The aim of work package 2 is to investigate and to reduce the influence of thoron (220Rn) and its progeny on radon (222Rn) end-user measurements and radon calibrations. An influence of thoron on the radon activity concentration measurements has already been observed with some radon monitors and special care of that problem is needed. In particular, this influence, if not properly corrected, can introduce bias in the radon risk estimates or can generate false alarms if the detectors are used to identify dwellings with radon concentrations that exceed reference/action levels. Both thoron and its progeny (212Pb, 212Bi+212Po/208Tl) should be taken into account, as the generated thoron progeny can remain within the detector volume long after the decay of the parent thoron atoms. As the possible thoron influence should be taken into account in the calibrations of the detectors/apparatus, a large sample group of end-users instruments will be investigated for thoron influence on the radon results. This influence will be studied experimentally under pure thoron and mixed radon + thoron concentrations and at different temperature conditions that are typical for the environment. The properties of different filters/foils/membranes to serve as efficient barriers for thoron, not reducing radon permeability significantly, will be investigated in order to propose methods for reduction of thoron influence on the radon measurements
Task 2.1: Organization and execution of a consortium exercise to ensure traceability of the secondary reference instruments used in the experimental research to the primary thoron system at IRSN, Saclay, France.