When the atoms of radioactive elements disintegrate, they form new elements with the emission of alpha and beta particles. The rate at which atoms disintegrate depends on how much radioactive element is present. As less and less radioactive isotope is left, the disintegration becomes slower and slower, but it ia never complete. The total life of a radioactive element is infinite, so the rate of radioactive decay of an element is described by its half-life.

Half-Life is a measured value for the amount of time it takes for a substance to decay to half of its original value. It can also be abbreviated by t1⁄2. It happens when a radioactive isotope goes through decay, which constantly halves the value in order to make it more stable. To better understand let's take an example. Half-life of radium is 1600 years which means that a given sample of radium will disintegrate half in 1600 years. If we start with 1 gram of radium now, then 0.5 gram of it will have disintegrated in 1600 years. After 1600 years, half of what will be left will disintegrate to half and so on.

Different radioactive elements have different half-life periods.

Element Radioisotope Half-life

Polonium Po-214 1.5 × 10-4 seconds
Iodine I-131 8 days
Phosphorus P-32 14.3 days
Iron Fe-59 44.3 days
Cobalt Co-60 5.3 years
Radium Ra-220 1.59 × 10³ years
Carbon C-14 5.8 × 10³ years
Uranium U-238 4.5 × 109 years