Allen v. United States

MEMORANDUM OPINION

In a sense this case began in the mind of a thoughtful resident of Greece named Democritus some twenty-five hundred years ago. In response to a question put two centuries earlier by a compatriot, Thales, concerning the fundamental nature of matter, Democritus suggested the idea of atoms. This case is concerned with atoms, with government, with people, with legal relationships, and with social values.

This case is concerned with what reasonable men in positions of decision-making in the United States government between 1951 and 1963 knew or should have known about the fundamental nature of matter.

It is concerned with the duty, if any, that the United States government had to tell its people, particularly those in proximity to the experiment site, what it knew or should have known about the dangers to them from the government’s experiments with nuclear fission conducted above ground in the brushlands of Nevada during those critical years.

This case is concerned with the perception and the apprehension of its political leaders of international dangers threatening the United States from 1951 to 1963. It is concerned with high level determinations as to what to do about them and whether such determinations legally excuse the United States from being answerable to a comparatively few members of its population for injuries allegedly resulting from open air nuclear experiments conducted in response to such perceived dangers.

It is concerned with the method and quantum of proof of the cause in fact of claimed biological injuries. It is concerned with the passage of time, the attendant diminishment of memory, the availability of contemporary information about open air atomic testing and the application of a statute of repose.

It is concerned with what plaintiffs — laymen, not experts — knew or should have known about the biological consequences that could result from open air nuclear tests and when each plaintiff knew or should have known of such consequences.

It is ultimately concerned with who in fairness should bear the cost in dollars of injury to those persons whose injury is demonstrated to have been caused more likely than not by nation-state conducted open air nuclear events.

The complaint in this action alleges that each plaintiff, or his predecessor, has suffered injury or death as a proximate result of exposure to radioactive fallout that drifted away from the Nevada Test Site and settled upon communities and isolated populations in southern Utah, northern Arizo *258 na and southeastern Nevada. Each of the plaintiffs or their decedents resided in that area. Each claims serious loss due to radiation-caused cancer or leukemia. Each asserts that the injury suffered resulted from the negligence of the United States in conducting open-air nuclear testing, in monitoring testing results, in failing to inform persons at hazard of attendant dangers from such testing and in failing to inform such persons how to avoid or minimize or mitigate such dangers.

A. JURISDICTION

This Court has jurisdiction of this action pursuant to 28 U.S.C. § 1346(b) (1976) and the Federal Tort Claims Act, 28 U.S.C. §§ 2671-2680 (1976). Venue of this action is proper pursuant to 28 U.S.C. § 1402(b) (1976). 1 The Federal Tort Claims Act (FTCA) is the exclusive legal remedy for claims against the United States “for money damages ... for ... personal injury or death caused by the negligent or wrongful act or omission of any employee of the Government while acting within the scope of his office or employment, ... ”' This action was tried to the Court, without a jury, pursuant to the requirement of 28 U.S.C. § 2402 (1976) that “[a]ny ■ action against the United States under section 1346 shall be tried by the court without a jury, ...” See O’Connor v. United States, 269 F.2d 579 (2d Cir.1959). 2

B. NATURE OF THE ACTION

This action is a consolidation of the individual claims of the 1,192 named plaintiffs in this lawsuit. This is not a class action. Cf. Annot., 48 A.L.R.Fed. 860 (1980). Trial was held in this action beginning September 14, 1982 and concluding with final arguments on December 17, 1982. The trial encompassed 24 of the claims in their entirety. Pursuant to the suggestion of the court these cases were selected by plaintiffs’ and defendant’s counsel as “bellwether” cases. The effort was to provide a selection of “typical” cases which when decided and reviewed may provide a legal and factual pattern against which the remaining issues in the pending cases may be subsequently matched.

The trial was conducted as well so as to make a full and complete record concerning legal, historic, and scientific matters common to all of the 1,192 plaintiffs with the idea in mind of avoiding future duplication of effort. See Park Lane Hosiery Company, Inc. v. Shore, 439 U.S. 322, 99 S.Ct. 645, 58 L.Ed.2d 552 (1979). Other than as noted in this opinion, this court has not decided the remaining issues in the claims of the more than 1,100 plaintiffs that are still pending in the consolidated case.

This opinion decides claims of individuals, each with his own history and relationship to the open air nuclear tests. It fully decides 24 separate cases, tied together by common legal, historic and scientific threads of unique importance.

