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, No. 96-7623 in Re: Tmi Litigation All 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, No. 96-7624 in Re: Tmi Litigation

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)[Copyrighted Material Omitted][Copyrighted Material Omitted][Copyrighted Material Omitted][Copyrighted Material Omitted][Copyrighted Material Omitted][Copyrighted Material Omitted]

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

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

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

Before: Greenberg and McKEE, Circuit Judges, and Greenaway, District Judge*

                           TABLE OF CONTENTS
I. INTRODUCTION                                                         622
II. PROCEDURAL HISTORY                                                  623
III. SCIENTIFIC BACKGROUND                                              629
 A. Overview of Relevant Principles of Nuclear Physics                  629
    1. Atomic and Nuclear Structure                                     629
    2. Radioactivity                                                    632
    3. Ionizing Radiation                                               634
    4. Radiation Quantities and Units                                   636
    5. Health Effects of Ionizing Radiation                             638
       i. Deterministic Effects                                         640
      ii. Stochastic Effects                                            642
    6. Radiation in the Environment                                     644
       i. Natural Radiation                                             644
      ii. Man-made Radiation                                            647
IV. NUCLEAR ENGINEERING                                                 648
 A. Nuclear Reaction                                                    648
 B. The Operation of Nuclear Power Plant                                651
 C. Barriers to Release of Radioactive Materials into the Environment   655
V. THE ACCIDENT AND ITS AFTERMATH                                       655
 A. The Accident at TMI-2                                               655
 B. Radioactive Materials Released to the Environment                   657
 C. Pathways of Exposure to Radioactive Materials                       658
VI. LEGAL DISCUSSION                                                    659
 A. The Trial Plaintiffs' Appeal                                        659
    1. Background                                                       659
    2. Standards Governing the Admissibility of Scientific Evidence     662
    3. Trial Plaintiffs' Dose Exposure Expert Witnesses                 666
       i. Ignaz Vergeiner                                               666
          a. Qualifications                                             666
          b. Vergeiner's Opinion.                                       667
          c. Discussion and Conclusions                                 667
       ii. Charles Armentrout and Victor Neuwirth                       672
          a. Qualifications                                             672
          b. Armentrout's Observations and Experiences                  672
          c. Discussion and Conclusion                                  673
          d. Neuwirth's Soil Sample Analyses and Armentrout's Dose
               Estimates.                                               674
          e. Discussion and Conclusion                                  675
       iii. James Gunckel                                               677
          a. Qualifications                                             677
          b. Gunckel's Opinion                                          678
          c. Discussion and Conclusions                                 680
       iv. Vladimir Shevchenko                                          683
          a. Qualifications                                             683
          b. Shevchenko's Tree Study                                    684
          c. Discussion and Conclusions                                 686
          d. The Cytogenetic Analysis                                   688
          e. Discussion and Conclusions                                 690
       v. Gennady Kozubov                                               693

          a. Qualifications                                             693
          b. Kozubov's Opinion                                          693
          c. Discussion and Conclusions                                 694
       vi. Olga Tarasenko                                               695
          a. Qualifications                                             695
          b. Tarasenko's Opinion                                        695
          c. Discussion and Conclusions                                 697
       vii. Bruce Molholt                                               698
          a. Qualifications                                             698
          b. Molholt's Opinions                                         699
          c. Discussion and Conclusions                                 701
       viii. Sigmund Zakrzewski                                         704
          a. Qualifications                                             704
          b. Zakrzewski's Opinion                                       704
          c. Discussion and Conclusions                                 705
       ix. Theodor Sterling                                             706
          a. Qualifications                                             706
          b. Sterling's Opinion                                         706
          c. Discussion and Conclusions                                 707
       x. Steven Wing                                                   708
          a. Qualifications                                             708
          b. Wing's Mortality Study                                     709
          c. Discussion and Conclusions                                 710
          d. Wing's Cancer Incidence Study                              711
          e. Discussion and Conclusions                                 712
       xi. Douglas Crawford-Brown                                       713
          a. Qualifications                                             713
          b. Crawford-Brown's Opinion                                   714
          c. Discussion and Conclusions                                 714
    4. Effect of the Exclusion of Wing's Lung Cancer Testimony          716
    5. Exclusion of Experts' Submissions as Untimely                    717
    6. Conclusion                                                       722
 B. The Non-Trial Plaintiffs' Appeal                                    723
 C. The Monetary Sanctions Appeal                                       728
 D. Reassignment Upon Remand                                            728
VII. CONCLUSION                                                         729

These three appeals arise out of the nuclear reactor 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 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 the first 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).

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 claims4 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

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, 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. § 2014(h). The Act also provided for consolidation of such actions, including those already filed, in one federal district court. 42 U.S.C. § 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 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... shall 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. § 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. § 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 that § 20(b), read in conjunction with § 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 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, 519 U.S. 1077, 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, 904 F.Supp. 379, 395 (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 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. 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 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 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.

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 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 x 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 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 notationAZ 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 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, and¹⁸O. 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. 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. BENNET, 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. BODANSKY, 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. BODANSKY, 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 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".