Dynamics of decrease of the gamma dose rate in air in rural settlements of the Bryansk region (Russia) in the remote period after the Chernobyl accident

The aim of this study was to determine the dynamics of decrease of the dose rate of gamma radiation in air from 137Cs in typical rural locations in the remote period after the Chernobyl accident. The dose rate measurements were performed in the areas of 15 settlements of the Zlynka, Klintsy and Novozybkov districts of the Bryansk region of Russia in the period 1998–2012. After the accident in 1986, the density of contamination of the territory with 137Cs in all settlements was higher than the value of 555 kBq/m2 . Monitoring measurements of the dose rate were performed in eight locations commonly used in assessing the radiation doses to the rural population after the Chernobyl accident: 1) virgin soils (meadows) located outside settlements, 2) virgin soils located inside settlements, 3) forests, 4) arable fields, 5) kitchen gardens, 6) other ground surfaces (earthen yards next to residential buildings), 7) single-story wooden houses, 8) asphalted areas (streets, roads, courtyards next to residential buildings). The number of observation sites in individual locations ranged from 6 to 19 (a total of 103 sites). Series of measurements at individual sites were launched in the period 1998–2001 and completed in 2009–2012. On average, the duration of the series was 11.1 years. The measurements were made in the spring-autumn period annually (in some years at some sites two to three times a year) using a portable gamma-ray spectrometer-dosimeter. In the initial period of the study (1998–2001), the values of the absorbed dose rate in air from 137Cs were in the range from 40 to 2020 nGy/h. The maximum values were recorded in virgin meadows and forests, and the minimum ones were observed inside houses and over asphalted surfaces. By the end of our series of observations (2009–2012), the dose rate decreased at all sites, by an average of 33% (range 6–64%). The values of the ecological period of half-reduction of the dose rate, calculated for individual sites, ranged from 14 to 320 years and averaged 34 years (virgin soils located outside settlements), 30 years (virgin soils located inside settlements), 37 years (forests), 93 years (arable fields), 99 years (kitchen gardens), 33 years (other earth surfaces), 45 years (wooden houses), 60 years (asphalted areas). The deduced values of the rate of decrease of the dose rate of gamma radiation in the air in the surveyed locations were used to estimate the ecological period of the half-reduction of the effective external dose for rural population living in wooden houses. On average, this period was equal to 50 years. Given the radioactive decay of 137Cs, we can expect that the external dose from Chernobyl 137Cs to the rural population will decrease by approximately 4% per year. Our estimate of the rate of decrease of the external effective dose from 137Cs in the remote period after the Chernobyl accident is in agreement with the estimates that were previously given by other authors for the slow component of decreasing external doses from 137Cs to adults living in rural settlements of the Bryansk region.

Chernobyl, 137Cs, gamma radiation, absorbed dose rate in air, effective dose

1. Golikov VYu, Balonov MI, Jacob P. External exposure of the population living in areas of Russia contaminated due to the Chernobyl accident. Radiation and Environmental Biophysics. 2002;41(10): 185–193.

2. Radiological and Hygienic Issues of the Mitigation of the Chernobyl NPP Accident Consequences. Eds.: Onishchenko GG, Popova AYu. St.-Petersburg Research Institute of Radiation Hygiene after Professor P.V. Ramzaev. 2016; 1. 448 p. (In Russian).

3. Bruk GYa, Bazyukin AB, Barkovsky AN, Bratilova AA, Vlasov AYu, Goncharova YuN, et al. The exposure for populations of the Russian Federation due to the Chernobyl accident and main directions of further work in the coming period. 2014;7(4): 78–83 (In Russian).

4. Bruk GYa, Bazyukin AB, Bratilova AA, Yakovlev VA. Trends of development and prediction of the doses from the internal exposure of the public of the Russian Federation and its critical groups in the distant post-Chernobyl NPP accident period. Radiatsionnaya Gygiena = Radiation Hygiene. 2019;12(2) (Special issue): 66–74 (In Russian).

5. Jacob P, Prohl G, Likhtarev I, Kovgan L, Gluvchinsky R, Perevoznikov O, et al. Pathway Analysis and Dose Distributions. European Commission, Brussels: 1996. EUR 16541 EN. 130 p.