C. THE TRIAL

This action has been pending since August 30, 1979. It has been the subject of extensive pre-trial motions, dealt with on a preliminary basis by this Court’s earlier opinion. See Allen v. United States, 527 F.Supp. 476 (D.Utah 1981). That opinion in a general way defined the framework for the trial that followed.

During the course of trial, this court received into evidence the testimony of 98 witnesses as well as more than 1,692 documentary exhibits. 3 The evidence provides *259 testimony of witnesses ranging from those who participated in the testing program and related operations to highly trained and gifted “experts” offering conflicting opinions, to claimants who seek solace for their test-blamed sorrow.

The record contains historic documents, internal agency memoranda newly declassified, agency directives and correspondence, epidemiological studies, scientific texts and articles, as well as extracts from news media of the day and public information pamphlets.

D. THE PROBLEM OF UNCERTAINTY

We all seek to simplify and to order. The mind eschews the uncertain. We strain for certainty and perfect knowledge in an infinitely complex and dynamic universe. In doing so, we often fail to distinguish between those things which we directly experience, see, feel, hear, taste, smell — facts we experience — from those facts we infer. Each is a form of knowledge. Each we say we know. But we must be constantly aware of the nature of that which we say we “know”.

For example, we “know” of the existence of the atom. We “know” of the existence of gamma rays. We have never seen an atom or a gamma ray. We infer that atoms exist. The atom is a mind-created abstract model which provides a convenient, coherent and consistent explanation of an immense collection of perceived effects. 4 It is a model fashioned by many minds after a meticulous sifting of the observed and the reported. 5 But, we remain uncertain still of our scientific certainties.

This court has attempted to formulate an ordered theory of decision. While the effort lacks the mathematical purity of physical theory, it is the judicial resolution of the questions raised by this case with which the court is concerned. The theory of decision melds the method of science with principles of law and public policy.

In doing so, the court endeavors to follow the suggestions offered in a recent address by Chief Judge Howard T. Markey of the U.S. Court of Appeals for the Federal Circuit:

The differences between the judicial and the scientific-technological processes are profound and pervasive. Failure to recognize that difference has led to judicial expressions of frustration and an unfortunate tendency to rest judicial decisions on current, and often transient, “truths” and “facts” of science and technology. The purpose and function of science is to learn physical facts____

The purpose and function of law is to resolve disputes and to facilitate a structure for the organization of a just society — in a word, to provide justice.

Science normally evolves a new, general physical principle from hypotheses proven by numerous specific experiments. The normal judicial process is precisely the reverse, for, when properly conducted, it applies an existing, generally accepted moral or social value — an eth *260 ical principle — a rule of law — to a specific problem____

Judges and lawyers must approach with great care, the idea that court decisions can be justified solely on the findings of science, lest the quest for justice be lost along the way.

For the particular “scientific truth” relied upon may prove transient indeed.

s}c :js :J: s¡‘ j}: ;}:

Markey, “Needed: A Judicial Welcome for Technology,” 79 F.R.D. 209, 210-211 (1979). Judge Markey highlights a premise of this court’s theory of decision:

The first need, then, is to view technological evidence as merely one evidentiary element in the judicial matrix of decision and not necessarily as the sole justification for the judge’s legal decision.

Id. at 211 (emphasis in original).

At the core of this case is a fundamental principle — a time-honored rule of law, an ethical rule, a moral tenet:

[T]he law imposes [a duty] on everyone to avoid acts in their nature dangerous to the lives of others.

Devlin v. Smith, 89 N.Y. 470, 477, 42 Am.Rep. 311 (1882); see also Thomas v. Winchester, 6 N.Y. 397, 57 Am.Dec. 455 (1852). The more particularized rules of negligence and proximate cause as a basis for liability which are applied in the body of this opinion are rooted in this principle of duty. In this case, as in any other case in tort law, the answer to the ultimate question: “Who should bear the burden of the risks created by the defendant’s conduct?” is ultimately a question of policy and of public values.

In the law, as in science, one always faces uncertainty. 6 This court, faced with the duty of judgment in this case, does not have the luxury of the zealous absolutists who “know beyond doubt” that each and every cancer in the Great Basin is the result of open air atomic testing, or of their absolutist counterparts who “know beyond doubt” that none resulted. The court is disciplined by the record and the application of rules of law.

