measures the speed at which radioactive material decays.
Half-life measures how long exactly half of a material
takes to decay. If the radioactive half-life of substance
X is 2 days, after two days, only 1/2 of the original
amount will be left. After another 2 days, only 1/2
of that half will remain, or 1/4 of the original amount,
and so on until the material has completely decayed.
In prostate cancer treatments using LDR brachytherapy,
seeds containing radioactive material are planted into
the prostate gland. Doctors determine what radioactive
material to put into the titanium shell. The radioactive
material will determine how strongly the gland will
be irradiated and for how long.