SPATIAL DISTRIBUTION OF SOME RADIONUCLIDES MEASURED IN MOSSES COLLECTED OVER LARGE AREA

1. SPATIAL DISTRIBUTION OF SOME RADIONUCLIDES MEASURED IN MOSSES COLLECTED OVER LARGE AREA M. Krmar1, D. Radnović2, M. Mesaroš3, J. Hansman1, ŽMedić1 1 Physics Department, Faculty of Science, University Novi Sad, Novi Sad, Serbia 2 Department of Biology and Ecology, Faculty of Science, University Novi Sad, Novi Sad, Serbia 3 Geography Department, Faculty of Science, University Novi Sad, Novi Sad, Serbia

2. In 2015 moss samples were collected at 196 locations in Serbia It was an excellent possibility to use terrestrial mosses to get spatial distribution of some measurable radionuclides over a relatively large area

3. Some preliminary results were already published, however with a small number of collected samples. 7Be 137Cs M. Krmar, D. Radnovic, S. Rakic, M. Matavuly: Possible use of terrestrial mosses in detection of atmospheric deposition of 7Be over large areas, Journal of Environmental Radioactivity, 95, (2007) 53-61

4. Measurements, previous experiences: In a standard cylindrical geometry (d = 61 mm, h = 64 mm), about 40 g of dry moss material should be measured up to 80 ks using HPGe detector having relative efficiency about 30%, to get activity of 7Be (in Bq/kg) with uncertainty less than 10% half-life of 7Be is just 53.4 days

5. Old Compton suppression 9” x 9” NaI(Tl) detector was shielded by 200 mm of Pb, 1 mm of Sn and 1.5 mm of Cu

6. Efficiency 58.6 % for point source of 137Cs IAEA reference soil material packed in standard geometry (d = 61 mm, h = 64 mm)

7. Background spectra, t = 5000 s

8. Moss sample, t = 5000 s 210Pb, 46.5 keV + characteristic Pb x 7Be, 478 keV 40K, 1460 keV

9. Moss sample with subtracted background 210Pb, 46.5 keV + characteristic Pb x 7Be, 478 keV 40K, 1460 keV

10. Moss sample with subtracted background 212Pb, 239 keV 214Pb, 295 keV, 352 keV 214Bi, 609 keV 214Bi, 1120 keV 214Bi, 1764 keV 214Bi, 2204 keV

11. Some statistics 1764 kev gamma line was used for calculation of activity of 214Bi (226Ra? 238U?) Mdl – minimal detectable limit

12. Radionuclides from 238U chain are typical soil elements as well as 40K 7Be arrives from stratosphere and upper troposphere

13. The first doubt appears in this study: Average contents of 238U (and other daughters) in soil in Serbia is about 50 Bq/kg and 40K is 500 Bq/kg. Measured medians of 214Bi and 40K are similar, however the highest concentration of 214Bi in mosses is higher than 40K one.

14. Distribution of 40K measured activities looks like a kind of normal one Distribution of 214Bi measurement should be log-normal, however there are two separated groups of samples

15. Spatial distribution of 214Bi measured in moss samples

16. Cosmogenic 7Be is a natural tracer not altered by anthropogenic activities Once produced, 7Be atoms are almost immediately adsorbed onto aerosol particles Aerosol particles are the most important reservoir of air pollutants, 7Be can be used in tracking their atmospheric paths and fall-outs.

17. 7Be is mainly formed in the stratosphere (about 67%) and higher layer of the troposphere (remaining 33%). Variations in 7Be production are associated with changes of the cosmic ray flux Cannizzaro, F., Greco, G., Raneli, M., Spitale, M.C., Tomarchio, E., 2004. Concentration measurements of 7Be at ground level air at Palermo, Italy – comparison with solar activity over period of 21 years. Journal of Environmental Radioactivity 72, 259-271

18. Seasonal variations are determined by interactions between upper troposphere and lower stratosphere, precipitations, winds, etc. Air sampling and precipitation can provide good evidence on radionuclide concentration or variations during a long time period at one fixed place. Comparable results can be obtained using mosses as a medium. M. Krmar, D. Radnovic, D.T. Mihailivic, B. Lalic, J. Slivka, I. Bikit: Temporal variation of 7Be, 210Pb and 137Cs in moss samples over 14 month period, Applied Radiation and Isotopes (2009)

19. By the measurement of 7Be concentration in air and deposition, it is possible to investigate a number of factors affecting its distribution in the atmosphere: • - stratospheric intrusions in the troposphere • - vertical transport in troposphere • horizontal movement of air masses • residence time of aerosol particles in the troposphere, etc. • The spatial resolution of radionuclide distribution over a large area is limited by the number of air sampling or precipitation sampling centers. • Large – scale and high - resolution 7Be deposition map was never done before.

20. Measured values of 7Be activities in mosses vary in a relatively broad region (34 Bq/kg – 956 Bq/kg) Although production of 7Be in higher atmosphere should be roughly uniform (in the area the size of Serbia), measured values showed, that deposition can be apparently non-uniform. It looks like a kind of a normal distribution

21. The second doubt Normal vs. lognormal distribution Physical quantities that are expected to be a SUM of many independent and random variables are NORMAL Physical quantities that are expected to be a PRODUCT of many independent and random variables are LOGNORMAL 7Be is short-living, almost uniformly produced in higher atmosphere Distribution of 238U depends on geology, transport phenomena etc.

22. Small digression Indoor Radon gas concentration is maybe the most frequently studied log normal distribution

23. Small digression Moss survey Serbia 2005. Distributions of stable elements in mosses are almost always something between normal and lognormal.

24. Spatial distribution of 7Be measured in moss samples

25. The third and the most important doubt: • WHAT IS IT???? • Stable distribution of 7Be depending on geo – parameters? • Stable distribution depending on average meteorology conditions? • Fingerprint of stratospheric intrusion???

26. Thank you for your attention. Hope that you enjoy moss sampling, preparation, measurements etc. as we do.