RETROSPECTIVE RADON AND THORON MEASUREMENTS BY HOME STORED

CDs/DVDs-RESEARCH AND PRACTICE

Dobromir PressyanovDobromir Pressyanov

University of Sofia “St. Kliment Ohridski”University of Sofia “St. Kliment Ohridski”

BulgariaBulgaria

CD-method for retrospective CD-method for retrospective 222222Rn measurementsRn 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

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

dwelling

Etching tracks from absorbed Etching tracks from absorbed 222222Rn: at Rn: at >76 >76 m beneath the surface.m beneath the surface.

A CD ready for electrochemical A CD ready for electrochemical etchingetching

CDs etching equipmentCDs etching equipment

Automatic counting by computer Automatic counting by computer scannerscanner

Experimental correlation…Experimental correlation…

R2 = 0.998

0

200

400

600

0 200 400 600 800 1000

222Rn exposure (kBq d m-3)

Ne

t tr

ac

k d

en

sit

y (

cm

-2)

Methodology: reliability and Methodology: reliability and precision of the measurements: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 laboratoryCalibration laboratory

Influence of: 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;

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

Detector MDA(Bq m-3)

Saturation level (corresponding to 4000

cm-2)(Bq m-3)

CDs at 83 µm 2.9 3000

CDs at 117 µm 4.0 4100

The method is already applied for The method is already applied for measurements in: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?What is new in the strategy?

• “Traditional surveys”:

1) To distribute detectors in the targeted group;

2) To collect and analyze them. The exposure time is well known.

• “CD/DVD” based surveys:

1) Use detectors that are available practically in any dwelling;

2) To obtain and analyze the disks. To estimate the exposure time.

Comparison with conventional Comparison with conventional measurements in the pastmeasurements in the past

CD/DVD-based measuring CD/DVD-based measuring campaigns in Bulgariacampaigns in Bulgaria

SummarySummary

• 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.

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 µm) - n(80 µm),where 1.2

Combined retrospective Combined retrospective measurements of measurements of 222Rn and Rn and 220RnRn

Thoron detection window

Results – DVDs in jewel cases. Individual Results – DVDs in jewel cases. Individual a posterioria posteriori calibration will be necessary calibration will be necessary

for better precisionfor better precision

Practical impact … on radon Practical impact … on radon mitigation strategymitigation 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 detectors that are

also sensitive to thoron, wrong decision to mitigate

against radon can be made, and expenses wasted!!!

Thank you …