Direct Thoron Progeny Sensors Research Articles

Effective dose assessment due to inhalation of 222Rn, 220Rn, and their progeny: highlighting the major contribution of thoron in a thoron-prone area in Cameroon.

To assess public exposure to radon, thoron, and their progeny, measurements were conducted in 50 dwellings within the bauxite-rich area of Fongo-Tongo in western Cameroon. Passive integrating radon-thoron discriminative detectors (specifically RADUET) were employed for radon and thoron measurements. Additionally, concentrations of short-lived radon and thoron progeny were estimated using Direct Radon Progeny Sensors (DRPSs) and Direct Thoron Progeny Sensors (DTPSs) based on LR-115 detectors. The findings revealed indoor radon concentrations ranging from 31 to 123Bqm-3 with a geometric mean (GM) of 62Bqm-3, and indoor thoron concentrations ranging from 36 to 688Bqm-3 with a GM of 242Bqm-3. The Equilibrium Equivalent Radon Concentration (EERC) ranged from 3 to 86Bqm-3 with a GM of 25Bqm-3, while the Equilibrium Equivalent Thoron Concentration (EETC) ranged from 1.2 to 12.5Bqm-3 with a GM of 7.6Bqm-3. Notably, all dwellings recorded radon concentrations below 100Bqm-3. Arithmetic means of radon and thoron equilibrium factors were calculated as 0.47 and 0.04, respectively. To assess annual effective doses from radon and thoron inhalation, equilibrium factors were used along with direct measurements of EERC and EETC. The differences observed in annual effective doses were 4.5% for radon and 42.5% for thoron. Furthermore, the contribution of thoron and its decay products to the annual effective dose from radon, thoron, and their progeny ranged from 12 to 94%, with an average contribution of 58%. Thus, this study found that the effective dose due to thoron inhalation in the study area exceeded that due to radon inhalation. It is concluded that, when evaluating radiation doses and health risks, it is crucial to consider both thoron and its progeny alongside radon and its progeny. This underscores the importance of considering direct measurements for accurately estimating radiation doses.

Application of UV-Visible spectroscopy for measurement of Track density in LR-115 SSNTD based DTPS/DRPS

As measurement of inhalation dose due to radon and thoron progeny is very important in indoor as well as occupational environments, the solid state nuclear track (LR-115) based passive progeny sensors such as Direct Radon Progeny Sensor (DRPS) and Direct Thoron Progeny Sensor (DTPS) are extensively used for this purpose. These detectors need to be chemically etched and spark counted for estimation of track density which is then converted into progeny concentration and finally into inhalation dose using appropriate calibration factors. But for high exposure situations, these detectors have limitations and leads to underestimation of dose. In the present study, we have investigated the possibility of using UV-Visible spectroscopy as an alternative way to estimate the track density in these detectors which can be converted into corresponding progeny concentrations and ultimately to inhalation dose. The transmission spectrum of these progeny sensors under UV-Visible spectrophotometer shows a characteristic peak about wavelength of 380 nm and the variation in transmission at this wavelength was analyzed against the varying alpha exposure. The variation of transmission at 380 nm was observed to be linear with respect to the track density and these linear relations could be used for estimating track density for unknown exposure. This method is a non-destructive alternative way of measuring track density in the DTPS and DRPS and it will be useful for high exposure conditions.

Deposition and spatial variation of thoron decay products in a thoron experimental house using the Direct Thoron Progeny Sensors

Experiments have been carried out using the deposition-based Direct Thoron Progeny Sensors (DTPS) in a thoron experimental house. The objective was to study the thoron decay product characteristics such as the deposition velocities, spatial variability and dependence on aerosol particle concentrations. Since the deposition velocity is an important characteristic in the calibration of the DTPS, it is very important to study its dependence on aerosol concentration in a controlled environment. At low aerosol concentration (1500 particles/cm3) the mean effective deposition velocity was measured to be 0.159 ± 0.045 m h−1; at high aerosol concentration (30 000 particles/cm3) it decreased to 0.079 ± 0.009 m h−1. The deposition velocity for the attached fraction of the thoron decay products did not change with increasing aerosol concentration, showing measurement results of 0.048 ± 0.005 m h−1 and 0.043 ± 0.014 m h−1, respectively. At low particle concentration, the effective deposition velocity showed large scattering within the room at different distances from center. The attached fraction deposition velocity remained uniform at different distances from the wall. The measurements in the thoron experimental house can be used as a sensitivity test of the DTPS in an indoor environment with changing aerosol concentration. The uniform spatial distribution of thoron decay products was confirmed within the experimental house. This indicates that direct measurement of thoron decay product concentration should be carried out instead of inferring it from thoron gas concentration, which is very inhomogeneous within the experimental house.

