When we are looking at nuclear transformation we consider both nuclear decay and nuclear reactions.
Nuclear decay is when an unstable istope split into smaller components.. There are several types of nuclear, namely alpha, beta, gamma and positron. The type of decay can be predicted by looking at the Nuclear/Proton ratio (N/Z from here and on):
1. When an atom has too many
protons (thus a small N/Z), it preferrs to reduce the number of
protons to increase the N/Z value. This can be achieved by positron emission or electron capture where protons are transformed into neutrons.
2. If an atom has too many
neutrons (thus a high N/Z) it would undergo beta decay in which a
neutrons are transformed into a proton + an electron and this decreases the N/Z value.
3. If an atom has too many of both
protons and
neutrons then it is most likely to undergo alpha decay, where alpha particles (Helium atoms) are ejected from the nucleus.
Reference: Silberberg CHEMISTRY 3rd edition
So why do nuclear decays occur? There is an adhesive force called
strong force within nucleii which holds neutrons and protons together. At the same time there is also a repulsive force between those atomic particles. In order to become a stable nucleus, an atom must undergo a decay to adjust the imbalance.
Earlier I have mentioend that nuclear transformation includes also nuclear reactions. Besides the spliting of radioisotopes into smaller components, we also consider the case when smaller components join to form "heavier" atoms. This scenario is very common in nuclear reactors where various elements are bombarded by neutrons. (Also happens in nuclear accelerator)
There are naturally occuring radioisotopes as well as artificial radioisotopes. Nuclear decay is a naturally occuring process where as
producing the radioisotops is not necessarily natural (as suggest by the two examples above). So you could use these information to answer the question you have posted
Hope that helps
