[en] Airborne radiation survey is the only effective technology when nuclear accident has happened, and rapid survey of the contaminated areas is needed. In this article, available instruments used in China and all over the world, and the instrument best suit for this task were analyzed. Based on the analysis, minimum detectable activities (MDAs) of "1"3"7Cs and "1"3"1I measured by GRS-16 in China were calculated according to the results obtained by accumulative calibration of small sources. Forth more, MDAs of more advanced airborne radiation survey instrument were calculated according to the relative article and Monte Carlo simulation. At last, differences between various instruments were analyzed. (authors)

[en] The onsite monitoring model for the carborne radioactive waste container was established. However, the formula derivative and the correlation coefficients between influence factors were difficultly calculated through analytical method because of the complexity of formula, so the evaluation of uncertainty was difficult based on the transfer law of uncertainty. The uncertainties for the monitoring results of carborne radioactive waste container were evaluated by the Monte Carlo synthesis method, and this method resolve the problem of the uncertainty assessment for the In-situ γ measurement. The processes of evaluation were that uncertainties of the parameters were completed with A and B species method, then the combine uncertainties were obtained with Monte Carlo synthesis method. The results indicated that the relative uncertainty was less than 40% (1 σ) for ²⁴¹Am, 34% (1 σ) for ¹³⁷Cs, ⁶⁰Co and ¹⁵²Eu. (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] The main limitation of in-situ γ spectrometry lies in determining the depth-distribution of the artificial radionuclide in soil. Many researchers have developed methods and models for deducing the depth-distribution information from in-situ spectrum itself. Until now, such methods were studied and established as “Multiple photopeak method”, “Peak-to-valley ratio method” and “Collimation or lead-plate method”. This paper presented the comparative theoretical study on the relaxation-depth sensitivity. The experimental methods for Multiple photopeak, Peak-to-valley ratio and Collimation or lead-plate are at energies of 244 keV and 1408 keV γ-rays of ¹⁵²Eu, 662 keV γ-ray of ¹³⁷Cs, 662 keV γ-ray of ¹³⁷Cs, respectively, and the In-situ object counting system was employed in Collimation or lead-plate method. Results indicated that the sequence of relaxation-depth sensitivity from the maximum to the minimum was as following: Peak-to-valley method, Multiple photopeak method, and Collimation or lead-plate method, and the sensitivity of Collimation or lead-plate method was far less than Multiple photopeak method. (author)

[en] The peak-to-valley ratio (PVR) method was approached to determine the depth distribution of ¹³⁷Cs of PVR is much sensitive with the dissimilarity of radioactive depth distribution, and the influence of soil density uncertainty to PVR is slight and can be neglected when the variation of soil density is within 10%. Field experiments were performed to justify the theories as correctness. The results show that the maximum relative deviation of in-situ γ spectrometry is about 31% relative to the samples analysis in laboratory, which indicates that PVR method of in-situ γ spectrometry is correct for the determination of radioactive depth distribution in soil. (authors)

[en] It presents the specific relationship between soil bulk density and peak-to-valley ratio (PVR) of natural radionuclides in situ γ spectra, by theoretical deduction, Monte Carlo simulation and experimental research. Results show that for an infinite half-space volume source, PVR is a constant independent of the diverse soil bulk density. But for a limited-scale volume source, PVR would decrease slowly with an increase in soil bulk density, and the smaller the source scale, the larger the PVR variation with soil bulk density. However, the PVR variation with bulk density is very small in general. For field measurements, the volume source thickness is uncontrollable in practice, and the volume source radius should not be as small as needed for the limitation of low detection efficiency. Hence the soil bulk density could not be determined through the information from PVR of field in situ γ spectra. And the results reveal the conclusions of 'soil bulk-density can be determined through the PVR information of natural in-situ γ spectra', and 'study on the law of low-energy γ spectra discovers the relationships between the characteristics of shape and the effective atomic number and the density of the material', should be revised by the new theory established in the paper; But it is discovered also that the mass thickness of an ideal isolated wall can be determined by the PVR method, which is very sensitive when the wall's mass thickness is not very large. (authors)

[en] This paper presents the specific relationship between soil bulk density and peak-to-valley ratio (PVR) of natural radionuclides in in situ γ spectra, by theoretical deduction, Monte Carlo simulation and experimental research. Results show that for an infinite half-space volume source, PVR is a constant independent of the diverse soil bulk density. But for a limited-scale volume source, PVR would decrease slowly with an increase in soil bulk density, and the smaller the source scale, the larger the PVR variation with soil bulk density. However, the PVR variation with bulk density is very small in general. For field measurements, the volume source thickness is uncontrollable in practice, and the volume source radius should not be as small as needed for the limitation of low detection efficiency. Hence the soil bulk density could not be determined through the information from PVR of field in situ γ spectra. (authors)

[en] An effective method was established for the radioactive anomalies discrimination by carborne Nal (Tl) γ spectra based on the principles that the second singular value of Noise Adjusted Singular Value Decomposition (NASVD) was sensitive to the changes of the background, and that the adjacent background spectra of scanning measurement were similar. In this method, NASVD was used for the noise reduction of spectra, anomalies discrimination, and the reconstruction and stripping of background spectra, then the anomalies display was done in rainbow method. This method was used successfully in the discrimination and display of the radioactive anomalism. (authors)

[en] The main limitation of in-situ γ spectrometry lies in determining the depth-distribution of the artificial radionuclide in soil. So, many researchers have developed methods and models aimed at deducing the depth-distribution information from in-situ spectrum itself. Until now, there are three main methods studied and established, which includes 'Multiple photopeak method', 'Peak-to-valley ratio method' and 'Collimated or lead plate method'. This paper presented the theoretical study on the method-sensitivity comparison. The experimental methods for Multiple photopeak, Peak-to-valley ratio and Collimated or lead plate are at the energy of 244 keV and 1 408 keV γ-rays of ¹⁵²Eu, 662 keV γ-ray of ¹³⁷Cs, 662 keV γ-ray of ¹³⁷Cs, respectively,and the ISOCS was employed in Collimated or lead plate method. Results indicated that the sequence of method-sensitivity from the maximum to the minimum was as following: Peak-to-valley method, Multiple photopeak method, and Collimated or lead plate method, and the sensitivity of Collimated or lead plate method was far less than Multiple photopeak method. (authors)