FEATURES OF APPLICATION OF THE IN SITU AND EX SITU MEASUREMENT TECHNIQUES FOR DETERMINATION OF 137Cs SOIL CONTAMINATION

Abstract

In this paper we present the results of the ¹³⁷Cs soil contamination density measuring of the same area with using in situ and ex situ measurement techniques. The soil contamination density is understood as the activity of a radionuclide contained in a near-surface layer of soil with 20 cm thick per square meter of surface. Measurements were carried out during 2003–2015 on the territory of Shatsk Biologycal-Geographical Station of Lviv Ivan Franko National University located on the west bank of the Pisochne Lake (Shatsk district of the Volyn region). For measurements using the ex situ technique, a stationary gamma spectrometer equipped with a semiconductor Ge(Li)-detector was used, and for the measurements of the in situ technique, a gamma radiometer Virtuoso (manufactured by Sparing Vist, Lviv) equipped with a scintillation CsJ-detector. The obtained by both methods experimental results were used to create three-dimensional soil contamination maps of the investigated area with using the Surfer 8 program package.

The peculiarities of application, advantages and disadvantages of the use of both measurement technologies were analyzed. It has been shown that in the case of correct definition and application of coefficients that taking into account the absorption of gamma radiation of a radionuclide located in the depth of the soil, the results of in situ measurements with acceptable accuracy correlate with the results obtained with using of ex situ technique. Obtained by both methods results were shown a reliable picture of the distribution of radionuclide content in soils. The observed differences in the values of the minimum and maximum of radioactive contamination of investigated soils and the features of their sites localizations was explained both by the peculiarities of the measurement techniques and the natural decay of available in the soil radionuclide.

Using in situ method of the radiological measurements provides less time and simplicity of the analysis, their lower cost compared to the ex situ methodics. The acceptable reliability of the obtained results is ensured, if the adjusted coefficient values used by the application software packages for calculations are correctly applied.  It was shown that the received distributions of the soil radionuclide contamination density can somewhat vary depending on the method of their determination. It is concluded, in the result of using of both techniques of radiological measurements only a certain averaged evaluation, and not an exact picture of the soil radionuclide contamination density can been given in general.

Key words: in situ and ex situ techniques, gamma spectrometry, radioactive contamination, radiocaesium