Influence and correction of self-absorption of cylindrical samples on HPGe γ-spectrum measurement results
Objective To analyze the influence of the self-absorption effect of different density samples on the measurement results of HPGe γ-spectrometer,and discuss the correction method of the cylindrical sample self-absorption in the measurement of HPGe γ-spectrometer.Methods Ten kinds of samples with different densities were measured by HPGe y-spectrometer,and the national standard material of thorium powder and uranium-radium balance powder were added in the samples.The γ-ray energy points of 232Th and 226Ra in the sample spectrum were analyzed,and the relative self-absorption factor(F)was calculated according to the activity formula.The correction curve was fitted with the density of cylindrical samples and the relative self-absorption coefficient,and the self-absorption coefficient was calculated by the mass attenuation coefficient of γ-ray of a known substance for verifying the accuracy of the self-absorption curve that fitted before.Results There were no statistical differences(P＞0.05)between the mean values of the energy points of y-rays count rate in the samples added thorium of 238.6 keV(t=-2.128),338.7 keV(t=-2.002),583.1 keV(t=-2.086),911.2 keV(t=-2.165)and that in the samples added aluminum powder of 295.2 keV(t=-1.541)、351.9 keV(t=-1.557)、609.3 keV(t=-1.498)and 1 120.3 keV(t=-1.688).The differences were not statistically significant.When the density of cylindrical sample is different from that of calibration source,the relative self-absorption coefficient deviation was greater with the density difference.The relative self-absorption coefficient decreased with the increase of γ-ray energy.All deviations of self-absorption coefficient of energy points calculated by formula and that measured by experiment were less than 10％.Conclusions If the difference exists between the density of the sample and the calibration source,the self-absorption correction should be carried out.If the densities are same,the effect of self-absorption is greater in the low energy region than that in the high energy region.The result got by experimental measurement is more reliable than that calculated by formula.The self-absorption correction curve of the cylindrical sample fitted in this experiment can be used for daily measurement correction in the laboratory.
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