(a)[1]
Work out how many neutrons are present in a nucleus of iodine-131.
(b)[1]
Explain what is meant by ionising radiations.
(c)[3]
Use the data in Fig. 8.1 to determine the half-life of iodine-131. Show clearly how you used the graph.
(d)[2]
Calculate the time taken for it to decay to 25% of its starting amount.