The court’s findings of fact have a certainty that is relative to the evidence presented to the court by others. They are not fixed in absolute terms. Judicial determination of facts in this case is indistinguishable from fact-finding in other cases no matter how “complex” the facts here might be. 7

Thus, this opinion speaks in terms of “natural and probable” consequences, “substantial” factors and things “more likely than not.”

In the pragmatic world of “fact” the court passes judgment on the probable. Dispute resolution demands rational decision, not perfect knowledge.

II. BACKGROUND: BASIC PRINCIPLES OF RADIATION AND NUCLEAR PHYSICS

Evaluation of the risks and consequences of exposure to atomic radiation in this case demands some familiarity with the concepts of radiation physics and its basic language. Such familiarity is a prelude to the knowledgeable application of rules of law.

It does not come easily. It did not come easily for the court.

The effort of the court has been to set forth as best it can the peculiar language and pertinent concepts of radiation physics as the court understands them from the record, to enable those concerned to under *261 stand the legal relationships of the parties as found by the court and the legal consequences of party action.

The synopsis found in the next section of this opinion is part of the judicial effort to understand this case. It does supply some of the reasons why this court has found as it has found and has decided as it has decided. It does supply some of the reasons why the rules of law discussed and applied in subsequent sections have been applied as they have.

A. Scientific Notation and Mathematical Prefixes

Nuclear physics explores the universe using numbers and quantities which range from the extremely large to the infinitesimally small. To simplify the task of using numbers larger than 10 or less than 1, a shorthand system of expression has been devised that relies upon exponential powers of ten. Scientific notation, as this system is called, works in this fashion: Consider, for example, the number 100. One hundred is one way of expressing the quantity 1 x 100, or 1 x (10 x 10). Using exponents, this expression is shortened to 1 X 102, which still means 100. Similarly, 1,000 (1 X 10 X 10 X 10) may be expressed as 1 X 103 (or simply 103) one million (1,000,000) as 1 x 106 (or 106) and so forth. More complex numbers may be expressed in this fashion:

6,205,000,000 = 6.205 X 109

1,899,205 = 1.899205 X 106

89,450,000,000,000 = 8.945 x 1013

Decimal fractions may be expressed in scientific notation as well. For example, 0.01 equals Vioo or, as we have seen Vio2. The common form of stating this fraction in scientific notation is 1 X 10~2, or 10~2. Thus a negative exponent indicates a fractional quantity while a positive exponent indicates a value greater than 1. 8

Consider the following examples:

(1) 0.0032 = 32/10,000 = 32/104 = 32 x 10~4 or, more commonly, 3.2 x 10“3

(2) 0.65 = 65/100 = 65/102 = 65 X 10~2 or 6.5 X 10"1

(3) 0.000042 = 42/1,000,000 = 42/10"6 or 4.2 X 10~5

Scientific notation proves extremely useful in performing mathematical operations involving very large or very small numbers. Multiplication is accomplished through simple multiplication of the initial terms and through addition of the exponential terms. For example,

(1) 6,500,000 X 42,120,000,000 = ?

Switching to scientific notation gives us

(6.5 X 106) x (4.212 X 1010) = ?

which is computed in this fashion:

(6.5 x 4.212) x 10<6 +10> = 27.378 X 1016

or, expressed in simplest form, 2.7378 x 1017. This expression seems far simpler to write than 273,780,000,000,000,-000, which is the more conventional form. Fractions are multiplied in the same fashion:

(1) 1.2 X 10-4 X 6.88 X 10"12 = ?

(1.2 x 6.88) X 10(H) 1 H2)) = 8.256 X 10"16,

a number expressed conventionally as .0000000000000008256.

Division of numbers expressed in scientific notation is accomplished in a parallel way:

(1) 6.2 x 106 4- 3.8 x 102 = ? (6.2 4- 3.8) X 10<6-2> = 1.6315789 X 104

(2) 3.2 X 1018 4- 4.5 X 1011 = ? (3.2 -4- 4.5) X 10<18-n> = .71111 X 107 or 7.1111 X 106 — a short way of saying 7,111,100.

(3) 1.62 X 10-2 4- 6.04 x 106 = ? (1.62 4- 6.04) x 10«-2)-6> = .2682 X 10"8 or 2.682 x 10“9 — a short way of writing 0.000000002682.

