RETROSPECTIVE RADON AND THORON MEASUREMENTS BY HOME STORED CDs/DVDs-RESEARCH AND PRACTICE Dobromir PressyanovUniversity of Sofia St. Kliment OhridskiBulgaria

CD-method for retrospective 222Rn measurementsBased 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

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

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

A CD ready for electrochemical etching

CDs etching equipment

Automatic counting by computer scanner

Experimental correlation

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.

Calibration laboratory

Influence of: Pressure: not significant effect (

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

DetectorMDA(Bq m-3)Saturation level (corresponding to 4000 cm-2)(Bq m-3)CDs at 83 m2.93000CDs at 117 m4.04100

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.

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.

Comparison with conventional measurements in the past

CD/DVD-based measuring campaigns in Bulgaria

SummaryThere 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 30% of the contacted people can be expected to participate. This percentage is expected to be higher if public information campaigns are organized.

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

The key concept is to measure the net track density (n) in two depths:

n (thoron) = n(69 m) - n(80 m), where 1.2

Combined retrospective measurements of 222Rn and 220RnThoron detection window

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

Practical impact on radon mitigation strategyHouse 1:222Rn = 34 9 Bq m-3220Rn = 830 400 Bq m-3

House 2:222Rn = 75 19 Bq m-3220Rn = 3400 1600 Bq m-3

If these houses are tested with radon detectors that are also sensitive to thoron, wrong decision to mitigate against radon can be made, and expenses wasted!!!

Thank you