(a)[1]
What is the definition of the half-life of a radioactive isotope?
(b)
Radioactive isotope X decays into isotope Y. At time $t = 0$, the sample contains only nuclei of X. Fig. 9.1 shows how the numbers of X nuclei and Y nuclei change with $t$ as the sample decays.
(b(i))[1]
State the name of the quantity shown by the magnitude of the gradient of line X in Fig. 9.1.
(b(ii))[3]
State three conclusions about X or Y that may be drawn from Fig. 9.1.
(c)[3]
In part (b), the mass of radioactive isotope X in the sample is $7.3 \times 10^{-4}\,\text{kg}$ at time $t = 0$. Find the nucleon number of isotope X.