6. Ramzaev V, Yonehara H, Hille R, Barkovsky A, Mishine A, Sahoo SK, et al. Gamma-dose rates from terrestrial and Chernobyl radionuclides inside and outside settlements in the Bryansk Region, Russia in 1996–2003. Journal of Environmental Radioactivity. 2006;85: 205–227.

7. Golikov VYu. Analysis of the long-term dynamics of external doses of the population after the Chernobyl accident. Radiatsionnaya Gygiena = Radiation Hygiene. 2018;11(4): 39–50.

8. Balonov MI, Savkin MN, Pitkevich VA, Schukina NV, Podleschuk VB, Ogorodnikova GV, et al. Mean effective cumulated doses. Radiation and Risk. 1999;(Special issue): 1–125 (In Russian).

9. Bruk GYa, Balonov MI, Golikov VYu, Bazyukin AB, Romanovich IK, Shutov VN, et al. The average effective doses accumulated during 1986–2005 for the residents of the settlements of the Bryansk, Kaluga, Oryol and Tula regions of the Russian Federation, assigned to the zones of radioactive contamination by decree of the Government of the Russian Federation No. 1582 of December 18, 1997 “On approval of the list of settlements located in the boundaries of the zones of radioactive contamination due to the catastrophe at the Chernobyl nuclear power plant. Radiation and Risk. 2007;16(1): 3–73 (In Russian).

10. Bruk GYa, Bazyukin AB, Bratilova AA, Vlasov AYu, Goncharova YuN, Gromov AV, et al. The average annual effective doses for the population in the settlements of the Russian Federation attributed to zones of radioactive contamination due to the Chernobyl accident (for zonation purposes), 2014. Radiatsionnaya Gygiena = Radiation Hygiene. 2015;8(2): 32–128 (In Russian).

11. MKS-SK1 «SKIF» x-ray and gamma radiation spectrometer-dosimeters. – Available from: https://all-pribors.ru/ opisanie/19630-00-mks-sk1-skif-14822 [Accessed 09 November 2019] (In Russian).

12. Ramzaev VP, Barkovsky AN. On the relationship between ambient dose equivalent and absorbed dose in air in the case of large-scale contamination of the environment by radioactive cesium. Radiatsionnaya Gygiena = Radiation Hygiene. 2015;8(3): 6–20.

13. Ramzaev VP, Golikov VYu. A comparison of measured and calculated values of air kerma rates from 137Cs in soil. Radiatsionnaya Gygiena = Radiation Hygiene. 2015;8(4): 42–51 (In Russian).

14. Ramzaev V, Barkovsky A, Mishine A, Andersson KG. Decontamination tests in the recreational areas affected by the Chernobyl accident: efficiency of decontamination and long-term stability of the effects. Journal of the Society for Remediation of Radioactive Contamination in the Environment. 2013;1(2): 93–107. Available from: http:// khjosen.org/journal/FullText/Vol1/V1N2-RAMZAEV-full.pdf [Accessed 12 December 2019].

15. Roed J, Lange CL, Andersson KG, Prip H, Olsen S, Ramzaev V, et al. Decontamination in a Russian Settlement. Ris National Laboratory report Risø-R-870 (EN). Risø National Laboratory, Roskilde, Denmark. 1996. Available from: https://inis.iaea.org/collection/NCLCollectionStore/_Public/27/053/27053487.pdf?r=1&r=1 [Accessed 12 December 2019].

16. Bailiff IK, Slim HA. Development of reference database for gamma dose assessment in retrospective luminescence dosimetry. Radiation Measurements. 2008;43: 859–863.

17. Golikov V, Wallström E, Wöhni T, Tanaka K, Endo S, Hoshi M. Evaluation of conversion coefficients from measurable to risk quantities for external exposure over contaminated soil by use of physical human phantoms. Radiation and Environmental Biophysics. 2007;46(4): 375–382.

18. Thornberg C, Vesanen R, Wallström E, Zvonova I, Zhesko T, Balonov M, et al. External and internal irradiation of a rural Bryansk (Russia) population from 1990 to 2000, following high deposition of radioactive caesium from the Chernobyl accident. Radiation and Environmental Biophysics. 2005;44(2): 97–106.