Laboratory facility to create reference radon + thoron atmosphere under dynamic exposure conditions

The sensitivity of innovative techniques for measuring low levels of radon in the environment using passive detectors

In recent years, there has been a significant surge in interest in measuring low radon levels in the environment. These measurements are valuable, particularly for identifying radon priority areas as required by the European Council Directive 2013/59/EURATOM and for research related to climate change. Due to the limited sensitivity of existing radon detectors/monitors in addressing these challenges, substantial efforts have been devoted to developing new designs. This report compares the sensitivity of several innovative designs with that of existing passive radon monitors. These novel designs incorporate alpha track detectors, including large area low background detectors, with activated carbon fabric used as an efficient radon adsorber/radiator. Recent innovative solutions to mitigate the impact of temperature and humidity on detectors using adsorbers are also discussed. The background signal of detectors intended for use in these novel designs is examined, and their sensitivity is evaluated. The findings demonstrate that these novel designs have the potential to significantly enhance the sensitivity of long-term radon measurements, surpassing the detectors currently in widespread use by more than an order of magnitude.

New generation of highly sensitive radon detectors based on activated carbon with compensated temperature dependence

Recently patented compensation module for sensors of radioactive noble gases paves the way for novel designs of radon detectors/monitors with adsorbents, suitable for long-term measurements. The module compensates the strong influence of the temperature on the response of detectors with activated carbon or other ad/absorbents. This report describes radon detectors in which activated carbon fabric is coupled with a solid state nuclear track detector and placed in a compensation module. The module is a hermetic volume made of polyethylene foil, through which the radon diffuses. Two reciprocal trends make possible the temperature compensation: that of the radon penetration through the walls, which increases with the increase of the temperature, and that of the adsorption, which decreases. The results show that outside the module the variation of the detector response over the range of 5-35 °C is 230-305%. In contrast, inside the module the variation is reduced to 6-17%. The module also protects the sensor from humidity and thoron, keeping its sensitivity to radon 7-9 times higher than that of commonly used radon detectors. This makes the new detectors very useful for measurement of low radon concentrations in the atmosphere.

Approaches for reduction of the temperature bias on radon detectors packed in anti-thoron polymer membranes

Passive and active detectors used for radon (²²²Rn) measurements can be influenced by thoron (²²⁰Rn). Polyethylene membranes are very appropriate diffusion barriers for anti-thoron protection of such detectors. However, if not properly chosen, these membranes may not reduce efficiently the thoron influence or could introduce temperature bias in the radon sensitivity of the detectors. In this work three approaches are proposed dealing with the thoron influence and the temperature bias introduced by packing in polymer membranes. The approaches exploit a model of the radon and thoron diffusion transport through the membranes and the already known diffusion properties of the membranes to estimate the thoron influence and the temperature bias and to take them into account. The approaches are experimentally verified. It is shown that, in some cases, with the proper choice of membrane the thoron influence could be reduced down to few percents introducing only a few percents temperature bias. Additionally, in the cases when temperature bias is significant and cannot be avoided (the thoron bias in that cases is shown to be below 1%), the proposed approaches allow to estimate and to correct that bias.

Regulation and control methods for the unattached fraction of 220Rn progeny in a 220Rn progeny chamber

The unattached fraction of ²²⁰Rn progeny is one of the key parameters in lung dose evaluation models. To study the behavior of unattached ²²⁰Rn progeny and to prepare for calibration of the unattached ²²⁰Rn progeny monitors, a ²²⁰Rn progeny chamber that could stably regulate different unattached fractions of ²²⁰Rn progeny was established. A recirculation loop to eliminate the effects of the sampling and a loop connected to the dilution chamber to supplement the carrier aerosol were set up. Also, a theoretical model regarding the regulation of the unattached fraction of ²²⁰Rn progeny was established. Continuous measurements of the unattached fraction were conducted using the combination of a single-layer wire screen and a filter membrane. The experimental results showed that, under different aerosol levels, the relative standard deviation (RSD) of ²¹²Pb concentration during the continuous samplings was within 10.7% and the RSD of the unattached fraction of ²¹²Pb was within 9.9%. The relative deviation between the theoretical and the experimental values of ²¹²Pb concentration was within 16.7% and the model calculation values of the unattached fraction of ²¹²Pb were consistent with measured results.

