November 29th, 2007 - h. 15:00

Seminar Room (A-34)

R. Mishra
(Bhabha Atomic Research Centre, India)

Development of direct 220Rn/222Rn progeny sensors based on LR115 track detectors


To well assess the radiation exposure of the public in private homes and in workplaces, the information about the airborne concentration of the alpha-emitter progeny of 222Rn and 220Rn (218Po and 214Po in the case of 222Rn, and 216Po, 212Bi and 212Po in the case of 220Rn) is of great interest.

The reason is that the progeny contribute a large fraction to the background radiation dose by inhalation route. Direct estimation of decay product concentration using passive track detectors has been one of the major challenges in this field. To this end Direct Thoron Progeny Sensor (DTPS) and Direct Radon Progeny Sensor (DRPS) are developed which are basically deposition based absorber techniques based on LR115 track detectors.

The property of the progeny atoms to plateout on material surfaces is effectively utilized for obtaining the progeny deposition velocity, which is compared with the model calculations. Progeny deposition velocity along with the track registration efficiency of the sensors are used for determining the sensitivity factor which represents the tracks expected per unit EECT and EECR (Equilibrium Equivalent Thoron Concentration and Equilibrium Equivalent Radon Concentration respectively) for DTPS/DRPS.

These sensors are developed to operate in two modes: i) Bare-mode based on the natural deposition technique, intended to be used for personal dosimetry in uranium mines and thorium processing industries; ii) Flow-mode which is independent of the environmental factors can be used as reference progeny sampler for periodic calibration of the progeny sensors. Both the modes are standardized and field-studies are under progress.

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RB, 16/11/07