In order to calibrate measurement instruments for radon activity per volume varying over five ord...

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Calibration Device for Radon and Radon Progenies Instrument at NIM

Project Overview

The activity per volume of radon in air can vary over five orders of magnitude from tens of Bq/m3 to several hundred thousands of Bq/m3. Radon and its short-lived progenies account for 50% of the public's exposure to naturally- occurring sources of radiation. It is estimated that they are the cause of about 3% to 14% of all lung cancers, depending on the average radon level in a country. In order to calibrate measurement instruments for activity concentration of Rn-222 and its progenies, a calibration device is being set up: it comprised of a cylindrical type of radon reference chamber (2m3, for radon-222), a walk-in type of chamber (15.5m3, for radon and its progenies) and α and γ measurement systems working as a standard of radon and radon progenies’ activity per volume.


Project Introduction

According to WHO, in many countries, radon is the second most important cause of lung cancer after smoking. The proportion of lung cancers attributable to radon is estimated to range from 3 to 14%. Significant health effects have been seen in uranium miners who are exposed to high levels of radon. The risk of lung cancer increases by 16% per 100 Bq/m3 increase in radon concentration. The dose-response relation is linear – i.e. the risk of lung cancer increases proportionally with increasing radon exposure.

In order to calibrate measurement instruments for radon activity per volume varying over five orders of magnitude, a radon chamber (the figure on left-hand side) has been set up: it covers a volume of 2 m3 for generating reference atmosphere to form a radon radiation field; one high-sensitivity spectrometry type monitor with Si-detector (Durridge Company Model RAD7) and one ionization chamber-type monitor (Genitron Company Model AlphaGuard)to define the specific activity per volume in the reference chamber.

A walk-in type of radon reference chamber(Figure 1) is being set up for radon progenies instrument calibration. It consists of a main exposure chamber, an air-conditioned room and a radon source room. The inner size of the main chamber is 3.1m×2.5m×2.0m. In this chamber, environmental parameters including temperature, humidity, pressure and aerosol size distribution can be independently controlled.

We are moving on to carry out the following study items:

- Developing new accurate techniques for measuring the activity concentration and radon progenies based on absolute methods, such as defined solid angleα-particle counting and TDCR methods.

-Study the correlation of activity concentration of radon and its progenies with environmental parameters obtained (temperature, humidity, pressure and aerosol size distribution).

-Research regulation and control of equilibrium factor F and unattached fraction fp of radon progenies.

 Figure 1. The walk in type radon chamber with inner volume of 15.5 m3 has been built on Oct.,2010 , which will be used for studies of radon and it’s progenies metrology