The example that causes the most confusion is the decay of the free neutron with a half-life of 10.3 minutes and an average lifetime of 14.9 minutes. Note that the radioactive half-life is not the same as the average lifetime, the half-life being 0.693 times the average lifetime. The relationship between these quantities is as follows.
The predictions of decay can be stated in terms of the half-life, the decay constant, or the average lifetime. The only thing which can alter the half-life is direct nuclear interaction with a particle from outside, e.g., a high energy collision in an accelerator. It is independent of the chemistry of the atomic surface, and independent of the ordinary physical factors of the outside world. The half-life is independent of the physical state (solid, liquid, gas), temperature, pressure, the chemical compound in which the nucleus finds itself, and essentially any other outside influence. The tiny nuclear size compared to the atom and the enormity of the forces which act within it make it almost totally impervious to the outside world.
The radioactive half-life for a given radioisotope is a measure of the tendency of the nucleus to 'decay' or 'disintegrate' and as such is based purely upon that probability. Radioactive Half-Life Radioactive Half-Life
