Some isotopes of phosphorus are radioactive.

The isotope phosphorus-32 (${}_{15}^{32}P$) has the symbol:

${}_{15}^{32}P$

The isotope phosphorus-30 (${}_{15}^{30}P$) has the symbol:

${}_{15}^{30}P$

State the number of protons in a nucleus of phosphorus-32.

Give one similarity and one difference between the nucleus of phosphorus-30 and the nucleus of phosphorus-32.

A physicist measures the radiation emitted by a sample of phosphorus-32.

The physicist's results are shown in Table 18.1.

Explain why the physicist's three measurements are not the same.

Use the physicist's results in Table 18.1 to calculate the mean count-rate for phosphorus-32.

Phosphorus-32 emits beta radiation. The physicist puts a 5 mm thick sheet of aluminium between the phosphorus-32 sample and the detector. State what happens to the count-rate.

Explain what is meant by the half-life of a radioactive isotope.

The half-life of phosphorus-32 is 14 days. The count-rate of a sample of phosphorus-32 is 1200 counts per second. Calculate the count-rate of the phosphorus-32 after 56 days.

A radioactive isotope can be used as a tracer in a patient's body. It is monitored by a radiation detector outside the body.

Four possible radioactive isotopes are shown in Table 18.2.

Radiographers wear a lead apron when they work with radioactive isotopes. Explain why.

Which radioactive isotope from Table 18.2 is best to use as a radioactive tracer in a patient's body? Explain your answer.