TRUE-COINCIDENCE CORRECTION FOR FIELD GAMMA-RAY SPECTROMETRY IN AUGERHOLE COUNTING GEOMETRY

When absolute calibration of gamma-ray spectrometry in auger hole coun ting geometry is aimed at, true-coincidence effects of the measured ga mma-rays should be corrected for. The calculational method developed i n the present work starts from modelling the auger hole counting geome try as an ''infinite'' Marinelli beaker, the finite dimensions of whic h are found by determining where ($) over bar Omega V versus H reaches a plateau (($) over bar Omega is the effective solid angle; V is the volume of the Marinelli beaker; H is the thickness of the cylindric ma ntle of the Marinelli beaker). Then, for the thus defined Marinelli be aker a coincidence correction factor (COI) is calculated - via a numer ical integration procedure - as the weighted mean of COIs for infinite simally thin source layers parallel to the detector surface, with the peak efficiency as the weighing factor. The effect on COI caused by th e special geometric position of the material extending below the back of the detector was taken into account. The method turned out to yield quite acceptably accurate results, as checked for the 1368.6 and 2754 .0 keV lines of Na-24 measured as an aqueous solution in a 23-1 Marine lli beaker on a 3 in. X 3 in. NaI(Tl) detector.