IEEE/ANSI N42.14-1999

The purpose of this standard is to provide a basis for the routine calibration and use of Ge semiconductor detectors for the measurement of gamma-ray emission rates and, thereeby, the activities of the radionuclides in a sample. It is intended for use by persons who have an understanding of the principles of Ge gamma-ray spectrometry and are responsible for the development of procedures for the calibration and use of such detectors. This standard is primarily intended for guidance on how to set up and use a system for routine analytical measurements. A typical gamma-ray spectrometer consists of a Ge detector with its liquid-nitrogen or mechanically refrigerated cryostat and preamplifier, detector bias supply, linear amplifier, analog-to-digital converter (ADC), multichannel storage of the spectrum, and data-readout devices. A radiation shield often surrounds the detector to reduce the counting rate from room-background radiation (see Annex E for shield construction guidelines). Photons (X and gamma rays) interact with the Ge crystal to produce electron-hole pairs. These electrons and holes are collected to produce a pulse whose amplitude is proportional to the energy deposited in the active volume of the Ge crystal. Each pulse is amplified, shaped, and sorted according to pulse height, using an ADC to produce a histogram showing, as a function of energy, the number of photons absorbed by the detector. After the accumulation of a sufficient number of pulses, the histogram displays a spectrum of one or more peaks with an approximately normal (Gaussian) distribution corresponding to photons that interacted with the detector.