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FORM SEVEN PHYSICS (P 3.5 -ATOMIC/NUCLEAR) ANSWERS WORKSHEET THREE: NUCLEAR PHYSICS 1. 28 protons and 32 neutrons. 2. Isotopes are atoms of the same element with different numbers of neutrons. 3. Fusion is a nuclear reaction in which two smaller nuclei join together to form a larger nucleus. 4. Fission is a nuclear reaction in which a large nuclei splits into smaller ones. 5. For a chain reaction to occur, the nucleus needs to release 3 or more neutrons per decay event. The decay needs to be initiated by collision with a neutron and there needs to be more than the critical mass of material present. 6 (a) 241 95 7. (a) 14 6 8. (a) Gamma 9. (a) Mass alpha particle = 6.64591 x 10-27 Am C 237 93 Np + 14 7 4 2 He N + (b) Beta Total mass of nucleons 0 1 e (c) Ra 222 86 Cu 0 1 (b) 226 88 (b) 60 29 Gamma (d) e Rn + + 60 28 4 2 He Ni Alpha = 2( 1.67338 x 10-27) + 2(1.67483 x 10-27) = 3.3467 x 10-27 + 3.34966 x 10-27 = 6.69624 x 10-27 (b) 10. Mass deficit = 0.05051 x 10-27 Binding energy = 0.05051 x 10-27 x (3 x 108)2 = 4.5459 x 10-12 J Binding energy per nucleon = 1.136475 x 10-12 J Rest mass of products = 6.6443 x 10-27 + 1.6747 x 10-27 = 8.3190 x 10-27 kg Rest mass of reactants = 3.3434 x 10-27 + 5.0 x 10-27 = 8.3434 x 10-27 kg Mass deficit = 2.44 x 10-29 kg Binding energy = energy released = 2.44 x 10-29 x (3 x 108)2 = 2.196 x 10-12 J 11. (a) Mass of 1 amu = 1.6604 x 10-27 kg (b) Energy equivalent = mc2 = 1.6604 x 10-27 x (3 x 108)2 = 1.49436 x 10 –10 J (c) In eV = 9.340 x 108 eV = 934 MeV 12. Binding energy per nucleon Fe He U H Mass Number (a) Iron. Iron has the highest binding energy per nucleon and so the iron nucleus needs more energy input per nucleon than any other nucleus to separate into its individual nucleons. (b) Elements to the right of iron become progressively less stable in their larger nuclei and so by splitting (fission) their nuclei can become smaller and more stable and release energy in doing so. Elements to the left of iron have less stable small nuclei and so by joining two smaller nuclei together (fusion) to form a larger nuclei there can be an increase in stability and a release of energy.