IEEE/ANSI N42.12-1980

New IEEE Standard - Superseded.

Methods are established for performance testing, calibration, and use of sodium iodide detector systems for the measurement of gamma-ray emission rates of radionuclides, assay for radioactivity, and the determination of gamma-ray energies.

Both energy calibration and efficiency calibration are covered.

Three techniques are considered:

• total spectrum counting, which employs a system that counts all events above a low-energy threshold;
• single-channel analyzer counting, which employs a system with a counting window that establishes upper and lower energy boundaries; and
• multichannel analyzer counting, which employs a system utilizing multiple counting windows.

This standard establishes methods for performance testing, calibration, and usage of sodium iodide detector systems for the measurement of gamma-ray emission rates of radionuclides; the assay for radioactivity; and the determination of gamma-ray energies. It covers both energy calibration and efficiency calibration.

The following three techniques are considered:

• Total spectrum counting (see 5.1) employs a system that counts all events above a low-energy threshold (see 7.1, 7.2, and 7.3).
• Single-channel analyzer counting (see 5.2) employs a system with a counting window which establishes upper and lower energy boundaries (see 7.1, 7.2, and 7.3).
• Multichannel analyzer counting (see 5.3) employs a system in which multiple counting windows are utilized. This technique applies to measurements that do not involve overlapping peaks and those for which the continuum under the full-energy peak can be subtracted without introducing unacceptable error [4].

The purpose of this document is to provide a standardized basis for the calibration and usage of sodium iodide detector systems for the measurement of gamma-ray emission rates of radionuclides.

Typical applications include radionuclide identification and assay in various industrial, environmental, and medical applications.

A sodium iodide detector system consists of: three major components: a scintillating medium that produces a flash of light when ionizing radiation interacts with it; one or more photomultipliers, optically coupled to the scintillator, which converts the light flash to an amplified electrical impulse; and associated electronic instrumentation which powers the photomultiplier and processes the output signal. [See ANSI/IEEE Std 398-1972 (Reaff 1977), Test Procedures for Photomultipliers for Scintillation Counting and Glossary for Scintillation Counting Field.]

The theory of operation of sodium iodide detectors is presented in numerous publications, including refs [1] - [3].