranium is found in various quantities in most rocks and soils, and it is the main source of radiation exposure to people out-of-doors. CHERNOBYL, at 23. The uranium isotopes are alpha (a) particle emitters and, therefore, they do not contribute to gamma (g) ray exposure.54 MEDICAL EFFECTS, at 33. Since uranium isotopes are generally present in low concentrations, they do not contribute significantly to the internal alpha (a) ray dose delivered to humans. Id. However, since these isotopes are found in soil and fertilizers, they migrate into our food chain, and therefore, into our tissue. Id. at 35. Another significant source of terrestrial radiation exposure is radium-226 (226Ra)-- an isotope which originates in the uranium series -- and its daughter _________________________________________________________________ 54. Naturally occurring uranium consists of threeisotopes, 234U, 235U and 238U. Uranium-238, the parent of the uranium series is the most abundant isotope, present in the amount of 99.28%, and it is in equilibrium with 234U, which is present in the amount of 0.0058%. Uranium-235, present in the amount of 0.71%, is the parent of the actinium series. MEDICAL EFFECTS , at 33. 46  products. Radium-226, with a half-life of 1622 years, is an alpha (a) emitter and is present in all rocks, soils and water. Id. Radium is chemically similar to calcium and it passes through the food chain into humans because plants absorb it from the soil.55 The annual dose attributable to the intake of 226Ra is 7 microsieverts (Sv) or 0.7 mrem. Id. at 36. Approximately 95% of the world's people live in areas where the annual average dose from outdoor external radiation sources is about 0.4 mSv or 40 mrems. CHERNOBYL, at 24. However, there are areas in the world where people are exposed to very high levels of terrestrial radiation. For example, thorium-rich monozite sands in certain areas of Brazil and India also have exceptionally high levels of irradiation. LAMARSH, at 429.56 Radium-226 is also an important source of terrestrial radiation exposure because it decays to radon-222 (222Rn), a noble gas radionuclide with a half-life of 3.8 days that emits alpha (a) particles and contributes to gamma (g) radiation through its gamma-emitting descendants. Id. Radon is an odorless, colorless, nonreactive gas that poses no significant biological threat. Id. Alpha (a) particles emitted by radon outside the body do not penetrate skin. Id. However, the daughter elements formed as radon decays can be a significant source of natural irradiation and potential biological damage. CHERNOBYL, at 24. Once inhaled, the radon daughters may be deposited in the tracheo- bronchial tree. Id. Some of the radon daughters -- the polonium isotopes, 218 (radon A) and 214 (radon C 1) -- emit alpha (a) particles. 218Po (radon A) provides the major alpha (a) particle dose to the tracheo-bronchial tree, and it therefore poses an increased risk of lung cancer. C HERNOBYL, at 24. _________________________________________________________________ 55. In the human body, 70% to 90% of radium is found in bone. MEDICAL EFFECTS, at 35. 56. Similarly, in Guarapari, Meaipe and Pocos de Caldas in Brazil, exposure dose rates can be 100 times the norm, and in the coastal areas of Kerala and Tamil Nadu in India, exposure rates can be 1000 times higher than the norm. CHERNOBYL, at 24. 47  Because it is a noble gas, radon diffuses from its point of origin. LAMARSH, at 430. Moreover, because it is the immediate daughter product of the decay of radium-226 (226 Ra), it can be present in radium-bearing rocks, soils and home construction materials. Id at 429-30. Radon enters buildings primarily through the underlying and surrounding soils and, secondarily from building materials, outdoor air, tap water and natural gas. CHERNOBYL, at 24. Since concentration increases in enclosed spaces, radon concentration is much higher indoors than outdoors. MEDICAL EFFECTS, at 37-38. Radon is the largest contributor to terrestrial radiation because people spend most of their time indoors.57 Levels of radon in the air vary from place to place, season to season, day to day and hour to hour. Id. Both lead-210 (210Pb) and polonium-210 (210Po), which, as noted above, are decay products of radon-222 (222Rn), are introduced into the human body through inhalation as well as through the food chain. LAMARSH, at 429-30. 222Rn is a noble gas and therefore, tends to diffuse into the atmosphere where it can travel large distances before decaying into 210Pb. Id. at 430. 210Pb is not inert and attaches to dust and moisture particles in the atmosphere soon after it is formed. Consequently, it can be inhaled directly into the body or fall onto leafy vegetables or pasture grasses from where it can enter the food chain. Id. at 430, 433. Lead-210 does not lead to significant internal radiation doses because it is a rather weak beta (b) particle emitter. However, its daughter product, 210Po, is a powerful, highly-energetic alpha (a) particle emitter and it provides very significant doses of radiation. Id. at 431. Because both radionuclides can enter the body through ingestion, internal radiation exposure is influenced by dietary patterns. CHERNOBYL, at 24. For example, both radionuclides are present in seafood thus, in countries such as Japan, where seafood is a dietary staple, annual intakes of both radionuclides are significantly higher than in countries where seafood is not a staple. Id. Both _________________________________________________________________ 57. It is responsible for more than half of the natural radiation we are exposed to, i.e., 1.3 mSv per year or 130 mrems per year. CHERNOBYL, at 24. 