ESTABLISHING AN ENERGY SCALE FOR PULSE-HEIGHT DISTRIBUTIONS FROM GAMMA-RAY SPECTROMETERS BASED ON INORGANIC SCINTILLATORS

摘要

Devices, experiment designs, and data analysis techniques useful for the calibration of scintillation gamma-ray spectrometers are criti¬cally examined. Though the ideas have broader application, the discus¬sion assumes the use of NaI(Tl) phosphors. The review of calibration sources includes tables of gamma-emitting radioisotopes employable for this purpose, with best energies, uncertainties, and other convenient data. The branching ratios among the naturally mixed x-ray lines (K-L vs K-M + K-W) are tabulated for useful radioisotope x-ray sources to enable use of a simple method given for determining the appropriate "effective" energy of the mixed source. The origins of spectrometer instability and nonlinearity are reviewed along with their relative importances, and defensive experiment designs and data analysis techniques are discussed. For finding the central position of the peak in a pulse-height distribution from gamma rays of a single energy, all the standard numerical and graphical methods are illustrated and compared, including full and partial nonlinear least-squares analyses. Finally, interpola¬tion methods are detailed for determining from the available calibration information an unknown gamma-ray energy and its uncertainty.