ESTIMATION OF CONCENTRATION OF RADON, THORON AND THEIR DAUGHTER PRODUCTS IN RESIDENTIAL HOUSES OF SHAHJAHANPUR AND HARDOI

Uranium is a naturally occurring radioactive element present in trace amount throughout the earth's crust. Radon is a progeny of uranium decay series formed from the radioactive decay of radium in the ground water, soil, environment, oil and gas deposits. The lung cancer risk depends on the above recommendation level concentration of radon, thoron and their decay product in the air.The measurement of indoor radon and thoron decay product concentration in houses of Shahjahanpur and Hardoi have been carried out using deposition based direct radon progeny sensors (DRPS) and direct thoron progeny sensors (DTPS) technique. The concentration of radon and thoron is observed to be higher in mud houses as compared to the cemented houses.

Measurement of 222Rn and 220Rn decay product deposition velocities using SSNTD based passive detectors

In the present study, the deposition velocities of 222Rn/220Rn decay products were measured experimentally using SSNTD based passive detectors, direct radon progeny sensor (DRPS) and direct thoron progeny sensor (DTPS) and the results were compared with obtained values by Monte-Carlo simulations. In both cases, deposition velocities were found to be log-normally distributed and also the experimentally measured geometric mean (GM) and geometric standard deviation (GSD) of (0.12, 1.85) m h−1 for radon decay products and (0.07, 1.75) m h−1 for thoron decay products were found to be in good agreement with the simulated values.

Long-term simultaneous measurement of indoor concentration of radon and thoron progeny in the dwellings of Una and Hamirpur District of Himachal Pradesh

Long-term simultaneous measurement of indoor concentration of radon and thoron progeny is made using passive alpha track detectors in the dwellings of Una and Hamirpur district of Himachal Pradesh. The preliminary results of these measurements are reported, particularly regarding direct thoron progeny sensor (DTPS) and direct radon progeny sensor (DRPS) being set up in real field conditions for the first time in Himachal Pradesh. The concentrations of radon and thoron progenies (equilibrium equivalent radon and thoron concentration (EERC/EETC)) were measured for all the seasons of the year. A remarkable finding is the positive correlation between EERC and EETC (R2 = 0.79 in summer and R2 = 0.81 in winter). A comparison was made with the measurements of EERC/EETC in summer and winter season. The ratio of EETC/EERC was calculated and this agrees with worldwide range. This study contributes to the status of Himachal Pradesh in the mapping of radon in India.

Multi-parametric approach towards the assessment of radon and thoron progeny exposures

Conventionally, the dosimetry is carried out using radon and thoron gas concentration measurements and doses have been assigned using assumed equilibrium factors for the progeny species, which is inadequate pertaining to the variations in equilibrium factors and possibly due to significant thoron. In fact, since the true exposures depend upon the intricate mechanisms of progeny deposition in the lung, therefore an integrated approach for the assessment of progeny is essential. In this context, the recently developed deposition based progeny concentration measurement techniques (DTPS: Direct Thoron progeny sensors and DRPS: Direct Radon progeny sensors) appear to be best suited for radiological risk assessments both among occupational workers and general study populations. DTPS and DRPS consist of aluminized mylar mounted LR115 type passive detectors, which essentially detects the alpha particles emitted from the deposited progeny atoms on the detector surface. It gives direct measure of progeny activity concentrations in air. DTPS has a lower limit of detection limit of 0.1 Bq/m(3) whereas that for DRPS is 1 Bq/m(3), hence are perfectly suitable for indoor environments. These DTPS and DRPS can be capped with 200-mesh type wire-screen to measure the coarse fraction of the progeny concentration and the corresponding coarse fraction deposition velocities as well as the time integrated fine fraction. DTPS and DRPS can also be lodged in an integrated sampler wherein the wire-mesh and filter-paper are arranged in an array in flow-mode, to measure the fine and coarse fraction concentration separately and simultaneously. The details are further discussed in the paper.

An integrated approach for the assessment of the thoron progeny exposures using direct thoron progeny sensors

Assessing the risks due to thoron and its progeny is of considerable importance in the public domain and in operations related to the thorium fuel cycle. Deposition-based progeny concentration measurement techniques (direct thoron progeny sensors, DTPSs) appear to be best suited for radiological risk assessments among both occupational workers and general populations. The DTPSs lodged in wire-mesh and filter paper-integrated sampler and operated in flow mode can be used to measure the unattached and attached fractions. The wire-mesh-capped DTPS system can be used to measure the deposition velocity of the unattached and attached fractions separately. In the present work, the DTPSs in different modes have been described and the experiments for measuring the multiple parameters related to the indoor thoron progeny are presented.