Numbers such as these are commonplace in nuclear physics. For example, Planck’s Constant, a fixed number defining the proportional relationship between the frequency of a light wave and its energy, is ex *262 pressed as 6.6261965 X IO-34, a term far more easily handled in computations than is 0.0000000000000000000000000000000006-6261965, its conventional equivalent. 9 Scientific notation makes it possible for a small electronic calculator with an eight-digit or ten-digit display to calculate numbers ranging from 1099 to 10~99. Mathematical operations beyond either limit of that range have no practical value; nothing in our experience is either that large or that small. 10

The mathematics used in nuclear physics is simplified for practical purposes through use of scientific notation. Another system of simplification involves units of measurements routinely used by humans in describing matter, energy and their interactions. At this point in history, science maintains a preference for units in the metric system. Mass is measured in grams, length in units called meters, volume in litres, energy in units such as ergs or joules. Often, calculations are made in terms of very large or very small quantities — thousands of units or infinitesimal fractions of units. One may be working with a thousand grams or a million grams or with a billionth of a gram. A system of word prefixes has been devised under the International System of Units to adjust units to more closely relate to the actual quantities being utilized. Table 1 lists these prefixes and their definitions.

TABLE 1. Prefixes for the Units in the International System 11

[[Image here]]

Thus, when one is working with 6 x 103, or 6,000 grams, one is also working with 6 kilo grams. Likewise, if the quantity is 0.000000082 grams, or 8.2 x IO"8 g, a more workable expression may be 8.2 x 10~2 or .0820 micro grams (yg). As will be seen, it is not uncommon to speak of micrograms, or pico curies (a tiny unit of radioactivity) of fallout material deposited in human bodies, or of kilograms of material, or mega curies of fallout radioactivity generated by detonation of a nuclear weapon. 12 The difference between a picocurie of radioactivity and a megacurie of radioactivity is a factor of 1018 or 1,000,000,000,000,000,- *263 OOO. 13 Yet both units are meaningful to the evidence in the record before this court. See Part IV(A), infra.

Simply by referring to Table 1, one can determine what multiple or fraction of a standard unit is being discussed in the text. Quick reference to Table 1 prefixes will aid the reader in identifying the units used and in making a meaningful comparison of quantities.

B. The Atom: Protons, Neutrons and Electrons

After centuries of careful observation, our best answer to Thales’ 2,500-year-old question “What is the world made of?” seems to be that all matter is composed of atoms. See G. Amaldi, The Nature of Matter (1966). Atoms are very tiny packages of mass which have specific physical qualities. 14 In the natural world around us, science has identified 92 species of atoms commonly referred to as elements. Each element has unique physical and chemical properties. Each element’s atoms differ slightly in structure and composition from the atoms of any other element. Some elements are familiar: copper, iron, oxygen, gold, carbon, calcium and two dozen others are well known as part of our own chemical makeup, or as part of the everyday world around us. Others, such as praseodymium, rubidium, and polonium, are far more obscure. Each, however, represents a different type of atom.

In addition to the 92 “natural” elements, scientists have produced a dozen more “synthetic” elements, such as plutonium, which are heavier, and often more unstable and short-lived than their “natural” brethren. 15 A complete list of the known chemical elements is found in Table 2.

[[Image here]]

*264 [[Image here]]

The differences between atoms of different elements are accounted for by variations in their composition and structure. All atoms are thought to be composed of three types of smaller particles: protons, neutrons and electrons. A proton is a tiny particle with a mass of approximately 1.672 X 10~24 gm, or 1.007 atomic mass units. 16 Each proton carries a positive electric charge. 17 An electron is a particle with a negative electric charge equivalent to that of a proton but with 1/1837 the mass of a proton, or 5.5 x 10-4 amu. An electron has a diameter of approximately 1 x 10~12 cm. *265 A neutron is a subatomic particle having no electric charge (hence the name) yet having a mass of l.0087 amu — slightly heavier than a proton. An atom of a particular element represents a specific combination of protons j neutrons and electrons.

