| When in-situγspectrometry is used to determine activity concentration of artificial radionuclide in soil, it is always confronted with the problem that the nuclide's depth-distribution shape and soil bulk-density is unbeknown. Therefore, many studies have been made to deduce the depth-distribution from in-situ spectrum, and there are two papers in print discussing the method of soil bulk-density determination by Peak-to-valley ratio of in-situγspectrum. However, there are some imperfects in the published papers, and no report was presented in public in China concerning these issues. In such case, research on the two techniques was performed in the paper, and the determination precision was improved greatly.At first, the developments and deficiencies of in-situγspectrometry were discussed in determining radionuclide's depth-distribution and soil bulk-density. Then, based on the requirements of environmental survey in one large-area site contaminated by artificial radionuclide, three methods were studied or established for determining the depth-distribution by in-situγspectrometry, including Peak-to-valley ratio method, Peak-to-peak ratio method and Delaminated method. Furthermore, theoretical research was done to estimate the method-sensitivities and relationships among these methods. Finally, the in-situγspectrometric technique for determining the soil bulk-density was studied.The main results are as follows:1) The depth-distribution shape of radionuclide and soil bulk-density's influences to the in-situγspectrometry were described by mathematical analysis. And the technical deficiencies were discussed and revealed also when using terms of"Mass depth"or"Equivalent surface deposition"to describe the distribution of artificial nuclide in soil.2) Based on the attenuation principle ofγ-rays in soil,"Peak-to-peak ratio method"was studied to determine the depth-distribution of multiple-energyγradionuclide deposited in soil. The method has been used to determine the 125Eu deposited in soil in our work, and the influence of soil bulk-density to the method was corrected successfully.3)"Delaminated method"was established in the paper based on the attenuation principle ofγ-rays in soil, and the related ill-conditioned equations were resolved well also. The method is robust to determine the multiple-energyγradionuclide with complicated depth-distribution shape, and has been used to determine non-deposited 152Eu in soil. The unique advantage of Delaminated method is that neither the prior knowledge of depth distribution shape of nuclide nor an unwieldy lead collimator is required.4) Based on the scattering principle ofγ-rays in soil,"Peak-to-valley ratio method"was studied to determine the depth-distribution of singleγradionuclide deposited in soil, such as 137Cs. Numerical calculation theory and Monte-Carlo simulation method of"scatter-fraction factor", stripping method and stripping parameter was established, which made the Peak-to-valley ratio method more perfect than the ago.5) Sensitivities, practicabilities and relationships of the three methods for determination of nuclide's depth-distribution have been studied and estimated.6) Based on the scattering principle ofγ-rays in soil, theory about the relationships between"Peak-to-valley ratio"and"Soil bulk-density", and dimension of symmetry volume-source was established, and the theoretical correctness was validated by experiments. The new theory established in the paper revised the conclusion of Tyler(2001,2004) that"soil bulk-density can be determined through the PVR information of natural in-situγspectrum".
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