48  radionuclides concentrate in lichens. Accordingly, people in the extreme northern hemisphere who eat the meat of animals that graze on lichens (caribou and reindeer) have levels about ten times higher than the norm. Id. Both 210Pb and 210Po are found on broadleaf tobacco plants, Id. at 433. Both of these radionuclides have also been detected in commercial tobacco products and in cigarette smoke. CHERNOBYL, at 24. There is a dispute within the scientific community as to whether background radiation produces stochastic effects. The International Commission on Radiological Protection assumes that stochastic effects may be induced by natural radiation and man-made radiation. ICRP 60, at 93. It has been inferred that about 3% of cancer deaths each year in the United States are attributable to background radiation, with 1.5 to 2% due to natural radiation, 0.5% to medical uses and 1% or less to occupational sources. See Luis Felipe Fajardo, Ionizing Radiation and Neoplasia, in NEW CONCEPTS IN NEOPLASIA AS APPLIED TO DIAGNOSTIC PATHOLOGY 99 (Cecilia M. Fenoglio-Preiser, Ronald S. Weinstein and Nathan Kaufman, eds., 1986). However, it has also been reported that natural background has not yet been proven to be cancer inducing, and, some scientists claim that natural background radiation does not cause cancer. Id. ii. Man made Radiation. Here, of course, we are most directly concerned with radiation from the nuclear power plant at TMI. It is undisputed that the production of electricity by nuclear power can add to the radioactivity in our environment. Irradiation occurs in the production of electricity, and in all stages of the fuel cycle, i.e., mining, fuel fabrication, transportation, reactor operation and reprocessing CHERNOBYL, at 26-27. However, under normal circumstances, and without considering the effect of nuclear power plant accidents, the overall impact of nuclear power generation on the total population is reported to be very small. MEDICAL EFFECTS, at 45. There are three major sources of man-made radiation other than nuclear power plants. These are: industrial processes other than nuclear power generation that also 49  use radionuclides, medical irradiation, and nuclear weapons testing. CHERNOBYL, at 24. Medical irradiation is generally divided into three categories: (1) diagnostic x-ray examinations; (2) the use of radiopharmaceuticals in nuclear medicine; (3) therapeutic applications of radiation. MEDICAL E FFECTS, at 47.58 Nuclear weapons testing occurs either above ground ("atmospheric testing"), or underground.59 Radionuclides released in atmospheric testing can enter the body directly or be deposited on the earth's surface from whence they may later be absorbed via the food chain, or be absorbed through by way of external radiation. MEDICAL EFFECTS, at 44. Generally, estimates of human exposure to fallout are more concerned with atmospheric (and more particularly stratospheric), fallout than with local or tropospheric fallout because radionuclides in the stratosphere result in fallout worldwide. Id. In fact, stratospheric particulate fallout accounts for most of mankind's worldwide exposure to fission products. Id. Fallout consists of numerous radioactive byproducts of atomic reactions. However, only four of these have half-lives of sufficient length to be of significant concern to present and future populations: 14C, with a half-life of 5730 years; 137Cs and 90Sr, both with a half-life of 30 years; and 3H, with a half-life of 12 years. CHERNOBYL, at 25. 14C provides almost two-thirds of the dose exposure because of the relatively short half-lives of the other three radionuclides. Id. The average annual dose to individuals from atmospheric testing is 0.01 mSv or 1 _________________________________________________________________ 58. The average annual dose due to medical irradiation is between 0.4 and 1 mSv or 40 to 100 mrems. CHERNOBYL, at 47. Of the three categories of medical irradiation, diagnostic x-ray examinations account for almost 95% of the total dose received. Id. 59. Atmospheric testing began in 1945. From then until 1980 there were more than 400 nuclear weapons tested in the atmosphere. CHERNOBYL, at 25. In 1963, the United States, the United Kingdom, and the former USSR entered into the Partial Test Ban Treaty, and undertook to cease atmospheric testing. However, France and China continued atmospheric testing. Id. All of the atmospheric tests released significant amounts of radioactive material into the environment. CHERNOBYL, at 47. 