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Unformatted text preview: CHAPTER 32 IONIZING RADIATION, NUCLEAR ENERGY, AND ELEMENTARY PARTICLES ANSWERS TO FOCUS ON CONCEPTS QUESTIONS 1. (c) The biologically equivalent dose (in rems) is the absorbed dose (in rads) times the relative biological effectiveness. (See Equation 32.4.) 2. (d) Equation 32.3 defines the relative biological effectiveness as the dose of 200-keV X-rays that produces a certain biological effect divided by the dose of radiation that produces the same biological effect. Thus, since RBE A = 2 RBE B , it takes a smaller dose of A to produce the same biological effect as B, smaller by a factor of 2. 3. 9.0 10 3 rem 4. (b) Since electric charge must be conserved, we know that the number of protons must be the same before and after the reaction takes place. Therefore, Z + 7 = 6 + 1, so Z = 0. We also know that the total number of nucleons must be conserved, so the total number before and after the reaction takes place must be the same. Therefore, A + 14 = 14 + 1, so A = 1. With a single uncharged nucleon in the nucleus, the unknown species must be a neutron 1 n . 5. (a) The symbol for the particle is 4 2 He , and the symbol for the proton p is 1 1 H . Therefore, there are 2 + 13 = 15 protons present before the reaction takes place and 15 + 1 = 16 protons present after the reaction takes place, which violates the conservation of electric charge. There are 27 + 4 = 31 nucleons present before the reaction takes place and 1 + 31 = 32 nucleons present after the reaction takes place, which violates the conservation of nucleon number. 6. (e) The compound nucleus is 236 92 U for any X and Y. Since the total number of nucleons is conserved, it follows that 1 + 235 = A X + A Y + , where is the number of neutrons 1 n produced by the reaction. Therefore, greater values of lead to smaller values for A X and A Y . Since electric charge also is conserved, it follows that 0 + 92 = Z X + Z Y + (0). Therefore, Z X + Z Y = 92 for any X and Y. 89 IONIZING RADIATION, NUCLEAR ENERGY, AND ELEMENTARY PARTICLES 7. (b) In a fission reactor each fission event, on average, must produce at least one neutron. Otherwise there would be no neutrons to cause additional fission events, and it would not be possible to establish a controlled chain reaction. If the fission products of the reaction each have a binding energy per nucleon that is less than the binding energy per nucleon of the starting nucleus, the reaction does not produce energy. It only produces energy when the fission products have, on average, a binding energy per nucleon that is greater than the binding energy per nucleon of the starting nucleus. 8. (a) In order for a fusion reaction to be potentially energy-producing, the binding energy per nucleon of the starting nuclei must be smaller than the binding energy per nucleon of the product nucleus. Since the maximum binding energy per nucleon occurs at a nucleon number of about 60, the starting nuclei with nucleon numbers of 30 in reaction I have the...
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