Far from being randomly distributed within an atom, these particles are ordered according to specific principles of structure:

(1) Each atom contains a nucleus at its center;

(2) Protons and neutrons are located within the nucleus;

(3) The nucleus is tiny in relation to the atom itself, comprising about 1/100,000th of the volume of the atom, yet containing almost all of its mass;

(4) Electrons orbit the nucleus in constant motion, and in patterns better described using the physics of standing waves; 18

(5) An electrostatically neutral atom is one with an equal number of electrons and protons; an atom with an imbalance of protons and electrons will itself act as a charged particle, called an ion. Ions — electrically charged atoms — are often far more reactive with other atoms than are neutral, unionized atoms;

(6) Electrons are distributed in the space around the nucleus in stable orbitals, which correspond to a discrete amount of energy, often called an energy state;

(7) Only certain energy states, or orbitals, are allowed in atoms of a given element;

(8) An electron may move from one energy level to a higher energy level, by absorbing energy from an outside source in an amount equal to the difference between the two energy levels; an electron may fall to a lower energy level by emitting energy in the amount of the difference between the two levels. The energy is emitted in the form of a photon. 19

An electron may absorb energy, (i.e., become “excited”) to a degree sufficient to allow it to leave the atom altogether. This phenomenon is called ionization, and is the key to innumerable chemical reactions.

The simplest element is hydrogen, whose atoms consist of a single proton in the nucleus and a single electron in the surrounding orbitals. The number of protons in the nucleus determines the number of electrons in the atom’s orbital shells, which has significant effect on the atom’s chemical characteristics. The number of protons is often referred to as the atomic number and is identified in the literature by the symbol Z. An element’s atomic number determines its place in an important scheme of classification known as the Periodic Table. See Table 3.

*266 [[Image here]]

From: Handbook of Chemistry and Physics (50th ed. Weast 1969).

*267 The elements in each column grouping, or period, share similar electron structures, physical and chemical properties. See I. Asimov, Understanding Physics: The Electron, Proton, and Neutron 13-18 (1966); C. Hammond, “The Elements,” in Handbook of Chemistry and Physics, pp. B-2 to B-40 (64th ed. Weast 1983).

In addition to the atomic number, atoms are described according to atomic weight, symbolized by the letter A, which quantifies the total mass of an atom as expressed in atomic mass units (amu). The atomic weight of hydrogen is approximately 1.00797 amu, the single proton being the source of almost all of its mass. Heavier elements have nuclei containing neutrons as well as more protons. Helium, for example, has two protons and (usually) two neutrons in its nucleus, giving it an atomic number (Z) of 2 and atomic weight (A) of approximately 4.0026. While varying the number of protons will change the atom from one element to another, varying the number of neutrons changes the atomic weight of the atom without radically affecting its physical or chemical properties. Atoms of the same element which have different numbers of neutrons in the nucleus are referred to as isotopes of the element. Hydrogen, for example, has three isotopes: the most common form, protium, has no neutrons; deuterium, or heavy hydrogen, has one proton and one neutron; tritium, the heaviest, has two neutrons for each proton. Isotopes are often referred to by an abbreviation of their atomic weights called a mass number. Radium (Z = 88, A = 226.054) becomes simply radium 226 or 226Ra. Radium 224 (A = 224.0202) is another isotope of the same element having two less neutrons. In lighter elements the number of neutrons and protons in the nucleus tends to be equal, or nearly so. In the heavier elements toward the bottom of the Periodic Table, neutrons outnumber protons. Lead, for example, has 82 protons (Z = 82) and an average of 115 neutrons (A = 207.19) in its nuclei, compared to Calcium (Z = 20, A = 40.08) or Neon (Z = 10, A = 20.183).

C. Radiation and Radioactivity

Perhaps the simplest definition of radiation is the one most easily understood: radiation is a transfer of energy through space (or some other accommodating medium). Usually energy is radiated in the form of light or heat, though as we shall see, energy can be radiated through emission of particles having momentum. 20

Despite its outward appearance, light— or, more broadly, electromagnetic radiation — is not transmitted as a continuous flow of energy. When light is radiated, its energy is packaged in discrete units, 21 tiny bundles of energy called photons. Careful observation has disclosed that photons have some properties which are best explained if they are considered as waves; other properties are best explained if photons of light are thought of as particles. The energy of a particular photon, or light wave-particle, is related to its frequency as follows: E = Av Where E is energy (in ergs), v is the frequency (in Hertz) and h is a number known as Planck’s Constant. See note 9, supra. The relationship may also be described in terms of wavelength.