Response of direct thoron progeny sensors (DTPS) to various aerosol concentrations and ventilation rates

Direct thoron/radon progeny sensors (DTPS/DRPS) are absorber mounted LR115 type track detectors for measuring the time-averaged progeny concentrations. Through a large number of experiments, the sensitivity factor of these sensors in natural indoor environment was found to be nearly constant at a value of 0.94 Tr cm−2 d−1/EETC (Bq m−3) for DTPS and 0.09 Tr cm−2 d−1/EERC (Bq m−3) for DRPS. The constancy of the sensitivity factor in the natural environments is attributed primarily to the presence of large aerosol concentrations and relatively low ventilation rates in time-averaged measurements. However, detailed model calculations suggest that in extreme scenario i.e. at high ventilation rate and low aerosol concentrations, the sensitivity factor can be quite different. Such situations are likely to occur in occupational plant areas. Therefore systematic chamber experiments were carried out to using DTPS, to estimate the variability of the sensitivity factor in these extreme conditions. In the first set, the sensitivity factor of DTPS was measured in 6 different aerosol concentrations at zero ventilation rates. The sensitivity factor showed a steep decrease as the aerosol concentration increased to about 8554 particle cm−3, after which it remained almost constant with increase in aerosol concentration. The second set of experiments was conducted at ∼5000 particles cm−3 at three different ventilation rates. The sensitivity factor was found to increase with increase in ventilation rate. The results are further discussed.

Measurement of 220Rn/ 222Rn progeny deposition velocities on surfaces and their comparison with theoretical models

The deposition velocities of 222Rn (radon) and 220Rn (thoron) progeny species have been measured in a chamber, in a test house, and in dwellings by relating the atom deposition fluxes of these species to their atom concentrations in air. These measurements were carried out using absorber-mounted nuclear track detectors (LR-115) which selectively register the tracks due to alpha emissions from 212Po and 214Po from the deposited atoms of 220Rn and 222Rn progeny species, respectively. These are termed as DRPS (direct radon progeny sensor) and DTPS (direct thoron progeny sensor). Measurement of parameters such as ventilation rate, particle size distribution and unattached fractions were also carried out along with deposition velocity. The experimental data on deposition velocity in test house and chamber were compared with the predictions based on the indoor progeny dynamics model and particle deposition models. These showed excellent agreement with experimental values although the data on radon progeny showed slightly higher dispersion. The progeny deposition velocities were also measured in living rooms of dwellings in Mumbai and were found to be close to the model results which in turn imply that in the long term, the average environmental conditions are similar to that in the test house. These results point at a plausible constancy of long time averaged indoor deposition velocities. From these studies, we are inclined to assign summary values of deposition velocities of 0.075 m h −1 for 220Rn progeny and 0.132 m h −1 for 222Rn progeny, for indoor conditions.

Study of a deposition-based direct thoron progeny sensor (DTPS) technique for estimating equilibrium equivalent thoron concentration (EETC) in indoor environment

A study has been carried out to examine the suitability of a passive, deposition-based technique for estimating the time-integrated equilibrium equivalent thoron concentration (EETC) in indoor environment using a direct thoron progeny sensor (DTPS). DTPS is an absorber-mounted LR-115-type nuclear track detector tuned to respond only to the 8.78 MeV alpha particles emitted from the deposited activity of 212Po on the absorber surface. The study has been carried out in two steps, the first step comprising the estimation of track registration efficiency ( η ) and the second step comprising the estimation of effective deposition velocity of thoron progeny aerosols on the detector surface in natural and laboratory environments. The track registration efficiency is found to be 8.3% for 212Po and less than 0.02% for all other alpha emitters including 222Rn (radon) progeny, thereby enabling a precise discrimination of thoron progeny. The deposition velocity of thoron progeny aerosols on DTPS surface has been measured in conjunction with active air sampling techniques for different orientations of the deposition surface. The geometric mean deposition velocity was found to be 0.077 m h - 1 having a narrow spread (geometric standard deviation of 1.35). Upon combining these factors, the overall sensitivity factor is estimated to be 0.94 Tr cm - 2 d - 1 / EETC ( Bq m - 3 ) , which indicates ∼ 45 times higher sensitivity as compared with conventional bare detector techniques (which register alpha particles emitted directly from air). The results obtained have been compared with currently used aerosol deposition models and progeny equilibrium models by using the aerosol number size and progeny activity distributions measured with scanning mobility particle sizer (SMPS) and low-pressure cascade impactor, respectively. The results are in good agreement with each other. A sensitivity analysis of the response characteristics of DTPS with respect to room ventilation rate and aerosol concentrations has been carried out to assess the variability of the sensitivity factor in the context of indoor dosimetry. The results are further discussed.