Sec 4 Physics Radioactivity topical questions

State what is meant by the random nature of radioactive decay.

Name the radiation described in each case: (a) a helium nucleus; (b) an electron emitted from a nucleus; (c) an electromagnetic wave from a nucleus.

State what the numbers A and Z mean in the nuclide symbol A/Z X.

Give two natural sources of background radiation.

Define the half-life of a radioactive isotope.

A nucleus of radon-222 (A = 222, Z = 86) emits an alpha particle.

1. (a)State the nucleon number and proton number of an alpha particle.[2]
2. (b)Determine the A and Z of the daughter nucleus and identify the element if Z = 84 is polonium.[2]
3. (c)Write the balanced nuclear equation for this decay.[1]

Compare alpha, beta and gamma radiations in terms of (a) their penetration and (b) their ionising power, stating one practical consequence of each ranking.

1. (a)Penetration ranking with the absorber that stops or reduces each.[3]
2. (b)Ionising ranking and why it runs opposite to penetration.[3]

The count rate from a source, corrected for background, is plotted against time. The corrected rate falls from 800 counts per minute to 400 counts per minute in 12 hours.

1. (a)State the half-life and justify it from the data.[2]
2. (b)Calculate the corrected count rate after a further 24 hours.[2]
3. (c)State why the corrected, not the raw, rate was plotted.[1]

A hospital uses a gamma-emitting tracer with a half-life of 6.0 hours. Immediately after injection, the activity in the patient corresponds to 2.4 × 10⁷ decays per second.

1. (a)Calculate the activity after 18 hours, assuming no biological removal.[2]
2. (b)Explain why a short half-life is chosen for the tracer.[2]
3. (c)State why gamma, rather than alpha, is essential here.[1]

A detector near a newly obtained source reads 4600 counts per minute; the source is removed and the detector reads 600 counts per minute. The isotope’s half-life is 8.0 hours.

1. (a)Calculate the corrected count rate of the source.[1]
2. (b)Calculate the corrected count rate after 24 hours.[2]
3. (c)Calculate the total reading on the meter after 24 hours.[2]
4. (d)Explain why the meter reading will never fall all the way to zero.[3]

An engineer must choose a radioactive isotope for two jobs: (1) a thin metal-foil thickness gauge; (2) a long-life power source for a remote lighthouse beacon. Only beta and gamma sources are available.

1. (a)Choose the radiation for the thickness gauge and explain the choice.[3]
2. (b)Choose the radiation and the half-life for the lighthouse source and explain both.[4]

A museum uses carbon dating on a wooden artefact. Living wood has a corrected carbon-14 count rate of 16.0 counts per minute per gram; the artefact gives 2.00 counts per minute per gram. The half-life of carbon-14 is 5700 years.

1. (a)Determine how many half-lives have elapsed since the wood was alive.[2]
2. (b)Calculate the age of the artefact.[2]
3. (c)State one assumption the dating method makes.[2]
4. (d)The measured rate is corrected for background before use. Explain why this matters more for old samples than fresh ones.[2]

A school holds three sealed sources: P (alpha), Q (beta), R (gamma), each with a half-life of many years. During a safety audit, a student argues: "Source P is the most dangerous, so it should never be taken out of the store." The teacher disagrees with the word "never".

1. (a)Explain why P is the strongest ioniser but is not automatically the most dangerous in every situation.[3]
2. (b)Describe the conditions under which source P becomes extremely dangerous.[2]
3. (c)State the safety precautions for handling P in a lesson and justify each one.[3]