E = «4-)

E is energy

h is Planck’s constant

c is the speed of light

K is the wavelength

In short, the higher the frequency (or the shorter the wavelength) of light, the greater its energy. Visible light falls roughly midway on the spectrum of light energy with wavelengths [ X ] ranging from *268 7 x 10~5 cm for red light through 4 x 10~5 cm for violet. Wavelengths longer than those for visible light fall toward the infrared end of the spectrum: radar waves, radio waves, and microwaves have photons of less energy than visible light. Light wave-particles of greater energy range from ultraviolet light having sufficient energy to cause sunburn cm) to x-rays, gamma rays (X" 10 ~8 to 10~10cm) and high energy cosmic rays (A> 10~12 cm) which are of particular interest to this lawsuit.

Differences in photon energy are crucial. We are constantly awash in an invisible ocean of radio waves which pass by — and through — our bodies with no perceivable harmful effect. However, exposure to gamma rays, which easily may be one-hundred trillion (1014) times more powerful than broadcast radio waves, raises serious human health concerns. See Part IV, infra.

At the end of the last century, scientists in Europe led by Wilhelm Roentgen discovered basic techniques for producing high energy photons — “x-rays”, Roentgen called them — in the laboratory. By bombarding a metal plate within a sealed glass vacuum tube with high-voltage electrons, invisible radiation was produced which would cause certain chemicals to fluoresce brilliantly, and which could fog or darken photographic plates wrapped in paper, or even concealed within a box. See S. Glasstone, Sourcebook on Atomic Energy 48-51 (2d ed. 1958); I. Asimov, Understanding Physics: The Electron, Proton and Neutron 33-35 (1966). In 1896, the French physicist Henri Becquerel discovered that the same kind of penetrating radiation emanated from uranium salts. 22 In 1898, Marie Curie gave this phenomenon of constant emission of penetrating, ionizing radiation the name radioactivity. S. Glasstone, Sourcebook on Atomic Energy, at 53; see Mme. Sklodowska-Curie, 126 Comptes Rendus 1101 (1898). One of the first properties observed in both x-rays and radioactive substances was the induction of an electrical charge in the air surrounding an x-ray tube or immediately in contact with a sample of radioactive material. This ionizing effect enabled early researchers to detect such radiation using very simple devices. “[T]o detect nuclear particles we detect ionization.” E. Pollard & W. Davidson, Applied Nuclear Physics 43 (1942) (emphasis in original). Radiation detection and measurement techniques are still very heavily dependent upon this particular quality. See e.g., N. Tsoulfanidis, Measurement and Detection of Radiation (1983). 23 As we shall see, the adverse health effects of exposure to radiation are also a product of ionization. See Part IV infra.

D. Ionizing Radiation: Alpha, Beta, and Gamma Rays.

Early research work by Ernest Rutherford and others using heavy radioactive elements such as radium, polonium, thorium and uranium, disclosed that ionizing radiation emanating from radioactive materials could be resolved into three different types: alpha rays (a), beta rays (/?) and gamma rays (y). Application of a strong magnetic field to a stream of ionizing radia *269 tion emitted by a sample of radium salts readily deflected beta rays in a fashion indicating that beta radiation carries a negative charge. See Fig. 1.

RADIO-ACTIVE SUBSTANCES. 33

[[Image here]]

Fig. 1. Mine. Marie Sklodowska Curie, Radioaclire Subslancen, thesis presented to the Faculty of Sciences, Paris, !!)():) (pap. reprint ed. 1961), at 3!I-;54.

Less easily deflected in the opposite direction were alpha rays, which were deduced to have a positive electrostatic charge and greater momentum than beta *270 rays. Gamma rays passed undeflected by the strongest magnetic fields; their highly penetrating qualities led researchers to conclude that gamma rays and x-rays were very similar (which they are). See e.g., J. Cork, Radioactivity and Nuclear Physics 11 (1947). Soon it was determined that beta rays exhibited all the properties of high-energy electrons, while alpha rays were identified as consisting of the nuclei of helium atoms stripped of both outer electrons. Both gamma rays and x-rays were found to consist of very short wavelength high energy photons. 24

Of crucial importance was the discovery that radioactivity is the product of internal processes within the nucleus of the atom rather than the result of excitation by some undetected outside source of energy. Radioactivity properties are unaffected by external forces, such as heat, light or pressure, or by any chemical reaction. 25 Instead, they operate according to specific principles of nuclear physics.

