Paper 2 Nuclear Physics Answers

Q1 Nuclear Decay Equation

1. ${}_{83}^{214}\mathrm{Bi}\to {}_{84}^{214}\mathrm{Po}+{}_{-1}^0\mathrm{e}$. Award one mark for the daughter nuclide and one for the emitted beta-minus particle. [2]
2. A neutron changes into a proton and a beta-minus particle is emitted. [2]
3. Continuous beta energies and conservation of energy/momentum require another neutral particle to carry missing energy and momentum. [2]

Q2 Half-life and Background

1. $620-40=580\mathrm{counts}\mathrm{mi}{\mathrm{n}}^{-1}$. [1]
2. $112.5-40=72.5\mathrm{counts}\mathrm{mi}{\mathrm{n}}^{-1}$. [1]
3. $580\to 290\to 145\to 72.5$, so 3 half-lives occur in $18\min$; $T_{1/2}=6.0\min$. [3]

Q3 Binding Energy

1. $E=\Delta m{c}^2=(3.20\times 10^{-28})(3.00\times 10^8{)}^2=2.88\times 10^{-11}\mathrm{J}$. [2]
2. It allows nuclei of different sizes to be compared for average stability/tightness of binding. [2]
3. Heavy nuclei split into medium-mass products with higher binding energy per nucleon, so total binding energy increases and energy is released. [2]