Diana Preston - Before the Fallout

“this great physicist… we are”: S. Goudsmit’s letter to R. Peierls of 21 January 1977, Goudsmit papers, series 3, box 10, folder 97, AIP.

“An invention. make”: Transcript of F. Houtermans’s interview for the BBC TV program “The Building of the Bomb,” 1965.

“In the west… possibilities”; “The possibility was… do with it”: Transcript of R. Peierls’s interview for ibid.

“In the first place… arm’s length”: Transcript of O. Frischs’s interview for ibid.

“Though a brilliant theoretician… numbers”: New York Review of Books, 22 April 1993.

“changed everything… politics”: Quoted in Szasz, British Scientists and the Manhattan Project, p. 103.

“I’m afraid created”: Guardian, 2 August 1986.

“If you are… values”: Oppenheimer made these remarks in his farewell speech to the Association of Los Alamos Scientists on 2 November 1940, quoted in full in Kimball-Smith and Weiner, eds., Robert Oppenheimer — Letters and Recollections, pp. 31 c-25.

“easy for even wise men easy. about”: Quoted in Szasz, British Scientists and the Manhattan Project, p. 78.

“in science persons”: E. Curie, Madame Curie, p. 233.

“People are not important… people”: Author’s interview with Lorna Arnold 11 December 2001.

“When I was younger… individual”: Transcript of interview for BBC TV Horizon program “To Die, To Live,” 1975.

alpha particles (alpha rays).One of the three types of radiation (see also beta particlesand gamma particles)discovered around 1900. Alpha particles are helium nuclei made up of two protons and two neutrons. They are slow and heavy, compared with other forms of radiation, and cannot penetrate paper.

artificial radioactivity.Radioactivity induced by bombarding and thus destabilizing nuclei.

atom.The basic unit of matter, consisting of a single nucleus surrounded by orbiting electrons.

atomic number.The number of protons in the nucleus of an atom. The number of protons is equal to the number of electrons orbiting the nucleus, and since an atom’s chemical properties are determined by the number of such electrons, the atomic number establishes an atom’s chemical identity.

atomic weight.The mass of an atom, effectively equivalent to the number of its protons and neutrons. Hydrogen’s atomic weight is thus one.

beta particles (beta rays).Radiation in the form of electrons traveling at high speed. They are lighter and faster than alpha particles and more penetrating but can be stopped by a sheet of metal.

chain reaction.A self-sustaining nuclear reaction triggered when a neutron induces a nucleus to fission, thereby causing it to release energy and further neutrons, which, in turn, cause further fissions.

complementarity.The theory developed by Niels Bohr that seemingly conflicting or ambiguous findings may need to be placed side by side to create a full understanding of a phenomenon.

critical mass.The amount of fissile material needed to sustain a chain reaction.

deuterium.The isotope of hydrogen otherwise known as heavy hydrogen (see also heavy water).

electron.An elementary particle carrying one unit of negative electrical charge.

enriched uranium.Uranium with a higher content of the isotope U-235 than natural uranium.

fissile material.Any element containing an isotope with nuclei capable of undergoing fission. Uranium-235 and plutonium-239 are important fissile materials.

fission.The splitting of the nucleus of a heavy atom (i.e., belonging to an element with a high atomic number that is classified near the top end of the periodic table) accompanied by the release of energy and of atomic particles. It can occur spontaneously or be induced by external stimuli.

fusion.The combination of two light nuclei to form a single heavier nucleus accompanied by a release of energy.

gamma particles (gamma rays).The name originally given to the most penetrating of the three types of radiation discovered to be emitted from radioactive substances as they decay. Gamma rays consist of electromagnetic radiation, like light.

gaseous diffusion.A method for enriching uranium (i.e., increasing the content of U-235) by pumping uranium hexafluoride gas through permeable membranes.

graphite.An elemental form of carbon used as a moderator.

half-life.The time taken for a radioactive material, as it decays, to reach half its previous radioactivity. In two half-lives it would be at a quarter of its original level. Half-lives range from fractions of a second to billions of years.

heavy water.Water containing significantly more than the natural proportion (1 in 6,000) of heavy hydrogen (deuterium) atoms to ordinary hydrogen atoms. Hydrogen atoms have one proton. Deuterium atoms contain one proton and one neutron. Heavy water slows neutrons down more effectively and absorbs them less than ordinary water and is therefore suitable for use as a moderator.

ions and ionization.Ions are electrically charged atoms and molecules. Ionization—the production of ions—can occur in many ways and is associated with radioactivity because of the strong electrical disturbances caused when the products of radioactive decay pass through their surroundings.

isotopes.Different forms of the same element. Isotopes of the same element have the same number of protons in their nucleus, but the number of neutrons varies.

liquid drop model.The model of the atom developed by Niels Bohr, who visualized it as resembling a droplet of liquid with nuclear forces playing the part of surface tension.

moderator.A substance, such as heavy water or graphite, used in thermal reactors to slow neutrons down and thereby increase their chances of causing fission.

natural uranium.Uranium whose isotopic composition, as it occurs in nature, has not been altered.

neutron.An uncharged, that is, electrically neutral, particle found in the nucleus of every atom heavier than hydrogen. It has almost the same mass as a proton but is very slightly heavier.

nuclear energy.The energy released by a nuclear reaction such as fission.

nucleus.The positively charged central core of the atom. It carries over 99.9 percent of the atom’s mass but occupies only a tiny part of its volume. All nuclei consist of protons and neutrons, except for the nucleus of hydrogen, which contains only one proton.

periodic table.The table classifying elements according to their atomic number (see atomic number).The number derives from the number of protons in their nucleus. Thus hydrogen with its single proton is at number one in the table.

plutonium.An element with atomic number 94 formed in nuclear fission reactors.

positron.The antiparticle of the electron. It has the same mass but carries a positive charge.

proton.A positively charged particle found in the nucleus of every atom.

quantum mechanics.A mathematical system developed by Werner Heisenberg and others based on matrix algebra and used to describe the properties of matter at the atomic level.