In situ gamma-spectrometry several years after deposition of radiocesium

Abstract

A new method is introduced for deriving radiocesium soil contaminations and kerma rates in air from in situ gamma-ray spectrometric measurements. The approach makes use of additional information about gamma-ray attenuation given by the peak-to-valley ratio, which is the ratio of the count rates for primary and forward scattered photons. In situ measurements are evaluated by comparing the experimental data with the results of Monte Carlo simulations of photon transport and detector response. The influence of photons emitted by natural radionuclides on the calculation of the peak-to-valley ratio is carefully analysed. The new method has been applied to several post-Chernobyl measurements and the results agreed well with those of soil sampling.

Efficient in situ method to determine radionuclide concentration in soil

“…Gering et al [6] similarly assumed a vertical distribution function and determined the parameters by a comparison of the empirical peak-tovalley ratio with the theoretical ratio determined in a simulation of both photon transport and consecutive energy deposition in the detector. Jacob and Thummerer [7] implemented a similar procedure.…”

Monitoring Radioactivity in the Environment Under Routine and Emergency Conditions

“…The uncertainty of the measurement is influenced by local topographic variations (buildings, trees,…), by vegetation cover and by the vertical activity distribution of the radionuclide. Good results have been obtained by means of an advanced analysis of the measured gamma spectrum, referred to as 'Peak-to-valley' method (Gering et al, 1998;Tyler, 2004). In-situ measurements are also common practice in emergency preparedness networks where gamma dose-rate detectors (usually Geiger-Müller probes, proportional counters, ionisation chambers) monitor continuously the ambient gamma dose-rate.…”

Experimentally determined vs. Monte Carlo simulated peak-to-valley ratios for a well-characterised n-type HPGe detector

“…Zombori et al (1992) calculated the ratio between the net peak area and these valley counts as a way of estimating the penetration depth of the 137 Cs in radioactive fallout (Zombori, 2012(Zombori, , 2013. Several others have used this method and evaluated the feasibility in different situations (Feng et al, 2009;Gering et al, 1998;Hjerpe and Samuelsson, 2002;Kastlander and Bargholtz, 2005;Panza, 2012;Lemercier, 2007;Tyler, 2004). The contribution in the valley ROI is dependent of detector characteristics, and to further develop the PTV method, a better understanding of contributing factors is necessary.…”