Inertia in the response of radon monitors introduced by diffusion anti-thoron barriers

  • Dobromir Pressyanov Faculty of Physics, Sofia University “St. Kliment Ohridski”, Sofia, Bulgaria
Keywords: radon, thoron, thoron interference, inertia in response, radon monitors


The reduction of thoron (220Rn) influence on radon (222Rn) monitors by diffusion barriers may cause some deterioration of the quality of the radon measurements. Therefore, the best compromise has to be found between ensured anti-thoron protection and deterioration of the quality of the radon measurements. In this report, the focus is on the additional inertia in the response introduced by passive diffusion barriers against thoron. The characteristic inertia time introduced by diffusion barriers is theoretically modeled for the levels of thoron interference down to 1%. Experiments were carried out with an active monitor working in diffusion mode, using its built-in diffusion barrier and with an additional diffusion barrier added. The experimental results showed very good correspondence with the estimates based on the theoretical model. In summary, when using passive diffusion barriers against thoron, the greater is the reduction in the thoron interference, the larger is the inertia time in the response of active monitors that are introduced.


Download data is not yet available.


  1. Tokonami S. Why is 220Rn (thoron) measurement important? Radiat Prot Dosimetry 2010; 141: 335–9. doi: 10.1093/rpd/ncq246

  2. Council Directive 2013/59/EURATOM of 5 December 2013 laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation, and repealing Directives 89/618/Euratom, 90/641/Euratom, 96/29/Euratom, 97/43/Euratom and 2003/122/Euratom. Official Journal of the European Union L 13/17.1.2014.

  3. Pressyanov D, Mitev K, Dimitrova I, Georgiev S, Dutsov C, Michielsen N, et al. Report on the influence of thoron on radon monitors used in Europe including (i) procedures for checking their sensitivity to thoron, (ii) recommendations on the construction of radon monitors that are not sensitive to thoron and (iii) technical approaches aimed at reducing thoron-related bias in the radon signal in existing monitors. MetroRADON, Deliverable 2, 2020. Available from: [cited 11 January 2021].

  4. Csordás A, Fábián F, Horváth M, Hegedűs M, Somlai J, Kovács T. Preparation and characterisation of ceramic-based thoron sources for thoron calibration chamber. Radiat Prot Dosimetry 2015; 167(1–3): 151–4. doi: 10.1093/rpd/ncv234

  5. de With G, Kovács T, Csordás A, Tschiersch J, Yang J, Sadler SW, et al. Intercomparison on the measurement of the thoron exhalation rate from building materials. J Environ Radioact 2021; 228: 106510. doi: 10.1016/j.jenvrad.2020.106510

  6. Pressyanov D, Mitev K, Georgiev S, Dimitrova I, Kolev J. Laboratory facility to create reference radon + thoron atmosphere under dynamic exposure conditions. J Environ Radioact 2017; 166: 181–7. doi: 10.1016/j.jenvrad.2016.03.018

  7. Pornnumpa J, Oyama Y, Iwaoka K, Hosoda M, Tokonami S. Development of radon and thoron exposure systems at Hirosaki University. Radiat Environ Med 2018; 7(1): 13–20.

  8. Ward III WJ, Fleischer RL, Mogro-Campero A. Barrier technique for separate measurements of radon isotopes. Rev Sci Instrum 1977; 48: 1440–1. doi: 10.1063/1.1134915

  9. Sahoo BK, Sapra BK, Kanse SD, Gaware JJ, Mayya YS. A new pin-hole discriminated 222Rn/220Rn passive measurement device with single entry face. Radiat Meas 2013; 58: 52–60. doi: 10.1016/j.radmeas.2013.08.003

  10. Fleischer RL, Giard WR, Turner LG. Membrane-based thermal effects in 222Rn dosimetry. Radiat Meas 2000; 32: 325–8. doi: 10.1016/S1350-4487(00)00046-9

  11. Tommasino L. Concealed errors in radon measurements and strategies to eliminate them. Presented at the 8th Int. Conf. on Protection against Radon at Home and Work, Prague, 12–16 September 2016.

  12. Pressyanov D, Dimitrov D. The problem with temperature dependence of radon diffusion chambers with anti-thoron barrier. Rom J Phys 2020; 65: 801.

  13. Omori Y, Shimo M, Janik M, Ishikawa T, Yonehara H. Variable strength in thoron interference for a diffusion-type radon monitor depending on ventilation of the outer air. Int J Environ Res Public Health 2020; 17: 974. doi: 10.3390/ijerph17030974

  14. Pressyanov D, Dimitrov D, Dimitrova I, Georgiev S, Mitev K. Novel approaches in radon and thoron dosimetry. AIP Conf Proc 2014; 1607: 24–33. doi: 10.1063/1.4890699

  15. Durcik M, Havlik F. Experimental study of radon and thoron diffusion through barriers. J Radioanal Nucl Chem. Articles 1996; 209: 307–13. doi: 10.1007/BF02040465

  16. Mosley RB. Description of a method for measuring the diffusion coefficient of thin films to 222Rn using a total alpha detector. Proc. 1996 AARST International Radon Symposium 29.9–02.10.1996, Haines City, FL, USA.

  17. Holmgren O, Turtiainen T, Mitev K, Pressyanov D. Review of potential techniques and materials to reduce the influence of thoron on radon measurements and calibrations (2018). Available from: [cited 14 January 2021].

  18. Pressyanov D, Georgiev S, Dimitrova I, Mitev K, Boshkova T. Determination of the diffusion coefficient and solubility of radon in plastics. Radiat Prot Dosimetry 2011; 145: 123–6. doi: 10.1093/rpd/ncr069

  19. AlphaGUARD: portable radon monitor. User manual. Available from: [cited 14 January 2021].

How to Cite
Pressyanov D. (2022). Inertia in the response of radon monitors introduced by diffusion anti-thoron barriers. Journal of the European Radon Association, 3.
Special issue - European Radon Week 2020