PTB calibrates radon measuring instruments

The Physikalisch-Technische Bundesanstalt (PTB) has extended its calibration capabilities for measuring instruments intended for use in environmental protection. Since April 1998, instruments for measuring the activity concentration of radon can be calibrated at PTB.

Radon is a radioactive noble gas. It is formed in the ground from uranium, an element which occurs everywhere. A small portion reaches the earth's surface and spreads in the air. Radon and its daughter products formed by radioactive disintegration are inhaled by man. About 40% of the natural radiation to which man is exposed arises from this. In some particular regions, for example regions with granitic subsoil, with mining activities or regions in which certain building materials are used, a radioactivity concentration can develop in houses due to the accumulation effect in buildings, which is significant from the radiation protection viewpoint. For several years, extensive investigations have been carried out in the regions concerned for the purpose of detecting increased radon concentrations in living rooms. It is the aim of these investigations to initiate reconstruction measures, if necessary (according to a recommendation of the Radiation Protection Commission, for example, if the radon concentrations exceed 1000 Bq/m³) to reduce the radon concentration in the buildings concerned. Comparable investigations have been carried out for a fairly long time in other countries, e.g. the USA, Sweden, Great Britain, Austria and Switzerland.

In the past years, the PTB developed facilities for the calibration of radon measuring instruments. Several radon reference chambers have been set up which allow defined radon fields to be adjusted with well-known radon activity values and variable environmental parameters (pressure, temperature, humidity of the air, aerosol content). The radon activity values are selected by use of the PTB's radon gas activity standards. The radon activity values are dissemianted by direct-reading radon measuring instruments serving as working standards. Among the bodies that sponsored the work carried out was the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety which made research funds available.

The facilities set up at PTB allow radon measuring instruments to be calibrated in the measuring range from 100 Bq/m³ to 100 kBq/m³. Uncertainties of measurement between 3,5% and 5% are achieved in the range from 1 kBq/m³ to 100 kBq/m³. These uncertainties are sufficient for measurements carried out in practice. However, for scientific purposes it is of great importance, for methodological reasons alone, to extend the measurement range and to reduce the uncertainty of measurement.
This is the subject of intensive research work carried out at PTB.

Additional information is available from:
Physikalisch-Technische Bundesanstalt
Division of Ionizing Radiation,
Environmental Radioactivity Project
Telephone: 041-531-592-6102
Facsimile: 041-531-592-6109
e-mail: Heinz.Greupner(at)ptb.de