RETROSPECTIVE RADON AND THORON
MEASUREMENTS BY HOME STORED
CDs/DVDs-RESEARCH AND PRACTICE
Dobromir Pressyanov
University of Sofia “St. Kliment Ohridski”
Bulgaria
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
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…
Net track density (cm-2)
600
R2 = 0.998
400
200
0
0
200
400
222
600
800
Rn exposure (kBq d m-3)
1000
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 (<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
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
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”:
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
measurements in the past
CD/DVD-based measuring
campaigns in Bulgaria
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.
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
measurements of 222Rn and 220Rn
Thoron detection window
Results – DVDs in jewel cases. Individual
a posteriori calibration will be necessary
for better precision
Practical impact … on radon
mitigation strategy
House 1:
222Rn
House 2:
222Rn
= 34 ± 9 Bq m-3
220Rn = 830 ± 400 Bq m-3
= 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 …