The basic principle finds simple expression in the work of Pollard and Davidson: “This process, the passage from one nearly stable nucleus to one which is stable, is the underlying process of radioactivity.” Applied Nuclear Physics 102 (1942). Recalling that the nuclei of atoms are made up of various combinations of protons and neutrons, and that within atoms of a given element, the ratio of neutrons to protons may vary from isotope to isotope, careful observation of radioactive properties reveals that some proton/neutron ratios tend to be far more stable than others. Radioactivity represents the mechanism of internal adjustment by which less stable nuclei transform their composition into a proton/neutron ratio having greater stability. Emission of an alpha particle, for example, lightens the nucleus in evenhanded fashion; the numbers of neutrons and protons are each reduced by 2. Radioactive transformation by a-particle emission is observed most often in the decay of heavy elements (Z > 84), 26 such as uranium (Z = 92, A = 238), which ultimately “decay” to the very stable nuclear structure found in lead 206 (Z = 82, A = 206):

284Po-* 282Pb + 2He ( «-particle)

A nucleus which has a greater ratio of neutrons to protons than is found in more stable forms may emit a beta particle (/?-) — a high energy negative electron — as one of the neutrons is transformed into a proton. Strontium-90, with 38 protons and 52 neutrons, is radioactive. It decays by ,6-emission into Yttrium-90, with 39 protons and 51 neutrons. Yttrium-90 in turn decays into Zirconium-90 by /6-emission. Zirconium-90 with 40 protons to 50 neutrons, is the stable, naturally predominate isotope of that element. Radioactivity ceases.

90c /6 90,. /6 90„ , , , . , 38Sr--► 39Y -u — > 40Zr (stable)

*271 Atoms with an overabundance of protons may decay by emitting a positively charged electron, or positron (/3+), or by capturing an electron from a nearby orbital. Either process reduces the number of protons and increases the number of neutrons by 1.

For example,

U80 -> (stable) + /? + (positron)

When the radioactivity properties of the nuclides 27 are plotted on a graph of numbers of neutrons (N) and protons (Z), a pattern emerges. See Fig. 2.

[[Image here]]

Fig. 2. L). Halliday, Introductory Xu clear Physics 9 (1950).

*272 Radioactive decay enhances nuclear stability not only by adjusting the total number of particles, but also by carrying away discrete bundles, or quanta, of energy from the nucleus. Alpha particles don’t quietly drift away from the nucleus of Plutonium-239; they are propelled away at high speed with an energy of more than 5 MeV — five million electron volts. While 5 MeV is a trifling amount of energy in the sphere of human endeavors, at the atomic level it is enormous. In 1919, Rutherford bombarded nitrogen atoms with a particles of lesser energy. The a particles slammed into the nitrogen nuclei, yielding oxygen nuclei — a different element — and a free proton:

gHe ( a particle ) + —-> XgO + Jh (proton)

E. Pollard & W. Davidson, Applied Nuclear Physics 5-6 (1942).

A nucleus may also expel energy through emission of a gamma ray (y) of a particular wavelength. Likelihood of gamma emission depends on the specific nuclides. Strontium-90 does not emit gamma rays during decay. Iodine-131 does. Cobalt-60 emits two gamma rays in the MeV range, and has been used as an important source of radiation in the treatment of cancer. The detailed properties and mechanics of radioactivity and nuclear transformations are as awe-inspiring as they are complex. Why it is, for example, that unstable heavy nuclei emit a particles poses a challenging theoretical question, the answer to which is beyond the scope of this inquiry. 28 Yet a specific understanding of the statistical behavior of radionuclides (e.g., concepts such as radionuclide “half-life”) and of the ways in which ionizing radiation interacts with other matter is crucial to adequate analysis of the causation and negligence issues raised in this action.

E. Statistical Nature of Radioactivity

Current theory holds that events at the atomic or sub-atomic level occur according to statistical probabilities rather than any strict determinism. 29 Radioactive decay in any given quantity of a radioactive element occurs at a constant rate, yet no one can tell at what time any particular atom will decay. We know only the probability that it will decay within a chosen time period, or viewed another way, that over a chosen period of time, x number of nuclei in our sample will decay into “daughter” nuclides. The most important expression of this statistical approach is found in the concept of half-life. The half-life of a radionuclide is the specific length of time during which half of the nuclei in any amount of the radionuclide will have decayed- For example, if you start with a one gram sample of radium-226 (226Ra), after 1,600 years only half of the sample (0.5 gm) remains 226Ra. The other half has undergone radioactive decay:

ppR ppp 4 88 Ra---> 86 Rn + 2 He + Q (energy)

After another 1,600 years, only half of that remainder is still 226Ra (0.25 gm). Passage of 1,600 more years witnesses decay of one-half of that fraction, leaving Vs gram (0.125 gm) of 226Ra. The process of decay continues at this rate until no more 226Ra remains. To say, therefore, that a radionuclide such as strontium-90 has a half-life of 28.1 years means that half of the quantity existing at the beginning of the 28.1 years remains Sr at the end of that time.

