RETROSPECTIVE RADON AND THORON MEASUREMENTS BY HOME STORED CDs/DVDs-RESEARCH AND PRACTICE Dobromir Pressyanov Dobromir Pressyanov University of Sofia “St. Kliment University of Sofia “St. Kliment Ohridski” Ohridski” Bulgaria Bulgaria
Feb 06, 2016
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 …