Neutron Effects on Living Things

also negotiating an agreement with the Commission International Confederation of Free Trade for Technical Co-operation in Africa. Unions International Co-operative Alliance In addition the Agency has granted consultative International Council of Scientific Unions status to nineteen non-governmental organizations, International Federation of Christian Trade and is considering applications from a number of Unions others. The nineteen are as follows: International Federation of Documentation International Federation of Industrial European Atomic Forum Producers of Electricity for Own European Confederation of Agriculture Consumption International Air Transport Association International Organization for Standardization International Cargo Handling Co-ordination International Union of Inland Navigation Association International Union of Producers and International Chamber of Commerce Distributors of Electrical Energy International Commission on Radiological Japan Industrial Forum Protection World Federation of United Nations International Committee on Radiological Associations Units and Measurements World Power Conference NEUTRON EFFECTS ON LIVING THINGS Scientific interest in neutrons and protons - two Although much has been learned about X-ray fundamental particles of the atomic nucleus - has and gamma-ray effects, comparatively little is known grown in recent years as the technology of peaceful about the biological effects of neutrons, and therefore uses of atomic energy has progressed. Such interest many of the Symposium papers reviewed the various also has increased because both protons and neutrons aspects of neutron experimentation. Similarly, since are encountered in outer space. However, only recently there is increasing interest in the biological effects has a thorough study of the biological effects of neutrons of protons, papers were given on that related subject. and protons become possible, as a result of progress in making physical measurements of the radiation dose Measurement Problems absorbed in biological systems (of plants and animals, The principal topic discussed at the Symposium for example). Reports of work in that field were pre was methodology for comparing absorption in tissue sented in December 1962, when IAEA sponsored at of different types of radiation. There seemed to be Harwell Laboratory in the United Kingdom the first general agreement among the participants that the international symposium on detection dosimetry (meas approach most commonly used in recent years, namely urement) and standardization of neutron radiation Relative Biological Effectiveness (RBE), can hardly sources. be considered adequate by itself as a method. The term RBE has been defined as the ratio of a "standard" The Harwell meeting was followed in October dose of X-radiation to the dose of test radiation re 1963 at Brookhaven National Laboratory, Long Island, quired to produce an equivalent biological effect. The New York, by the first scientific meeting sponsored standard dose is the amount of energy absorbed by a by IAEA in the U. S. Entitled "Biological Effects of given volume of plant or animal cells from the incoming Neutron Irradiations", the Symposium continued the X-rays. The test dose is the amount of energy ab review of problems of measuring radiation absorp sorbed from incoming neutrons. For example, if a tion in living things and provided in addition for several test dose of one rad* of neutrons produces the same reports dealing with the effects of radiation on living biological effect on the cells in question'as a standard organisms - plant, animal and human - and with dose of three rads of X-rays, the RBE of the neutrons delayed consequences of exposure to radiation, such is three. as: change in life span; tumour incidence; and fer * rad: unit of the amount of energy absorbed by material tility. Eighteen countries were represented. exposed to radiation. 26 refers to the pattern of distribution of energy as it is absorbed in a given material, such as animal cells. The term originates from pioneer work by physicists who study the lines or tracks left by nuclear particles as they penetrate photographic emulsions. When the film is developed, these tracks identify incoming particles which interact with the atoms of which the emulsion is composed. Nuclear particles which pene trate the cell itself produce secondary particles, which actually travel not just in a linear pattern, but three- dimensionally, penetrating various parts of the cell. The interplay of incoming nuclear particles (neutrons or protons) with particles which make up the cell prompts measurements by biologists assisted by physi cists. Resultant data are intended to help determine how radiation affects the life process in living cells. Similarly, data are collected on related experiments on tissue or organs or, to a more limited extent, on Column used for biology experiments on top of nuclear biological systems such as the nervous system, the reactor at Brookhaven. A container of plant seeds is endocrine system, etc. pushed into an elevator with o long rod. It