Discrimination in radiation detection circuits refers to the process of distinguishing between different types of radiation on the basis of pulse height. A discriminator circuit selects the minimum or maximum pulse height that is to be counted. For example a discriminator circuit is used in the neutron detector to distinguish the large pulses from alpha ionisation (neutron absorption in the detector produces alpha particles) from the much smaller ones that would be caused by gamma rays.
Special Reference: U.S. Department of Energy, Instrumantation and Control. DOE Fundamentals Handbook, Volume 2 of 2. June 1992.