An instrument used to indicate the number of occurrences of counter-output pulses falling within each of one or more specified amplitude (i.e., energy) ranges; used to obtain the energy spectrum of gamma [[radiation|radiations]]. It is possible to separate and count the pulses corresponding to one or more specific energy ranges which serve as an indicator of some specific radioactive isotope in the [[formation]]. See also [[spectral gamma ray log|spectral gamma-ray logging]], [[induced spectral gamma ray log|induced spectral gamma-ray logging]], and [[channel]].