is then lowered to the bottom of the column, halfway through the five-foot concrete shield which surrounds the LET was cricitized as being a "unidimensional" reactor. Some slow neutrons penetrate part way up the concept. Dr. H. H. Rossi, Department of Radiology, shield; a slab of bismuth filters out gamma rays. Columbia University, for example, has argued that 1. Seed container; 2. elevator; 3. neutron exposure investigators can indeed identify a cell track left by cavity; 4. bismuth slab; 5. shielding. (Photo. Brook- haven National Laboratory) an incoming nuclear particle, but it remains difficult to interpret the inconsistencies in data resulting, in RBE values for neutron exposure were stated part at least, from numerous variations found in dif ferent cells of the same basic type. Actually, because in many of the scientific papers presented at the of difficulties in "mapping" the trails left in the com Symposium. These values were also discussed at plex transfer of energy, measurements generally are length in a panel on biophysical considerations in neu made in gases stored in metal spheres of different tron experimentation. J. S. Krebs and R. W. Brauer, sizes. The gas-filled spheres serve as scale models of the U. S. Naval Radiological Defense Laboratory, of corresponding volumes of tissue. The density of a San Francisco, described recovery by cells in mice gas is generally of the order of some 1/1000th that of full reproductive function after exposure to neu of animal and human tissue. Thus most LET data trons at short-spaced intervals; the investigators are based on a multiplication of measurements actually noted that recovery after X-ray exposure is incom made in gases, rather than in living human or animal plete. They reported that destroyed cells are re cells, in which technological control is difficult. Some placed by division of the remaining cells when irra of the participants pointed out that there is only diations are spaced over long intervals of time. They limited scientific value in measurements of the amount conclude that knowledge of rate of recovery from large of radiation necessary to kill a single living cell. doses of neutron irradiation is more difficult to come Emphasis was placed on the importance of mounting by than for any other form of radiation, yet seems experiments in which new data can be collected on the essential if differences between effects caused by neu effects of radiation on the various life processes which trons and X-rays are to be interpreted significantly. take place in the cell. J. C. Moskalev, of the Institute They conclude: of Biophysics of the Academy of Medical Science in Moscow, advocated even more extensive investiga "The discoveries in the past few years about tion of organs and biological systems. He expressed the kinetics of accumulation of radiation injury the view that the functioning of cells together in the by cultured mammalian cells have made possi performance of a biological function is more signifi ble a more unified view of the process of injury cant to man's understanding of radiation effects than accumulation in whole mammals, with the re is the functioning of a cell as a single entity. conciling of many once divergent experimental viewpoints. With this new unity of view there is now the prospect of increasingly better under Measuring LET standing of the process of accumulation and re The use of "phantoms" or material containing pair of radiation injury in mammals. " chemical elements identical with those found in human beings, mice, dogs and guinea pigs was described by Interplay of Particles S. Snyder of Oak Ridge as part of a study of LET dis Another methodological concept discussed at tribution of neutron dose. When the cylindrical "phan length was linear energy transfer (LET). This term toms" are exposed to neutrons, the latter displace 27 nuclei of atoms in the cylinder, or interact with these on the basic mechanisms by which neutrons and pro nuclei to produce secondary neutrons and protons. tons produce effects in living things, there was also The LET of these recoil and secondary particles was occasional mention of the potential value of such work analysed by means of a computer for neutrons of dif in connection with maintaining health and safety pro fering energies, and types of "phantoms" compared. cedures in laboratories and other installations where V. I. Ivanov of the USSR Institute of Engineers these two fundamental nuclear particles are produced. and Physical Science, Moscow, presented evidence For example, protons are accelerated by cyclotrons of the utility of a new universal radiation dose unit in and other types of high energy particle accelerators standardizing measurements taken in various coun in dozens of universities and research organizations tries, and reported on work by investigators at the in various parts of the world. Neutrons are used in Joint Institute of Nuclear Research at Dubna in using experiments in connection with over 400 nuclear reac a synchrotron to produce a proton beam suitable for tors now in operation.

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