mean life

noun, Physics.
1.
the average time that an unstable particle or nucleus survives before it decays.
Also called average life, lifetime.
British Dictionary definitions for mean life

mean life

noun
1.
(physics) the average time of existence of an unstable or reactive entity, such as a nucleus, elementary particle, charge carrier, etc; lifetime. It is equal to the half-life divided by 0.693 15 τ