[en] Solid State Nuclear Track Detector (SSNTD) based diffusion chambers have been widely used for residential radon measurements due to their cost effectiveness, portability and easy-to-use feature. In India, an LR-115 track detector based twin-cup dosimeter has been in use for about a decade for indoor ²²²Rn and ²²⁰Rn measurements. However, the estimation of the gas concentrations using this dosimeter was based on the assumption of the same entry rate of the gases into the two cups of the dosimeter, which may not be valid for dosimeters deployed in turbulent environmental conditions. To overcome this limitation, a new pin-hole based ²²²Rn/²²⁰Rn discriminating measurement device has been developed. The underlying discrimination technique has been established by modelling ²²²Rn and ²²⁰Rn diffusion into a pin-hole chamber and validating the same by carrying out experiments in a test chamber. The device has been calibrated at Bhabha Atomic Research Centre, Mumbai following the standard procedures to correlate the number of tracks registered in the LR-115 detector placed in the two chambers to the ²²²Rn and ²²⁰Rn concentration in the environment. Salient features of the device include (i) the pin-holes act as ²²²Rn/²²⁰Rn discriminator and eliminate the requirement of membrane filter used in the earlier twin cup design (ii) the single entrance design for gas transmission and (iii) use of multiple pin-holes of reasonably small radius minimises effect of turbulence on ²²²Rn/²²⁰Rn transmission factors so that the calibration factor is independent of indoor turbulence. - Highlights: • A model is developed to discriminate ²²²Rn and ²²⁰Rn using pin-hole. • Model is validated against the experimental results. • A new pinhole discriminated ²²²Rn/²²⁰Rn passive measurement device is developed. • The new device overcomes the limitation of the conventional twin cup dosimeter. • Device is calibrated using standard sources of ²²²Rn and ²²⁰Rn

[en] In recognition of the fact that building materials are an important source of indoor radon, second only to soil, surface radon exhalation fluxes have been extensively measured from the samples of these materials. Based on this flux data, several researchers have attempted to predict the inhalation dose attributable to radon emitted from walls and ceilings made up of these materials. However, an important aspect not considered in this methodology is the enhancement of the radon flux from the wall or the ceiling constructed using the same building material. This enhancement occurs mainly because of the change in the radon diffusion process from the former to the latter configuration. To predict the true radon flux from the wall based on the flux data of building material samples, we now propose a semi-empirical model involving radon diffusion length and the physical dimensions of the samples as well as wall thickness as other input parameters. This model has been established by statistically fitting the ratio of the solution to radon diffusion equations for the cases of three-dimensional cuboidal shaped building materials (such as brick, concrete block) and one dimensional wall system to a simple mathematical function. The model predictions have been validated against the measurements made at a new construction site. This model provides an alternative tool (substitute to conventional 1-D model) to estimate radon flux from a wall without relying on ²²⁶Ra content, radon emanation factor and bulk density of the samples. Moreover, it may be very useful in the context of developing building codes for radon regulation in new buildings. - Research highlights: → A model is proposed to predict radon flux from wall using flux of building material. → It is established based on the diffusion mechanism in building material and wall. → Study showed a large difference in radon flux from building material and wall. → Model has been validated against the measurements made at a new construction site. → Model leads to correct interpretation of building material flux with indoor radon.

[en] The release of "2"2"0Rn gas (conventionally referred to as thoron) is an issue of concern from the radiological point of view for occupational environments pertaining to the thorium fuel cycle. Studies for understanding its release and developing systems to control it are crucial for exposure control research. A thorough study of the “Delay Volume Technique” for mitigation of "2"2"0Rn has been carried out. Experiments have been carried out with "2"2"0Rn source and associated measurement system in a cubical chamber (delay chamber) of 0.5 m"3 volume. For different flow conditions and inlet-outlet positions, "2"2"0Rn transmission factor has been obtained. Computational Fluid Dynamics (CFD) technique has been employed for these experimental conditions and the simulated transmission factors have been compared. The results show that the flow and the position of the inlet and outlet play an imperative role in the transportation, mixing and subsequent mitigation of thoron inside the chamber. Predictive capability of CFD technique for such delay volume experiments has been validated in this work. A comparison has been made with uniform mixing model and it is found that the results of simulation differ appreciably from that of uniform mixing model at the tested flow regime. - Highlights: • Simulation has been performed for finding thoron transmission through a delay chamber. • Validation has been done against experimental observations. • Study explores the changes in transmission factor due to changes in air flow and inlet-outlet position. • The limiting capability of uniform mixing models for thoron transmission has been noted

