Full opinion text
McKEE, Circuit 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 .696 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 Untimejy.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 OPINION OF THE COURT I. INTRODUCTION These three appeals arise out of the nuclear reactor accident which occurred on March 28, 1979, at Three Mile Island in Dauphin County, Pennsylvania. 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 neoplasms 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, 113 S.Ct. 2786, 125 L.Ed.2d 469 (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 pretrial 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). II. PROCEDURAL HISTORY 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 Islapd nuclear power generating station in Dauphin County (“TMI-2”). Three Mile Island is a small island in ‘the Susquechanna River, approximately fifteen miles downstream from Harrisburg, Pennsylvania. Following the accident, thousands of personal injury and other non-personal injury claims were filed against the owners and operators of the nuclear facility. As noted, more than 2,000 plaintiffs filed claims for personal injuries 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). 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. 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” 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). 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. 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 du-plicative 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. 1:CV-88-1452, 1996 WL 506522, 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, 136 L.Ed.2d 678 (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.1994). The court also held that federal regulations 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 393-394. Upon defendants’ motion, the District Court certified the duty of care and causation questions for interlocutory appeal. 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, 116 S.Ct. 1034, 134 L.Ed.2d 111 (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, 113 S.Ct. 2786, 125 L.Ed.2d 469 (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 plaintiffs 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, who have been diagnosed with the listed illnesses, were chosen. 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 Plaintiffs 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. 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 building block of matter — and the physics of orbiting electrons. 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. Lamarsh, at 11. The nucleus has two constituent parts of approximately equal mass — the neutron and the proton. Bodansey, 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). “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 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 because once the element, X, is given, so is the atomic number, Z. Bo-daNSky, 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 “0”, consists of three isotopes, 160, 170, and 180. 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. Bodansicy, 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.” 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. La-marsh, 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”. 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. La-marsh, 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 than 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. La-MARSh, 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, Bennet, at 9; Bodansxy, at 352, with the lost energy equal to the difference in the energies of the two states. 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”). 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. 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”. Fred 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 x 1010 disintegrations per second. 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 (P) particle. Bodansky, at 354. The emission of these particles is often accompanied by the emission of one or more gamma (y) 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. Alpha (ct) 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. 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 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 (7) radiation. Id. Thus, the decay of a heavy radioactive isotope by alpha particle emission also produces gamma (7) radiation. Id. A beta (p) 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. La-marsh, 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 (p) particle. Id.) Bennet, at 13. Because beta (P) 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 (7) radiation. Id. In most cases, beta particles are negatively charged and are more properly designated as P' particles. Positive electrons, called “positrons” or p+ 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 (p) 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. However, the average energy of beta 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 (p) particle energy is shared with another particle called the neutrino. Bennet, at 13; Bo-dansicy, 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 0) particle decay usually occurs when a nuclide has an excess of neutrons. Bennet, at 13; Bodansky, at 358. A beta particle has greater penetrating ability than an alpha particle, BENNETat 21, with average penetration distances ranging from 0.1 to 1 g/em2, increasing with increasing energy. Bodansicy, 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 (7) radiation is electromagnetic radiation emitted in the form of photons by nuclei in excited states of energy. Except as noted below, gamma (7) emission is not a primary process of radioactive decay. Instead, it follows alpha (a) particle or beta (|3) particle emission. Gamma (7) rays do not have mass or charge, and they are therefore capable of much greater penetration of matter than alpha (a) or beta (p) particles. Bodansicy, 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 (7) ray emission are typically very short. Bodansicy, at 359. However, some nuclei have long-lived 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 (7) ray emission in a nuclei in an isomeric state is called an “isomeric transition”. Id. In such a case, gamma (7) ray emission appears to be the primary radioactive process of, rather than incident to, alpha (a) or beta (p) particle emission. Gamma ray emission can, however, ultimately be traced back to either initiating process. Bodansicy, 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. LamaRSH, 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. 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 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. La-maRsh, 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. 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 microscopic 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. Lamaesh, 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. Knief, at 70. The LET is of particular significance to an inquiry into the biological effects of radiation. Those effects depend 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; Bennet, at 20; Bodansky, at 354. Uncharged particles, such as gamma (y) 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 (7) rays can interact with matter in a variety of ways, there are, for purposes of our analysis, three important types of interaction between gamma (7) radiation and matter — the “photoelectric effect”, “pair production” and “Compton scattering.” Bennet, at 21. Because very short-range forces govern electromagnetic mechanisms, a gamma (7) 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 (7) ray energies, Bennet, at 199, the gamma (7) ray interacts with the entire atom, the gamma (7) ray disappears and one of the atomic electrons is ejected from the atom. Lamarsh, at 79. As a result, the energy of the gamma (7) ray or photon is converted completely to kinetic energy of an orbital electron. Knief, at 71. If the gamma (7) 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 (7) rays and only in the vicinity of a heavy nucleus. Id. at 80; Bennet, at 21. The gamma (7) ray is annihilated; and an electron pair — a positron and a negatron — is created. La-marsh, at 80. When this occurs the energy of the gamma (7) ray converted to mass, and kinetic energy of the electron pair. Knief, at 71. Once they are formed, the positron and 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 (7) 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 (7) ray, Id. at 81, thus reducing the energy level of the reaction. Knief, at 71. Since the gamma (7) 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 (7) 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 (7) are referred to as “low LET radiation.” La-marsh, 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 “Ci-iernobyl”). Originally, the amount of radiation éxposure for X- and gamma (7) 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. Alternatively, a roentgen can be defined 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. 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. 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 Systems International d’Unites (“SI”) 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 (lGy = 100 rads), or one rad equivalent to 10 milligrays (1 rad = 10 mGy). Medioal 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 (7) 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. Lamarsh, 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.; Knief, at 73. For example, X-rays and gamma (7) rays have a Q of 1, beta (p) particles have a Q of 1 to 1.7, depending on their energy, and alpha (a) particles have a Q of 20. Chernobyl, 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. La-maesh, at 404. Thus, if the radiation is gamma (7) 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. 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 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 Protection 94 (1990)(herein-after “ICRP 60”). The initial evidence was mainly noted from the effect of ionizing radiation on human skin. 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. 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 an-kylosing spondylitis, cervical cancer and tinea capitis. National ReseaRch Council, Committee on the Biological Effects of Ionizing Radiations, Health Effects of ExposuRE to Low Levels of Ionizing Radiation 2(1990) (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. 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, H20+, and an electron. The electron can be trapped and produce a hydrated electron, eaq. BEIR V, at 12. However, the ionized water molecule, H20+, reacts with another water molecule to produce a free radical called the “hydroxyl radical, OH.” Id. 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 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. 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. Medioal 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. Medioal 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 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 aré 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. Lamaesh, 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. Id. Cell death usually becomes apparent within a few hours or days after irradiation. Id. at 97. 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. Cheknobyl, 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