Calibration factors for LR-115 (type-II) based radon thoron discriminating dosimeter

• Published in: Radiation measurements 2004-02, Vol.38 (1), p.5-17
• Main Authors: Eappen, K.P., Mayya, Y.S.
• Format: Article
• Language: English
• Subjects: Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Geochronology; Isotope geochemistry. Geochronology; LR-115; Pollution, environment geology; Radon; SSNTD; Thoron
• ISSN: 1350-4487; 1879-0925
• DOI: 10.1016/j.radmeas.2003.09.003

Twin chamber solid state nuclear track detector based dosimeters are used for estimating radon ( 222 Rn) , thoron ( 220 Rn) gases and their progeny concentrations in air. These dosimeters employ two numbers of LR-115 (type II) detectors inside each of the two chambers for gas concentration estimations and a third detector is placed externally for progeny measurements. The tracks formed on the detector are etched under specific conditions and counted by spark counting techniques. A theoretical model has been developed to characterize the response of these detectors to alpha particles of different energies incident at different angles on the detector surfaces. This involves the estimation of the total time required for track formation that incorporates both bulk etch rates and the track etch rates. Using this information, the region of influence for the given geometry of the dosimeter is determined. The detectable tracks from this region of influence, computed by the model, are used to obtain the calibration factors (CFs). Results yielded the CF for each of the species in the bare mode exposure as 0.02 tr cm −2 per Bq d m −3 while those for 222 Rn and 220 Rn in the cup dosimeters were estimated as 0.023 and 0.018 tr cm −2 per Bq d m −3 , respectively. The CFs for the cup dosimeters were also determined experimentally in the laboratory by exposing the dosimeters to known concentrations of 222 Rn , 220 Rn and their progeny concentrations. These compared fairly well with the theoretically compounded values. This methodology will be useful in designing cup dosimeters with better efficiencies.