[3](a)A radioactive source has an initial activity of 800 counts per minute. Its half-life is 5.3 years. Calculate the activity after 15.9 years.

[2](a)A Geiger-Muller tube records 68 counts per minute near a source, and 12 counts per minute with the source removed. Calculate the corrected count rate due to the source alone.

[2](b)Explain why this background correction is necessary.

[3](a)Radium-226 (atomic number 88) decays by alpha emission to form radon. Write a balanced nuclear equation for this decay, including mass and atomic numbers.

[3](a)Compare the penetrating power of alpha, beta and gamma radiation, stating what is needed to stop each.

[2](a)A radioactive sample starts with an activity of 1000 counts/minute. After 3 half-lives, calculate its activity.

[2](a)A sample's activity falls from 500 to 62.5 counts/minute. Calculate how many half-lives have passed.

[2](a)A detector records 45 counts per minute near a source and 5 counts per minute with no source present. Calculate the corrected count rate.

[3](a)Carbon-14 (atomic number 6) decays by beta emission. Write a balanced nuclear equation for this decay, showing the resulting element (nitrogen, atomic number 7).

[2](a)State one medical and one industrial use of radioactive isotopes.

[2](a)Explain why alpha particles are more strongly ionising than gamma rays, despite being less penetrating.