On radon surveys: design and data interpretation

1. 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

2. 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

3. 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

4. Goals and scientific interest On radon surveys: design and data interpretation Publication in a scientific journal To obtain the annual averaged dose and a realistic distribution of radon concentration to which population are exposed. 1 3 To identify radon prone areas or houses. 4 To elaborate a radon risk map 5 6 2 Workplaces: radon levels to which workers are exposed. To set up a certain methodology (to be used in a larger survey) To search for seasonal variations correction factors 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

5. 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

6. Passive. Track-etch detector of closed type. As long as possible! The whole year is the best option. If not possible, two options: i) cover the whole year by consecutive periods or ii) use seasonal correction factors specific for your area of study. Routine surveys in different years. • Survey statistically representative and not biased! • Randomly (for big sampling) • Taking into account census data • 1 in 10000 of the housing stock (UNSCEAR,93) • Information sheet to the inhabitants. Installation/collection in the living room and bedrooms of the houses. Detailed instructions Help of government / local authorities. Minimise looses. 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

7. Passive. Track-etch detector of closed type. Depending on the season duration. Adapted to the specific climate. • Randomly, but other options are acceptable to optimize resources: direct contact with owners, types of (micro)climates. • Information sheet for the collaborators. Installation/collection in the living room and bedrooms of the houses. Detailed instructions Help of government/local authorities. Minimise looses. 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

8. . Any: NTDs, charcoal cannisters, grab sampling, etc. From few hours to several months Short-term may require confirmation • According to any geological, industrial, climate, etc. reason that may suggest the possibility of high radon levels (soil radon data, levels of natural radiation, …) • Information sheet to the inhabitants Installation/collection by trained people. Installation in basements and groundfloors, low-ventilated areas. Confirmation in living rooms and bedrooms. 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 Bq·m-3). Country-specific. Read literature. Dosimeter type Exposure time Selection of houses. Information Procedure

9. . Any: NTDs, charcoal cannisters, grab sampling, etc From few hours to several months Short-term may require confirmation • According to geological / climate factors affecting indoor radon levels (soil radon data, natural radiation levels,…) • Defining a grid (example: 10 km square) • -Information sheet to the inhabitants Installation/collection by trained people. Installation in basements and groundfloors, low-ventilated areas. Confirmation in living rooms and bedrooms. 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

10. . Both time-integrating and time-resolved detectors. Adapted to the working conditions (humidity, aerosol concentration, temperature, …) According to the dosimeter type(s) used • Any in which there are reasonable arguments to suspect a possible significant increase of radiological risk: • -Underground and ground floor (mines, spas,…) • Other sites if located in a radon prone area. Installation/collection by trained people. 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

11. . 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.2008.06.003

12. 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!

13. Quality assurance On radon surveys: design and data interpretation A quality assurance programme is mandatory Characterise properly your track etch detector: Calibration factor (tr·cm-2)/(kBq·m-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.2008.06.003

14. 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)) Geometric Standard Deviation GSD = exp(SD(lnCi)) Range Percentage of houses above reference (action) levels

15. (32.52 ± 0.43) 103 Bq·m-3 128.45 ± 0.67 Bq·m-3 450.8 ± 1.2 Bq·m-3 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 Bq·m-3 128.450 ± 0.67 Bq·m-3 450.810 ± 1.20 Bq·m-3

16. 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.

17. 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?

18. On radon surveys: design and data interpretation THAT’S ALL, FOLKS! Thank you very much for your patience!