Calculations of the corrections for the true summation of cascade γ rays on the basis of statistical simulation using evaluated nuclear data

Abstract

A method of calculating the corrections to the true summation of the γ radiation for arbitrary radionuclides for measuring point and volume sources using scintillation and ultrapure germanium detectors is described. The calculations are based on the Monte Carlo method using ENSDF evaluated data on the structure of atomic nuclei. An experimental check made using IAEA test spectra confirms that the calculations of the correction factors are reliable. The method is integrated into the γ spectrometric packages LSRM-2000 and AkWin, where the corrections for the ture summation are used for developing a library.The increase or decrease in the number of counts recorded in the total-absorption peaks as a result of summing the impulses at the exit of a detector can strongly influence the accuracy of the results of γ spectrometry. Taking account of this effect is now one of the mandatory requirements for modern γ-spectrometric software.The effect appears in measurements of radiation from cascade sources and is due to the summation of impulses while simultaneously detecting two or more γ rays in the sensitive volume of a detector. This distorts the measured γ-ray spectrum, specifically, it changes the areas of the total-absorption peaks, deforms the continuous Compton distribution, and results in the appearance of spurious peaks in the energy, which are absent in the true emission spectrum of the source.In contrast to the random summation, where the probability of detecting impulses simultaneously is proportional to the squared counting rate at the entrance into the spectrometric channel, the intensity of true summation is determined by the measurement geometry, the characteristics of the detector, and the special features of the radionuclide cascade scheme. The difficulty of introducing corrections for the true summation is due, first and foremost, to the fact that it is necessary to know the γ-ray detection efficiency along the total-absorption peak and the total efficiency which depends on the relative arrangement and configuration of the source and detector, as well as of the environment in which scattering and backward reflection of γ rays occur. The problem is exacerbated during measurement of radiation from a volume source, which effectively absorbs and scatters its own radiation.An accurate calculation requires taking into account the possible anisotropy of the angular distribution of the emitted cascade photons. In addition, the coincidence of γ radiation with annihilation (511 keV) photons must be taken into account when measuring a source of β + radiation. A coincidence of the γ radiation from the source and the characteristic and

Cross sections for fast-neutron interaction with Lu, Tb, and Ta isotopes

“…Correction values were taken as the ratio of the detector efficiency for point and volume radiation sources. Corrections for observed coincidence summing were calculated with the Nuclide Master+ code [12]. The input information for these calculations was the real geometry of the measurements and the nuclear structure parameters from ENSDF [13].…”