What is half of an hour of an hour?

Answer 1

A half-life of one hour means that, in one hour, one half of an unstable nuclear substance, a quantity of some radionuclide, will decay. Since half-life is logarithmic, after a second hour, half of the half will decay, leaving one quarter, and, after a third hour, half of the quarter will remain, leaving one eighth, and so on. The equation for half-life is ...

AT = A0 2(-T/H)

... where A0 is the starting activity, AT is the activity remaining after some time T, and H is half-life in units of T.

Note that many radionuclides, when they undergo a decay event, will transmute into some other radionuclide, which also has a half-life. A consequence of this is that many samples have several different decay "daughter" products, with different half-lives and different equilibrium states, so the technique of measuring the amount of material can often be complex. Also, some radionuclides have multiple decay schemes, each with a different probability and each with a different half-life, again, complicating things.

Usually, half-life is constant so, if you can measure the half-life, you can often identify the radionuclide. The exception to this is radionuclides that decay by beta+ decay, but they have insufficient excess energy in the nucleus to initiate that without electron capture, but they are also in an ionized state, having no electrons. In this case, it will appear that half-life is extended.