Presentaci

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On radon surveys design and data interpretation
24th International Conference on Nuclear Tracks
in Solids Bologna, 1-5 Sept 2008
Refreshing Lecture
Lluís Font. Grup de Física de les
Radiacions Universitat Autònoma de Barcelona.
Spain
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On radon surveys design and data interpretation
Two very general comments
Radon has been investigated and monitored in
houses very extensively in the last 30 years.
Read literature to learn from the past and avoid
making the same errors that others did.
My personal view, but more important than my
opinion is to show the students which are the
elements that have to be taken into account when
performing a radon survey.
Bologna, sep 2, 2008
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Contents
On radon surveys design and data interpretation
Goals and scientific interest
Design
Quality assurance
Data analysis
Interpretation of results
Going beyond equilibrium factor thoron,
Bologna, sep 2, 2008
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The goals strongly affect the design of the
survey and data interpretation
Before designing the survey ask yourself
Which are the main goals? Which is the scientific
interest?
Possible/common goals

Bologna, sep 2, 2008
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Survey design
On radon surveys design and data interpretation
Elements of a survey design
Type of dosemeter
Exposure time
Selection of houses. Information to the
inhabitants.
Procedure for installing and collecting the
dosemeters
Bologna, sep 2, 2008
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Survey design
On radon surveys design and data interpretation
If the main goal is to obtain the annual average
of indoor radon levels
Dosimeter type
Exposure time
Selection of houses. Information
Procedure
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Survey design
On radon surveys design and data interpretation
If the main goal is to search for seasonal
variations
Dosimeter type
Exposure time
Selection of houses. Information
Procedure
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Survey design
On radon surveys design and data interpretation
If the main goal is to identify radon prone areas
or houses
Definition of radon prone area. Common approach
area in which a certain percentage of houses
(example 10) exceeds a certain level of annual
radon concentration (example 200 Bqm-3).
Country-specific. Read literature.
Dosimeter type
Exposure time
Selection of houses. Information
Procedure
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Survey design
On radon surveys design and data interpretation
If the main goal is to elaborate a radon risk
map.
Not really well stablished. Under development.
Note difference between a radon map and a radon
risk map (independent on anthropogenic
activities). Read literature.
Dosimeter type
Exposure time
Selection of houses. Information
Procedure
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Survey design
On radon surveys design and data interpretation
If the main goal is to obtain radon exposure of
workers
Under development. A proper estimation of radon
exposure depends strongly on the specific
workplace.
Dosimeter type
Exposure time
Workplaces
Procedure
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Survey design
On radon surveys design and data interpretation
If the main goal is to obtain radon exposure of
workers
Under development. A proper estimation of radon
exposure depends strongly on the specific
workplace. In this example (workplace of Olot,
Spain) the mean radon concentration would clearly
overestimate the radon exposure. Pattern of
occupancy of the workplace is required to a
proper risk assessment.
Fig. taken from Moreno, V., Baixeras, C., Font,
LI., Bach, J. Indoor radon levels and their
dynamics in relation with the geological
characteristics of La Garrotxa, Spain, Radiation
Measurements (2008), doi 10.1016/j.radmeas.2008.0
6.003
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Quality assurance
On radon surveys design and data interpretation
A quality assurance programme is mandatory
Write down a procedure file for each task in your
lab. Task person-independent.
Write down very carefully the instructions to
install the radon detectors and the methodology
used in the survey to distribute/collect the
detectors.
Calibrate your detectors, if possible, in a
well-established radon chamber facility.
You may build up your own radon chamber to check
for time variation of your detector response or
to intercompare the relative response of
different detectors. Check specially for each new
batch of detectors.
Participate in radon intercomparison exercises
periodically.
The traceability of your results is very
important when publishing a paper. Do not use
other calibration factor than that obtained by
yourself in your lab, even if etching conditions
are the same!
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Quality assurance
On radon surveys design and data interpretation
A quality assurance programme is mandatory
Characterise properly your track etch detector
Calibration factor (trcm-2)/(kBqm-3h)
Uncertainty Linear zone
Background track density
Lower detection limit
LD 4.26 ?BG
Currie,Ll. A. 1999. Detection and quantification
limits origins and historical overview..Anal.
Chim. Acta 391, 127-134
Fig. taken from Moreno, et al. Radiation
Measurements (2008), doi 10.1016/j.radmeas.2008.0
6.003
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Data analysis
On radon surveys design and data interpretation
Data analysis
Data normally follows a lognormal distribution.
What does it mean?
The distribution of log of the concentrations
follows a Gaussian curve
Fig. taken from Miles, J. HPA (UK)
Descriptive statistics
Arithmetic Mean (AM) for averaged dose
estimation Geometric Mean GM exp(AM(lnCi)) Geome
tric Standard Deviation GSD exp(SD(lnCi)) Range
Percentage of houses above reference (action)
levels
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Data analysis
On radon surveys design and data interpretation
Data analysis
In any experimental result, provide the
estimation of uncertainty.
See for example ISO Guide for Expression of
Uncertainty in Measurement, October
1993. Guidelines for Evaluating and Expressing
the Uncertainty of NIST Measurement Results. NIST
technical note 1297. 1994 Edition
Report properly your experimental result and its
uncertainty. Remember
The number of significant digits in the
uncertainty cannot be higher than 2.
The number of significant digits in the result
(radon concentration) is given by the
uncertainty. Examples
32528.3 432.7 Bqm-3
128.450 0.67 Bqm-3 450.810 1.20 Bqm-3
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Interpretation of Results
On radon surveys design and data interpretation
Interpretation of results
Be cautious. Before getting a conclusion Did
you check any other explanation to your
findings? Rely on your own results when possible.
Do not be too ambitious. Look for the conclusions
related to the goals of your survey and that can
be demonstrated from your experimental results.
If you use track-etch detectors, you are
measuring the radon exposure. Then you calculate
the mean radon concentration and you may estimate
the radiation dose to which inhabitants have been
exposed.
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Going beyond
On radon surveys design and data interpretation
Going beyond the measurement of radon
Measuring the long-term radon equilibrium factor
with track etch detectors is becoming more an
more popular. It is an old but still interesting
subject. Be careful. Under development (see, for
example Yu et al. Radiat. Meas. 40 (2005)
560-568). Remember the need of calibrating your
dosimeter.
Measuring thoron contribution. Take into account
the short diffusion length. Follow the quality
assurance requirements.
When estimating radiation dose from average radon
concentration, look in detail to the assumptions
made and check if they are reasonable for your
country or area of study. For example normally a
certain indoor occupancy factor is assumed. Is
this value also your case?
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On radon surveys design and data interpretation
THATS ALL, FOLKS!
Thank you very much for your patience!