50  mrems. Id. There have been approximately 1300 underground nuclear weapons tests. MEDICAL EFFECTS, at 44. However, a well-contained underground explosion delivers little, if any, radionuclides to the environment, except for occasional venting. Id. Industrial processes, such as electricity production, mining, and the use of certain building materials and fertilizers produce above average concentrations of natural radionuclides. CHERNOBYL, at 25. Coal contains more radionuclides than other fossil fuels and burning coal produces a large amount of particulate emissions. M EDICAL EFFECTS, at 39. Other sources of industrial irradiation include certain consumer products, such as luminous timepieces, electronic and electrical devices, video display terminals, antistatic devices, and smoke detectors. MEDICAL EFFECTS, at 42. However, tobacco products probably contribute the greatest radiation dose of all consumer products. Id. at 43. It has been postulated that the radionuclides 210Pb and 210Po are responsible for the high incidence of lung cancer in smokers. BEIR V, at 19; LAMARSH, at 433. It is generally conceded that atmospheric weapons testing has contributed more to man-made radiation than nuclear power plants. Id. at 45. On average, the annual dose from all facets of the nuclear fuel cycle is less than 0.1% of that from natural radiation, CHERNOBYL, at 26, or less than 10 mSv or 1 mrem a year. KNIEF, at 88. In fact, it has been postulated that atmospheric releases of radionuclides from fossil fuel plants, especially coal plants without scrubber systems, may be greater than the releases of radionuclides from nuclear power plants. MEDICAL E FFECTS, at 45. Nevertheless, it is beyond dispute that nuclear power plants in general, and nuclear accidents in particular, can release harmful radioactivity into the environment. Irradiation occurs not only in the production of electricity but in all stages of the fuel cycle, i.e., mining, fuel fabrication, transportation, reactor operation and reprocessing CHERNOBYL, at 26-27.60 _________________________________________________________________ 60. Under normal circumstances, and without considering the effect of nuclear power plant accidents, the overall impact of nuclear power generation on the total population is reported to be very small. MEDICAL EFFECTS, at 45. 51  61. Charged particles and gamma (g) rays can also induce fission, but they are not significant for our purposes because neutron induced fission is the basis of commercial nuclear power, KNIEF, at 41, and it is that fission that occurred at TMI. Accordingly, before proceeding with our discussion of the District Court's application of Daubert to the expert testimony that was offered to prove that TMI-2 released radiation that caused the Trial Plaintiffs' neoplasms we will briefly discuss the operation of a nuclear power plant in an effort to better determine if Trial Plaintiffs proffered sufficient evidence to connect their injuries to the nuclear reactions that took place inside the nuclear generator at TMI-2. For purposes of assessing the Daubert challenges to the experts in this case, we will limit our discussion of nuclear fission to reactions initiated by neutrons.61 52Volume 2 of 4 Filed November 2, 1999 UNITED STATES COURT OF APPEALS FOR THE THIRD CIRCUIT Nos. 96-7623/7624/7625 IN RE: TMI LITIGATION LORI DOLAN; JOSEPH GAUGHAN; RONALD WARD; ESTATE OF PEARL HICKERNELL; KENNETH PUTT; ESTATE OF ETHELDA HILT; PAULA OBERCASH; JOLENE PETERSON; ESTATE OF GARY VILLELLA; ESTATE OF LEO BEAM, Appellants No. 96-7623 IN RE: TMI LITIGATION ALL PLAINTIFFS EXCEPT LORI DOLAN, JOSEPH GAUGHAN, RONALD WARD, ESTATE OF PEARL HICKERNELL, KENNETH PUTT, ESTATE OF ETHELDA HILT, PAULA OBERCASH, JOLENE PETERSON, ESTATE OF GARY VILLELLA AND ESTATE OF LEO BEAM, Appellants No. 96-7624 IN RE: TMI LITIGATION ALL PLAINTIFFS; ARNOLD LEVIN; LAURENCE BERMAN; LEE SWARTZ Appellants No. 96-7625 ON APPEAL FROM THE UNITED STATES DISTRICT COURT FOR THE MIDDLE DISTRICT OF PENNSYLVANIA (Civil No. 88-cv-01452) (District Judge: Honorable Sylvia H. Rambo)  ARGUED: June 27, 1997 Before: GREENBERG and McKEE, Circuit Judges, and GREENAWAY, District Judge* (Opinion filed: November 2, 1999) IV. NUCLEAR ENGINEERING A. Nuclear Reaction.62 The bulk of electricity generated in the United States is the result of thermal energy (i.e., heat) produced in either fossil-fueled boilers or nuclear power plants. ANTHONY V. NERO, JR., A GUIDEBOOKTO NUCLEAR REACTORS 3 (1979). Nuclear power plants generate energy through nuclear fission. Id. Nuclear fission provides nearly one hundred million times as much energy as the burning of one carbon atom of fossil fuel. KNIEF, at 4. Fission therefore has obvious advantages over fossil-fuel based energy production. It has been estimated that the complete fission of just one pound of uranium would release approximately the same amount of energy as the combustion of 6,000 barrels of oil or 1,000 tons of high-quality coal. NERO, at 4. However, the major disadvantage of the fission process is now painfully obvious. It requires mankind to harness and control one of the most awesome physical powers in the universe. In addition,