Chapter 4 Monitoring Accidental Radiation Releases Eachtest is conducted under conditions in which remedial actions could be effective should an accidental release of radioactive material occur. quantity of radiation required to produce one coulomb of electrical charge in one kilogram ofdry air. A rem is the dose in tissue resulting from the absorption of a rad of radiation multiplied by a “*quality factor’’ that depends on the type of INTRODUCTION Although nuclear tests are designed to minimize the chance that radioactive material could be re-leased to the atmosphere, it is assumed as a precaution for each test that an accident may occur. To reduce the impact of a possible accident, tests are conducted only under circumstances whereby remedial actions could be taken if necessary. If it is estimated that the projected radioactive fallout from radiation. A rad is defined as 100 ergs (a small unit of energy) per gram of exposed tissue. Recently accepted international units of radiation are now the gray (Gy), equal to 100 rads, and the sievert (Sv), equal to 100 rems. a release would reach an area where remedial actions are not feasible, the test will be postponed. PRODUCTS OF A NUCLEAR EXPLOSION Responsibility for radiation safety measures for the nuclear testing program is divided between the Department of Energy (DOE) and the Environ- mental Protection Agency (EPA). The Department of Energy oversees monitoring within the bounda- A nuclear explosion creates two sources of radioactivity: the first sourceis the direct products of the nuclear reaction, and the secondis the radioactivity induced in the surrounding material by the explosion-generated neutrons. In a fission reaction, the splitting of a nucleus creates two or more new nuclei that are often intensely radioactive. The products occur predominantly in two major groups of elements as shown in figure 4-1. The neutrons produced by the reaction also react with external materials such as the device canister, surrounding rock, etc., making those materials radioactive as well. In addition to these generated radioactivities, unburned nuclear fission fuel (especially plutonium) is also a radioactive containment. The helium nuciei formed by fusion reactions are not radioactive.! However, neutrons produced in the fusion reaction sull will make outside material radioactive. Depending on the design of the explosive device and its percentage of fission and fusion, a wide range of radioactive material can be released with half lives ries of the Nevada Test Site (NTS). The Environ- mental Protection Agency monitors the population aroundthe test site and evaluates the contribution of nuclear testing to human radiation exposure through air, water, and food. WHATIS RADIATION? The nuclei of certain elements disintegrate spontaneously. They may emit particles, or electromag- netic waves (gammarays or x-rays), or both. These emissions constitute radiation. The isotopes are called radionuclides. They are said to be radioactive, and their property of emitting radiation is called radioactive decay. The rate of decay is characteristic of each particular radionuclide and provides a measure ofits radioactivity. The common unit of radioactivity was the curie (Ci), defined as 3.7 x 10!° decays per second, which of less than a second to more than billion years. is the radioactivity of one gram of radium. Recently, a new unit, the becquerel (Bq), has been adopted, defined as one decay per second. Exposure of biological tissue to radiation is measured in termsof rems (standing for roentgen equivalent man). A roentgen (R) is a unit of exposure equivalent to the The debris from nuclear detonations contain a large numberof radioactive isotopes, which emit predominantly gammaandbeta radiation. Someof the more common radionuclides involved in a nuclear explosion are listed in table 4-1. 'This, incidentally, is why commercial fusion reactors (if they could be created) would be a relatively clean source of energy. 2The half-life is the ume required for half of the atoms of a radioactive substance to undergo a nuclear transformation to a more stable element. -59-