STANDARDS, CALIBRATION AND QUALITY ASSURANCE OF RN-222 MEASUREMENTS IN SWEDEN

Inhaled decay products of Rn-222 are the dominant components of the na tural radiation exposure to the general population. Limits have been i ntroduced in Sweden, and recommendations were made in 1980 for decreas ing indoor Rn-222 concentration. The need for the coordinated calibrat ion of measuring instruments as well as for quality assurance was obvi ous for both health and economic reasons. Rn-222 measurements in Swede n are based on standards traceable to the National institute of Standa rd and Technology (NIST) through the use of standard reference materia l Ra-226. Standards for both Rn-222 and short-lived Rn-222 progeny are described together with the reference instrument adopted for these st udies. The calibration of field instruments was performed in a ''radon room'', a climate chamber in which it is possible to vary and monitor the concentration of Rn-222 as well as other characteristics of the i ndoor air such as temperature, humidity, ventilation rate and aerosol concentration. The rules and regulations for field measurements imply a calibration of the instruments yearly, as well as accreditation and training for the companies that carry out the measurements. Examples a re given of the official measurement protocols used for the different types of instruments.