The stability of a radioactive element can influence the rate of nuclear decay reaction. Pressure, temperature and concentration only affects chemical changes. These factors would not have any effect on radioactive decay of an element.
Every atomic nucleus have a specific neutron/proton ratio which ensures the stability of the nucleus.
Any nucleus that deviates from the stability ratio will continue to split until it achieves stability.
The more unstable a nucleus is, the faster it decays.
This is the basis of radioactive decay of elements.
Due to the fact that the crystals can no longer dissolve and adding more solute to the same temperature will continue not to dissolve the crystals making it more and more saturated leading to supersaturated solution
