Recommended standards for gamma-ray energy calibration

A consistent set of gamma-ray energies, generally with uncertainties of les s than 10 ppm, has been prepared for use in the energy calibration of gamma -ray spectra. The energy scale used for the previously recommended standard s (1979) has been modified to take into account subsequent adjustments in t he fundamental constants (-7.71 ppm) and in the gamma-ray wavelengths deduc ed from a revised estimate of the lattice spacing of Si crystals (+1.91 ppm ). On this revised energy scale, the strong line from Au-198 has an energy of 411 802.05 +/- 0.17 eV, which is 2.4 eV (or 5.80 ppm) lower than the 197 9 value. A significant improvement has come from the reduction in the uncer tainty in the wavelength-to-keV conversion factor from 2.6 to 0.3 ppm. The gamma-ray energies reported here are all on this 'wavelength' scale and ran ge from 25 to 6129 keV. The criteria for the selection of gamma rays to inc lude are described. The list of gamma-ray energies recommended for calibrat ion, especially for Ge semiconductor detectors, has values for about 260 ga mma-rays from 50 radionuclides and two (n, gamma) reactions. (C) 1999 Elsev ier Science B.V. All rights reserved.