(Radioactive decay – qualitative)
A sealed source of radioisotope Z is kept in the school laboratory. The half-life of Z is 2 h.
(i) Define the half-life of a radioactive substance.
(ii) Explain qualitatively why, even after a large number of half-life intervals, the number of undecayed nuclei of Z in the source never actually becomes zero.
(iii) Without performing any numerical calculations, describe how the activity of the source will change after 2 h, 4 h and 6 h, stating the reason for your answer in each case.