THE INFLUENCE OF SOIL DENSITY AND THE CHARACTER OF RADIOACTIVE 134Cs And 137Cs POLLUTION’S DISTRIBUTION ON in situ MEASUREMENTS

Periodic radiation monitoring of soils today is a priority task not only for Belarus, but also for Japan, suffered by Fukushima nuclear power plant accident. Use of portable and light spectrometers with ability to perform in situ measurements makes it possible to quickly estimate specific activity of measured radionuclides with required accuracy in particular soil site. Basic information of a gamma radiation source (radionuclides content, effective radius of measurement area and thickness of contaminated layer) can be obtained directly during measurement. The purpose of this research is to test the feasibility of using algorithms for determination of specific activity and thickness of contaminated layer under conditions of soil measurement with variable density parameters and radiocesium distribution in soil.

Monte-Carlo simulating allowed to estimate the degree of deviation of the shape of simulated spectra obtained with the use of Monte-Carlo soil model with uniformly distributed radionuclide in it, and for the case when the radionuclide distribution by soil profile can be described by an exponential function. For these cases of natural distribution of radiocesium, the pulse-amplitude spectrum is formed by an effective thickness of the contaminated site, which contains more than 90 % of radionuclides.

The developed Monte-Carlo model of a probe and contaminated soil site allows to estimate the effect of the variability of soil density on the total count rate of the pulse-amplitude spectrum. As a result of theoretical estimations, the relationship between the effective radius of contaminated site is determined as a function of soil density.

Analysis of the influence of radial zones of the cylindrical gamma source on in situ gamma-spectrometer showed that the main contribution to the total count rate of the pulse-amplitude spectrum is made by the radial zone with radius of up to 40 cm from the center of the probe, regardless of the thickness of the contaminated layer in geometry «Probe is located on the soil surface». A small site facilitates the selection of measurement area of land with a sufficiently flat surface, which is desirable during surveying the territories, especially with complex terrain.

1. [On priority directions of scientific research of the Republic of Belarus for 2016–2020: Resolution of the Council of Ministers of the Republic of Belarus, March 12, 2015, no. 190]. Natsional'nyi reestr pravovykh aktov Respubliki Belarus [National Register of Legal Acts of the Republic of Belarus], 2015, no. 5/40254 (in Russian).

2. Izrael Y.A., Bogdevich I.M. Atlas sovremennykh i prognoznykh aspektov posledstvii avarii na Chernobyl'skoi AES na postradavshikh territoriyakh Rossii i Belarusi [Atlas of modern and predictive aspects of the consequences of the Chernobyl accident in the affected territories of Russia and Belarus]. Moscow–Minsk, Fund «Infosfera» – NIA Nature, 2009, 140 p. (in Russian).

3. Drovnikov V.V. Egorov M.V., Egorov N.Y., Zhivun V.M., Kadushkin A.V., Kovalenko V.V., Mamatov A.P. [In situ scintillation gamma spectrometry with fundamentally new capabilities. Some results of studies of the content of natural radionuclides in the ground]. ANRI, 2011, no. 1, pp. 56–64 (in Russian).

4. Tyler A.N. Monitoring anthropogenic radioactivity in salt march environments though in situ gamma-ray spectrometry. Journal of Environmental Radioactivity, 1999, no. 45, pp. 235–252. doi: 10.1016/S0265-931X(98)00110-6

5. Korun M. Likar A., Lipoglavsek M., Martincic R., Pucelj B. In situ measurement of Cs distribution in the soil. Nuclear Instruments and Methods in Physics Research. Section B, 1994, vol. 93, no. 4, pp. 485–491. doi: 10.1016/0168-583X(94)95638-3

6. Zombori P., Andrasi A., Nemeth I. A new method of determing radionuclide distribution in soil by in situ gamma-spectrometry. Hungarian Academy of Science, Central Research Institute for Physics, Institute for Atomic Research, Budapest, 1992, 35 p.

7. Zhukouski A., Mogi K., Kutsen S. [In situ measurement of soil radioactivity]. Vesti NAN Belarusi, Fiziko-tekhnicheskaya seriya [Proceeding of the National academy of sciences of Belarus, physico-technical series], 2016, no. 3, pp. 105–110 (in Russian).

