The ENEA-IRP thoron calibration facility.

To check the consistency of a (220)Rn measurement, performed by passive alpha track detector (ATD), the use of an accurate (220)Rn exposure calibration facility is mandatory. The ENEA Radon Service developed a new CR-39 ATD-Tn, coupled to the radon ATD-Rn and, to assess its sensitivity, had to design a small calibration facility, which has been recently modified to improve the spatial homogeneity exposure conditions inside the chamber, to get a continuous monitoring of the (220)Rn concentration and to reduce radon contamination. A better knowledge of the circuit response allowed selecting the best-operating conditions and how to regulate the thoron concentration. The active thoron monitor has been changed to serve as a continuous sampling and measuring device rather than a grab one; particular care has been devoted to assess the (216)Po losses on the device's inner surfaces and to evaluate the chamber transit time correction factor.

How to assess the sensitivity and related uncertainty of a new solid state passive thoron measuring device.

To test the sensitivity of our CR-39 alpha-track detector thoron passive device (ATD-TnPD), a closed-circuit exposure facility, composed by a new thoron source, a small exposure chamber and a new absolute (220)Rn active monitor (TnM), was set up. (220)Rn exposure was evaluated by assessing the TnM response and its combined uncertainty. The ATD-TnPD's sensitivity was determined by three thoron exposures, tested at different etching times. A non-linear relationship on etching conditions was obtained, with values in the range 1.54-1.76 (tracks cm(2))(kBq h m(-3))(-1).

Meeting new challenges in radon measurements service with solid state alpha track analysis.

The national and international radioprotection legislation now covers exposures to the naturally occurring radioactive materials (NORM) with particular emphasis on radon in workplaces. Consequently, a number of working environments have now been brought into the realm of radiation protection monitoring with a corresponding increase in the demand for radon monitoring services. The new challenges occasioned by the increase in demands are illustrated in this paper together with the radon measurement system developed at the ENEA IRP radon Service. In particular, this paper emphasises how to control using hardware and software analysis, the distributions (diameters and areas) of the track shape, which directly affect the quality of the radon service.