Paper 4 Nuclear Physics Drills

Q1 Half-life from Counting Data

A detector records counts for $60\mathrm{s}$ at each time. A separate background measurement gives $20\mathrm{counts}\mathrm{mi}{\mathrm{n}}^{-1}$.

$t$/min	0	4	8	12	16	20
measured count rate/$\mathrm{counts}\mathrm{mi}{\mathrm{n}}^{-1}$	661	470	342	244	181	132
corrected source count rate/$\mathrm{counts}\mathrm{mi}{\mathrm{n}}^{-1}$

1. Complete the corrected source-count-rate row. [2]

2. Plot corrected source count rate against $t$ and draw a smooth best-fit decay curve. [5]
3. Use the graph to determine the half-life. [2]
4. Calculate the decay constant in ${\mathrm{s}}^{-1}$. [2]
5. Explain why the percentage statistical uncertainty becomes larger at later times. [2]
6. State one improvement that reduces random counting uncertainty without changing the source. [1]

Q2 Nuclear Equation Checks

1. State the two conservation rules used to balance nuclear equations. [2]
2. Explain why chemical charge balance is not the same as nuclear charge conservation. [2]
3. State one reason repeated readings are needed in radiation counting. [1]