noun
: the constant ratio of the number of radioactive atoms disintegrating in any specified short unit interval of time to the total number of atoms of the same kind still intact at the beginning of that interval
noun
: the constant ratio of the number of radioactive atoms disintegrating in any specified short unit interval of time to the total number of atoms of the same kind still intact at the beginning of that interval
Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012