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[en] This paper describes the influence of landform on measuring results of a vehicle in-situ HPGe γ spectrometer. Taking ¹³⁷Cs as an example, the relative deviation between calculated values and measuring ones of specific activity was obtained by Beck expression and theoretical model approximation. The results show that under the condition of three landforms in this paper, assuming uniform distribution of ¹³⁷Cs in soil, the influence of landform on measuring results of an in-situ HPGe γ spectrometer is less than 20% when the measuring altitude is 4 m. The influence of landform on measuring results decreases as measuring altitude increases. (authors)

[en] [Background] The inversion of gamma spectrum by maximum likelihood method can effectively improve the energy resolution of gamma spectrum. [Purpose] This study aims to observe the ability of maximum likelihood method to retrieve the central channel of γ characteristic peaks. [Methods] Monte Carlo simulation program MCNP (Monte Carlo N Particle Transport Code) was used to calculate the energy response matrix of a 10.16 cm × 10.16 cm × 40.64 cm NaI(Tl) detector. Energy response matrix, the simulated spectra contained 10 different peaks, and the ¹⁵²Eu γ spectra obtained by the experiment were retrieved. [Results and Conclusions] The results showed that the maximum deviation of the peak center channel between the retrieved spectra and the simulated spectra was 1 channel, deviation between the retrieved spectrum and ¹⁵²Eu γ spectrum measured in the lead shielding room was less than 2 channels, the deviation between the retrieved spectrum and ¹⁵²Eu γ spectrum measured in the laboratory's natural environment was less than 4 channels. (authors)

[en] [Background] The phenomenon that right is higher than left in full-energy peak of the γ spectrum in the high active sample using HPGe gamma-ray spectrometry in laboratory, brings error into the gamma-radioactive nuclide analysis. [Purpose] This paper aims to explain the phenomenon to realize accurate quantitative analysis. [Methods] The theoretical formula of the right-to-left ratios was developed, and experiment was designed to prove it. [Results] The experiment indicates that the theoretical calculation is right. The research achievement shows that the phenomenon is caused by accidental coincidence. [Conclusion] The right-to-left ratios increase first, then decrease with the higher dead time. When the dead time is lower than 1.0%, the right is approximate equal to the left in full energy peak. With the dead time is higher than 1.0% and lower than 4.0%, the ratios increases with the dead time. As the dead time is higher than 4.0% and lower than 56%, the ratios decreases with the dead time. Comparing the experiment with LabSOCS, it indicated that the phenomenon has no influence on analysis of the point source. (authors)

[en] Deadtime corrections of three in-situ HPGe γ spectrometers were studied by experimental method of interference-method with strong γ source. The linear relationships between the percent deadtime and the correction coefficients were fitted by the least-square-method. The comparisons between the experimental results and the automatic correction values of full-energy-peak count rates were performed. The results show that the maximum deviation of the automatic correction values relatively to the experimental results is less than 4.4%.It indicates that in the deadtime range of 1.13%-52.95%, the automatic correction results of deadtime by these spectrometers themselves are exact and the deadtime correction techniques of modern γ spectrometers are efficacious, which can be used in the data analysis of γ spectra. (authors)

[en] Using MCNP simulation calculation, the influence of the structural size change of the coaxial high-purity germanium detector on the detection efficiency is obtained. Combined with the specific experimental data and the obtained rule recognition, adjust the crystal radius, the crystal-to-window distance, the cold refer hole length and the dead layer thickness, so that the adjusted analog structure is suitable for all source distances. Using the adjusted structure, the relative deviation between the simulated value of the detection efficiency and the experimentally calculated value is less than 3.68%. (authors)

[en] A kind of in-situ measurement method is introduced in this paper, by which the radioactivity in the clayey sand of ground surface contaminated by radioactive particulates can be investigated. In the experiments, the circular plane regions whose radius is r are concerned, and the thickness of contaminated layer is l; the detector is mounted above the centre of circular plane region, and it's height is h. The teckmique called 'sampling deduction' was used in the measurements. At one spot, the first in-situ measurement was performed directly, then the second measurement was carried out after the contaminated layer were wiped out and filled with 'clean clayey sand' (in which there were no ¹³⁷Cs). The radioactivity of contaminated layer was calculated through the net count rate of the second measurement which was subtracted from the first measurement. The contaminated layer samples which were wiped out are collected overall for laboratorial measurement and analysis. When r, h and l were 0.80 m, 0.50 m and about 0.02 m respectively, the results showed that the maximum deviation of ¹³⁷Cs was 37 percent when making the comparison of measuring results betwean labomtorial analysis and the in-situ measuremert method. (authors)

[en] This paper presents an on-site monitoring technique for carborne radioactive waste container, including theoretic model and efficiency calibration method. Three portable HPGe detectors are used to scan three surfaces of the carborne waste container. And then the weighted average is performed to get the average specific activity of the interested nuclides. The experiments which turned out the necessity of scanning three surfaces successfully were completed with uniform and non-uniform volumetric sources on the ideal condition. When the measurement time is 1000 s, the MDAs of "2"4"1Am, "1"3"7Cs, "6"0Co and "1"5"2Eu are 170 Bq/kg, 1 Bq/kg , 1 Bq/kg and 5 Bq/kg, respectively. And the uncertainty is less than 40%(1σ) for "2"4"1Am, 35%(1σ) for "1"3"7Cs,"6"0Co and "1"5"2Eu. Compared with the other techniques, transmission source device and collimators are not required, and the assay time is shorter. However, the limitations of this technique are that measurement results are not radionuclide activity for every voxel but specific activity for the whole container, and that it is difficult to measure for the low energy gamma emitters (e.g. "2"4"1Am) in the waste with high density matrix based on gamma-assay method. (authors)

[en] It is difficult to produce the radioactive standard gas source such as ¹³³Xe, which makes the calibration of g spectrometers difficult. The uniform falling velocities of the ¹³³Ba disk source and ¹³⁷Cs point source were used to calibrate the detection efficiency of ¹³³Xe volume source and ¹³⁷Cs linear source. The non-uniform falling velocities of ¹³³Ba disk source and ¹³⁷Cs point source were used to calibrate the detection efficiency of heterogeneous ¹³³Xe volume source and heterogeneous ¹³⁷Cs linear source. The results show that the detection efficiencies of ¹³³Xe were 0.155 (for ϕ46.8 mm × 20 mm sample) and 0.143 (for ϕ63.5 mm × 20 mm sample) respectively, obtained for the uniform falling velocity of the source, and the uncertainty was 8.4% (k = 2). The deviation between the efficiency of the heterogeneously distributed volume source and the efficiency of uniform volume source in 14%, and 23% for linear sources. Therefore, the deviation caused by heterogeneity must be corrected. (authors)

[en] The development and productions are presented in brief about the applied technologies of in-situ γ spectrometry in our laboratory, including mainly: detection efficiency calibration method, measurement method of the depth-distribution of artificial radionuclides is soil, air absorbed γ dose rate measurement, measurement method of radionuclides in the air, measurement method to the unsymmetrical radioactive achieved in the study, should have important values in the measurement and survey of radioactive environment. (authors)