8. Drovnikov V.V., Egorov M.V., Egorov N.Y., Zhivun V.M., Kadushkin A.V., Kovalenko V.V., Mamatov A.P. [A new method for determining the activity of gamma-ray sources behind a layer of an absorber with a priori unknown properties by the G-factor method]. ANRI, 2010, no. 3, pp. 9–15 (in Russian).

9. Mishra S. Sahoo S.K., Bossew P., Sorimachi A., Tokonami S. Vertical migration of radio-caesium derived from the Fukushima Dai-ichi Nuclear Power Plant accident in undisturbed soils of grassland and forest. Journal of Geochemical Exploration, 2016, no. 169, pp. 163–186. doi: 10.1016/j.gexplo.2016.07.023

10. Matsuda N. Mikami S., Shimoura S., Takahashi J., Nakanu M., Shimada K., Uno K., Hagiwara S., Saito K. Depth profiles of radioactive cesium in soil using a scraper plate over a wide area surrounding the Fukushima Dai-ichi Nuclear Power Plant Japan. Journal of Environmental Radioactivity, 2015, no. 139, pp. 427–434. doi: 10.1016/j.jenvrad.2014.10.001

11. Onda Yu., Kato H., Hoshi M., Takahashi Y., Nqueyn ML. Soil sampling and analytical strategies for mapping fallout in nuclear emergencies based on the Fukushima Dai-ichi Nuclear Power Plant accident. Journal of Environmental Radioactivity, 2015, no. 139, pp. 300–307. doi: 10.1016/j.jenvrad.2014.06.002

12. Briestmeister J.F. Ed. MCNPA general MonteCarlo N-particle transport code, Version 4A. Report LA12625-M, Los Alamos. NM, Los Alamos National Laboratory, 1994, 736 p.

13. ISO 18589-7. Measurement of radioactivity in the environment – Soil – Part 7: In situ measurement of gamma-emitting radionuclides, 2013, 54 p.

14. Zhukouski A. Kutsen S., Khrutchinsky A., Tolkachev A., Guzov V., Kojemiakin V., Chudakov V. [Evaluation of the area of influence of the contaminated soil region in solving the problems of radiation monitoring by in situ]. Devices and Methods of Measurements, 2014, no. 1 (8), pp. 119–124 (in Russian).

15. Ageyets V.Y. [Migration of radionuclides in the soils of Belarus]. Vesti NAN Belarusi, Seriya agrarnykh nauk [Proceeding of the National academy of scienc-es of Belarus, agrarian series], 2002, no. 1, pp. 61–65 (in Russian).

16. Appleby L.J., Dewell L., Mishara Yu.K. [The ways of migration of artificial radionuclides in the Environment. Radioecology after Chernobyl]. In F. Warner and Harrison (eds.). Moscow, Mir Publ., 1999, 512 p. (in Russian).

17. Silantiyev A.N., Shkuratov N.G., Bobovnikova Ts.I. [Vertical migration of radionuclides in the soil that fell as a result of the accident at the Chernobyl nuclear power plant]. Atomnaya energiya [Atomic energy], 1989, vol. 66, no. 3, pp. 194–197 (in Russian).

18. Ivanov Y.A. Lewyckyj N., Levchuk S.E., Prister B.S., Firsakova S.K., Arkhipov N.P., Arkhipov A.N., Kruglov S.V., Alexakhin R.M., Sandalls J., Askbrant S. Migration of 137Cs and 90Sr from Chernobyl fallout in Ukrainian, Belarus and Russian soils. Journal of Environmental Radioactivity, 1997, vol. 35, no. 1, pp. 1–21. doi: 10.1016/S0265-931X(96)00036-7

19. Bogdevich, I.M. Tarasiuk S.V., Novikova I.I., Dovnar V.A., Karpovich I.N., Tretyakov E.S. [Vertical migration of radionuclides 137Cs and 90Sr in soils of reserve lands and their availability by plants]. Vesti NAN Belarusi, Seriya agrarnykh nauk [Proceeding of the National academy of sciences of Belarus, agrarian series], 2013, no. 3, pp. 58–70 (in Russian).