[en] Paper presents an empirical formula for estimation of radon exhalation rate from building surfaces like wall, ceiling and flooring based on the radon exhalation rate measured from the building materials (e.g. brick, concrete block, tile etc.). The empirical formula used needs basic input parameters of radon exhalation rate from a building block and diffusion length of the material. Since quickest technique (radon growth curve analysis) are available to find out the radon exhalation rate from the building material, this formula will be useful for a quick assessment of indoor radon concentration in a room. This approach will also help in designing a room in high radon prone area with choice of building materials to be used for the construction of wall, flooring or ceiling with suitable thickness and adequate ventilation to keep the indoor radon level below the prescribed action level. (author)

[en] Environmental systems are so complex that the presumption that we can have a full understanding of the system impacts and predict the risk may not be easy even with extended measurement. But developments in instrumental methods/techniques have provided the strong tool for early understanding of the levels at which the contaminants are present in the environment and the impacts if any at that level. It definitely helps us to regulate the level of the agents or minimize the action that is causing the problem. While regulatory control is essential, it is the supportive concentration based cause effect relationship which are to be provided by the scientific community

[en] Online radon and thoron monitors have been developed using ZnS(Ag) detector for continuous monitoring of concentrations in occupational and general environments. Their performance has been tested successfully both in laboratory and field conditions. Special features of these monitors include low cost, high sensitivity and non-interference of humidity and trace gases. The capability of these radon monitors for networked radon monitoring in U mines and in the U-tailings pond has been demonstrated. The thoron monitor is designed for stack monitoring of thoron release in a thorium processing facility. Being highly sensitive, these monitors can also be used for radon/thoron monitoring in dwellings, radon exhalation measurements, radon concentration in water samples and thoron emission measurements from monazite sands in High Background Radiation Areas. (author)

[en] Charcoal based canisters are highly recommended passive detectors for short term measurements of ²²²Rn gas concentrations. Sorption properties of charcoal make it ideal for ²²²Rn adsorption and holding. These detectors needs to be calibrated under different environmental conditions (varying relative humidity, temperature, ²²²Rn concentration, etc.) before their deployment for actual ²²²Rn measurements, as their adsorption properties are known to be sensitive to these parameters. In this paper, we demonstrate the estimation of calibration factor and evaluation of the performance of the activated charcoal based ²²²Rn adsorption detectors by exposing them in the ²²²Rn chamber

[en] This paper presents the extent of thoron (²²⁰Rn) interference in the radon (²²²Rn) exhalation rate, measured by solid state nuclear track detector based 'Can' technique. Experiments were carried out following the standard procedure of 'Can' technique as well as active technique as a reference method for ²²²Rn and ²²⁰Rn exhalation measurements. It was found that ²²⁰Rn interference may lead to overestimation of ²²²Rn exhalation by a significant factor which can be as high as 12 depending upon the rate of ²²⁰Rn exhalation from samples. (author)

[en] Radon, produced by radioactive decay of the trace amounts of uranium present in most rock is considered as a natural tracer for uranium exploration and studying earthquake precursory phenomena such as changes of radon concentration due to stress release from earth crust. Radon emitted from rocks containing uranium can partly dissolve and remain in ground water, subject to radioactive decay, until dispensed and aerated. Hence, a measurement of dissolved radon in ground water is a key path finder for uranium deposit. The paper discusses formulation and modeling of radon transport in soil media and its usefulness for interpretation of measured radon data with uranium deposit and stress release from earth crust. Analytical models were derived from basis radon transport theory of porous media considering diffusion as well as advection transport in addition to radon emanation and radioactive decay in the soil pore. Analysis of the model solutions indicates that radon monitoring in sub-soil is more reliable for stress release and earthquake precursory studies than deep soil sampling. On the other hand, radon monitoring in deep soil, preferably in ground water, can be applied for detecting the uranium deposit in certain areas. But it is necessary to measure "2"2"6Ra along with radon to compensate the contribution of radon from dissolved "2"2"6Ra in the water. The compensated radon activity is the actual indicator of "2"2"6Ra and uranium content in rocks at the vicinity of ground water source. Results of two experimental case studies were also presented to validate the above prediction of model. (author)

[en] This study presents a new method that has been developed for the correct estimation of thoron emanation coefficient from powders or sands with considerably high ²²⁴Ra content. The technique utilizes a closed loop setup in which thoron emitted from a thin layer of sample in the 'powder sandwich' (PS) is measured using suitable thoron detector and the mass exhalation rate is determined. The powder sandwich is prepared by carefully placing a known mass (M) of source powder, about 100 mg, between two glass fiber filter papers. This arrangement is sealed at edges using adhesive, to avoid any spillage or loss of the powder. The powder sandwich arrangement ensures that the thickness of thoron sample is much less than the thoron diffusion length, allowing all the thoron gas produced to come out through the filter paper. The powder sandwich made as above is then placed in a closed loop containing a thoron detector and a pump. When the pump is turned on, it circulates the air in the closed loop causing all the thoron gas formed in the powder sandwich to come out. Within few minutes, the thoron concentration in the closed loop reaches an equilibrium value. This thoron concentration is measured using a thoron detector