PVR's variety with soil-bulk density in in-situ γ spectra of natural radionuclides

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)