Laboratory Intercomparison of Passive Radon Detectors

The laboratory intercomparison has been recognised as an important check on the international comparability of radon measurement results and on their quality control procedures.

The Health Protection Agency (formerly the National Radiological Protection Board) has been organising laboratory intercomparisons of passive radon detectors since 1997. All detectors are exposed side by side in the 43 m³ walk-in radon exposure chamber. The chamber contains a ²²²Rn atmosphere which can be varied from around 200 Bq m^-3 to 8000 Bq m^-3. The equilibrium factor F, between radon and its decay products in the chamber, can be altered between 0.1 and 0.9.

In 2010 the facility was fully refurbished and upgraded with a new aerosol generator. The monitoring of the radon concentration inside the chamber was optimised by introducing an Alphaguard ionisation chamber as a second primary instrument. The daily cross-calibration between the Atmos12 DPX and the Alphaguard has shown an excellent agreement. The instruments are calibrated using a radon gas source from Physikalisch-Technischen Bundesanstalt (PTB), Germany.

The next intercomparison of passive radon detectors will be held from 1 September to 31 October 2012 at the Health Protection Agency UK. The detectors will be given five different radon exposures in the range of 50 kBq m^-3 h to 2500 kBq m^-3 h. This will allow the linearity of response of the detectors to be tested over the specified range. Separate arrangements will be made for charcoal detectors.

Laboratories wishing to participate should submit one or more sets of detectors, consisting of the following.

A set of 60 identical etched track detectors (including 10 transit controls)
A set of 30 identical electret detectors (including 5 transit controls)
A set of 15 identical charcoal detectors

Please note that detectors must be sent fully assembled and ready for use.

All detectors should be sent by courier if possible. The cost for each set submitted is £280, which includes the return by courier. If laboratories require detectors to be returned by post they have to note that the detectors should be sent by post. Any delays in delivery of detectors to the originating laboratories shall not affect the schedule.

The HPA divides each set into five groups for exposure to radon, plus a set of transit controls, except in the case of charcoal detectors, which have no transit controls. These exposures are carried out in the HPA radon exposure chamber, at a constant equilibrium factor, for varying lengths of time. Each exposure includes detectors from every set submitted.

After exposure of the detectors, they are returned to the originating laboratories, which are not informed what the exposure conditions were. They are not informed which of their detectors were exposed together, except in the case of charcoal detectors, which have to be returned immediately after each exposure.

Each laboratory estimates the radon exposure given to each detector, including the transit detectors, and reports the results to the HPA blind. Individual reports will be provided by HPA for participants' own detectors shortly after all results have been received by HPA. A fuller, comparative report of all results, identified only by code numbers, will be issued once a detailed analysis of all data and information has been completed.

The new exposure scheme was introduced in 2011 to provide a better measure of the detectors' response across the range of exposures that a laboratory is likely to measure. Also an improved performance parameter was introduced to provide a better evaluation in terms of precision and accuracy with seperate rankings for each exposure level.

Schedule of Intercomparison for 2012

1-30 September	All sets of detectors delviered to the HPA.
1-31 October	Five exposures in the HPA radon chamber.
15 November	Detectors returned to originating laboratories.
31 December	Results and questionnaires returned to the HPA.
31 January	Participants own results reported.
28 February	Draft comparative report distributed to participants by e-mail.
15 March	Comments on draft report returned to the HPA.

 Please note that only results returned by 31 December 2012 will be included in the comparative report.

 If you would like to register your interest please fill in the registration form on this page and send it before 24 September 2012.

 Registration form intercomparison (Word Document, 28 KB)

Enquiries

Dr Zornitza Daraktchieva (Zori.Daraktchieva@hpa.org.uk) or Chris Howarth (chris.howarth@hpa.org.uk)

Radon Dosimetry Team
Dosimetry Services Department
Health Protection Agency
Centre for Radiation, Chemical and Environmental Hazards
Chilton, Didcot, Oxon
OX11 0RQ
UK

Last reviewed: 20 April 2012