*273 Half-life varies dramatically from radionuclide to radionuclide. Some isotopes last for half-lives of only a few seconds; others last far longer. Uranium (¶3 U), although radioactive, has a half-life of 4.51 X 109 years — nearly the age of the earth itself. See R. Heath, “Table of the Isotopes,” in Handbook of Chemistry and Physics B-232 to B-316 (64th ed. Weast 1983). 30 Half-life is indicative not only of the persistence of a radionuclide in the laboratory or the environment, but also of the intensity of its radioactive decay. Radiation yielded by one gram of iodine-136, an isotope found in the fireball of a nuclear explosion, is intense: emitting ¡3 particles and y rays in the MeV range, 136I decays rapidly, reflecting a half-life of 83 seconds.

53 I----> 54 Xe (stable) + p - + y + Q (energy)

Consequently its radioactivity fades rapidly. After 15 minutes, less than V2000 of the original amount is identifiable as 136I. After an hour more, the fraction remaining is nearly 2.28 x 10~15 of the original amount. In contrast, Plutonium-239, a radionuclide present in every nuclear fallout cloud to date, 31 persists with a half-life of 24,400 years. Consequently, all but a fraction of the estimated 3 tons of 239Pu deposited on the earth by fallout can still be found somewhere. See “Sources and Effects of Ionizing Radiation”, Report of the United Nations Scientific Committee on the Effects of Atomic Radiation (1977), PX-706/DX-605 [hereinafter cited as the UNSCEAR Report (1977) ], at 148.

Half-life is not an average lifetime for a radionuclide; 32 it is an expression of rate, of the statistical probability of decay over a specific time period.

The half-life of a radionuclide gives some immediate insight into its behavior and the nature of the hazard that might be associated with it. A small quantity of radionuclide with a half-life in the order of minutes will not persist long enough to present a significant hazard a few days later and it is not likely to become dispersed very far by natural forces. In contrast, a radionuclide with a half-life on the order of several years may represent a long-term hazard and become widely dispersed if not held in containment....

*274 1 F. Whicker & V. Schultz, Radioecology: Nuclear Energy and the Environment 44 (1982). The quantity of radioactive material that persists in relation to the number of half-lives is illustrated in Fig. 3.

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. Fig. 3. Relationship of time, expressed as number of half-lives, to the ■quantity of a ¡radioactive substance.

Quantity of radioactive material may be expressed in either of two ways: (1) the mass of the material; or (2) its radioactivity. To say, however, that a sample of Strontium-90 has a mass of x grams does not by itself offer any perspective on the amount of ionizing radiation being emitted by the sample at any given moment. The activity of a known mass of radioactive material may be computed as follows:

A* = 0.693 m N A Ty2 A Fj.

Where A* is the activity of the sample; m is the mass of the sample;

A is the atomic weight of the radionuclide;

T'/2 is the half-life in years (or whatever);

Ft is the conversion factor from years (or whatever) to a desired time period, e.g. minutes; seconds, etc.

NA is a constant, known as Avogadro’s number, expressing the number of atoms *275 in a mole (a mass in grams equal to the nuclide’s atomic weight) of material. See 1 F. Whicker & V. Schultz, Radioecology: Nuclear Energy and the Environment, supra at 45. For example, a 1.2 gram sample of sodium-24, an important radioactive by-product of nuclear weapons testing having a half-life of 15.0 hours, would have an initial activity of

A* = (0.693) (1.2 grams) (6.022 x 10^3 atoms/mole) (15.0 hours) (24 grams/mole) (3600 seconds/hr.) = 3.864 x 10” disintegrations per second.

This activity represents a rate of emission paralleling that of a sample of pure radium-226 having a mass of 1.0557 x 107 grams, or 10.5 metric tons. Of course, 24Na activity would fade quickly in comparison to the 226Ra; the mean life of 24Na atoms would be 21.64 hours, while atoms in our 10.5 metric tons would persist for a mean life of 2,308.8 years, making it a far more serious hazard overall.