RETROSPECTIVE RADON AND THORON MEASUREMENTS BY HOME STORED CDs/DVDs-RESEARCH AND PRACTICE

1. RETROSPECTIVE RADON AND THORON MEASUREMENTS BY HOME STORED CDs/DVDs-RESEARCH AND PRACTICE Dobromir Pressyanov University of Sofia “St. Kliment Ohridski” Bulgaria

2. CD-method for retrospective 222Rn measurements • Based on radon absorption in the polycarbonate material of CDs/DVDs and etching tracks at certain depth (>76 m) beneath the surface; • Proposed in 2001 and since 2007 regularly applied for practical measurements; • To date: > 1000 measured CDs/DVDs, incl. for retrospective measurements in > 400 dwellings in Bulgaria

3. Key new feature: use of “detectors” that are already available in (almost) any dwelling

4. Etching tracks from absorbed 222Rn: at >76 m beneath the surface.

5. A CD ready for electrochemical etching

6. CDs etching equipment

7. Automatic counting by computer scanner

8. Experimental correlation…

9. Methodology: reliability and precision of the measurements: Background in “new” disks: 2 – 40 cm-2; Problem houses (>200 Bq m-3) can be detected with < 1 y exposure. Possibility for a posteriori individual calibration and temperature correction.

10. Calibration laboratory

11. Influence of: • Pressure: not significant effect (<5%); • Humidity: not significant effect (<7%); • Temperature: bias that can be corrected a posteriori; • Cigarette smoke and dust deposition: not significant effect (<5%); • Plate-out: no contribution to tracks at >80 m (<<1%); • CD/DVD storage in jewel cases: no effect;

12. Useful range of the method (for CDs/DVDs exposed for 10 y):

13. The method is already applied for measurements in: • Air (including retrospective measurements by home stored CDs/DVDs); • Water (including participation in recent intercomparison with USA laboratories); • Soil-gas.

14. What is new in the strategy? • “Traditional surveys”: • To distribute detectors in the targeted group; • To collect and analyze them. The exposure time is well known. • “CD/DVD” based surveys: • Use detectors that are available practically in any dwelling; • To obtain and analyze the disks. To estimate the exposure time.

15. Comparison with conventional measurements in the past

16. CD/DVD-based measuring campaigns in Bulgaria

17. Summary There is a running methodology for CDs/DVDs analysis that is productive (up to 30 disks/day); Uncertainty of a single measurement is within 20%, with <10% achievable; In large scale surveys based on personal communication, >30% of the contacted people can be expected to participate. This percentage is expected to be higher if public information campaigns are organized.

18. New developments (2011)-combined retrospective measurements of radon and thoron

19. The key concept is to measure the net track density (n) in two depths: n (thoron) = n(69 µm) - n(80 µm),where   1.2

20. Combined retrospective measurements of 222Rn and 220Rn Thoron detection window

21. Results – DVDs in jewel cases. Individual a posteriori calibration will be necessary for better precision

22. Practical impact … on radon mitigation strategy House 1: 222Rn = 34 ± 9 Bq m-3 220Rn = 830 ± 400 Bq m-3 House 2: 222Rn = 75 ± 19 Bq m-3 220Rn = 3400 ± 1600 Bq m-3 If these houses are tested with radon detectorsthat are also sensitive to thoron,wrong decision to mitigate against radon can be made, and expenses wasted!!!

23. Thank you …