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Unformatted text preview: What you should know about ... Nuclear Physics 1. Nuclei and strong interaction [Q12,Q13] nuclear notation: Z protons and A total nucleons = A Z X ; size: r = r A 1 / 3 , with r 1 . 2fm Strong interaction between color neutral objects (such as nucleons) is short range ( < 2fm) Binding energy: E b = ( parts E parts )- E sys Mass defect: m = ( parts m parts )- m sys = E b /c 2 = Zm H + Nm n- m atom binding energy formula ( A > 20): E b ( A,Z ) = a I A- a S A 2 / 3- a C Z 2 /A 1 / 3- a A ( A- 2 Z ) 2 /A with a I = 15 . 56MeV, a S = 17 . 23MeV, a C = 0 . 697MeV, a A = 23 . 285MeV binding energy per nucleon, e b = E b /A and binding energy vs. mass ( E = mc 2 ) 2. Radioactive decay (beta, alpha, gamma) [Q13,Q14] Predicting stability and type of decay: energy level diagrams, binding energy formula, atomic mass beta: - = n- p + + e- + e + = p +- n + e + + e EC = p + + e-- n + e alpha: helium nuclei (2 protons, 2 neutrons) gamma: photons from decays of excited nuclear states activity - dN/dt = N = solution: N ( t ) = N e- t = half-life t 1 / 2 = ln2 / Z stable ( A ) for stability against decay: Z stable = A 1 . 0084 2+0 . 015 A 2 / 3 . This formula gives the stable isotope for even-odd nuclei ( A is odd) or even-even nuclei (both Z stable and N are even). For odd-odd nuclei ( A even, N,Z stable odd) the neighboring even-even nuclei may have lower atomic mass, in which case the stable nuclei have Z = Z stable 1....
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