Activity is the rate of radioactive decay or the emission rate of a radiation from radioactive material. The cumulated activity is useful for nuclides that emit multiple radiations per disintegration.
The units for activity are the curie (Ci) and the becquerel (Bq).

The biological half-life is the time required for the concentration of a substance in a biological system to be reduced by one half. A biological half-life includes usual processes for eliminating substances without radioactive decay.

See also Biological Radioactive Half-Life.

Disintegration is a synonym for radioactive decay.

Time in which 50% of a radioactive substance through biological (physiological) processes and decay is removed.
The effective radioactive half-life is shorter or equal than the physical or the biological radioactive half-life alone.

Effective Radioactive Half-Life (t_eff) =
(Biological Radioactive Half-Life x Physical Radioactive Half-Life) /
(Biological Radioactive Half-Life + Physical Radioactive Half-Life)

See also Half-Life, Biological Half-Life, Physical Radioactive Half-Life.

An eluate is the solvent containing the decay product when a generator is eluted (gathering the daughter radionuclide from a generator using a suitable solvent).

See also Generator.