This standard establishes methods for performance testing, calibration, and usage of thallium-activated sodium iodide [NaI(Tl)] detector systems for the measurement of gamma ray emission rates of radionuclides; the assay for radioactivity; and the determination of gamma ray energies and intensities. It covers both energy calibration and efficiency calibration. The following three techniques are considered: a) Total spectrum counting (see 4.1) employs a system that counts all pulses above a low-energy threshold (see 6.1, 6.2, and 6.3). b) Single-channel analyzer (SCA) counting (see 4.2) employs a system with a counting "window," which establishes upper and lower energy boundaries (see 6.1, 6.2, and 6.3). c) Multichannel analyzer (MCA) counting (see 4.3) employs a system in which multiple counting windows are utilized. This technique allows measurements for which the continuum under the full energy peak may be subtracted without introducing unacceptable error. In case of overlapping peaks in the spectrum, it is realized that an MCA with access to a spectrum-stripping program is necessary. Such cases are not covered by this standard.