This International Standard specifies methods of calibration and routine tests of scintillation detector systems for the measurement of gamma-ray energies and emission rates of radionuclides and the assay of radioactivity. This International Standard is applicable to scintillation detector systems based on inorganic scintillators for photon measurements. Typical applications include radionuclide identification and assay in various industrial, environmental, and medical applications. The detector system consists of three major components: a scintillating material that produces photons of light when ionizing radiation interacts with it; one or more photomultipliers or photodiodes, optically coupled to the scintillator, which convert the light photons to an amplified electrical pulse or pulses; and associated electronic instrumentation which powers the photomultiplier and processes the output signal. Both energy calibration and efficiency calibration are covered. The following three techniques are considered: a) total spectrum counting (see 3.1) which employs a system that counts all pulses above a low-energy threshold (see 5.1, 5.2 and 5.3); b) single-channel analyzer (SCA) counting (see 3.2) which employs a system with a counting channel established through upper and lower energy boundaries (see 5.1, 5.2, and 5.3); c) multichannel analyzer counting (see 3.3) which employs a system in which multiple counting windows are utilized. This technique allows measurements for which the continuum under the total absorption peak may be subtracted without introducing unacceptable error. In case of overlapping peaks in the spectrum, a multichannel analyzer (MCA) with access to a peak deconvolution program is necessary. This case is not covered by this standard.