Partition Coefficients and Diffusion Lengths of 222Rn in Some Polymers at Different Temperatures

In this work, the partition coefficients K and diffusion lengths LD of radon in some polymers are experimentally determined for several temperatures in the range T = 5–31 °C. Some of the obtained values are compared to published data available for the given temperatures. It is shown that the temperature dependencies of the partition coefficients K(T), the diffusion lengths LD(T), and the permeabilities P(T) could be described analytically for the studied temperature range 5–31 °C. This allows estimation of these quantities in the given temperature range and quantitative description of the transport of radon in the studied polymers.

Testing and Calibration of CDs as Radon Detectors at Highly Variable Radon Concentrations and Temperatures

The application of the compact disk (CD) method for radon measurements at mines, caves and other workplaces needs testing under highly variable exposure conditions. We present the results from a blind comparison of CDs exposed in the Laboratory of Natural Radiation (Saelices el Chico, Spain). During the exposure the temperature varied from 6.5 to 24.9 °C (average 12.6 °C) and the ²²²Rn activity concentrations varied from <10 Bq m⁻³ to 147 kBq m⁻³. Good correspondence was observed between the integrated ²²²Rn activity concentration determined by the reference instruments in the laboratory (122,500 ± 6100 kBq h m⁻³) and that assessed by analysis of the CDs at a depth 80 µm beneath the front surface (118,000 ± 12,000 kBq h m⁻³) and at a depth of 120 µm (106,000 ± 12,000 kBq h m⁻³). The theoretical modeling of the CD response under variable temperature and radon concentration suggested that the small bias is probably due to the time variation of the calibration factor because of the time variations of the temperature.

Identifying radon priority areas and dwellings with radon exceedances in Bulgaria using stored CD/DVDs

The implementation of the 2013/59/EURATOM directive in the part related to radon exposure imposes challenges for radon measurement methodology and radon survey design. Among them is the need to have estimates (preferably direct) of the annual average radon concentrations, which can be directly compared to the recommended reference levels. On this basis, the surveys should make possible the identification of dwellings with indoor radon above the reference levels and "radon priority areas" where significant proportion of the dwellings falls in this category. The performance of the CD/DVD method for radon measurements as a tool to address these issues is presented. A recent large scale field study based on the CD/DVD method that was carried out in the suburb area of Sofia, Bulgaria is described. Part of the studied area was affected in the past by the uranium mining and milling industry. In total 462 disks (CDs and DVDs) taken from 335 private dwellings from 10 districts in the region were analyzed. The results revealed the large heterogeneity in radon distribution in the area, with the percentage of dwellings with a ²²²Rn level above 300 Bq m^-3 ranking from about 7% to 74%. The district of Yana, for which this percent was 74, was identified as the area of highest radon priority in the region. The paper also discusses how prompt identification of dwellings with radon above the reference level by CD/DVDs can be incorporated within an integrated approach to the radon problem. Within this approach the radon hazard is identified shortly after the stakeholder's decision to test, which allows fast solution of the problem without waiting the long (and usually demotivating) one-year period needed for direct results by the commonly used prospective methods.

THE CD/DVD METHOD AS A TOOL FOR THE HEALTH PHYSICS SERVICE AND VENTILATION DIAGNOSTICS IN UNDERGROUND MINES

The CD/DVDs used as radon (222Rn) and thoron (220Rn) detectors can provide a sufficiently sensitive and cost-efficient option for passive radiation monitoring in underground mines. This note presents results of measurements made under real environmental conditions by CD/DVDs. Comparison with conventional diffusion chambers was made and good correspondence was observed. Correlation between 222Rn and 220Rn was studied by CD/DVDs and no signs for any correlation were observed. Dedicated study in a mine gallery showed that CD/DVDs can be successfully used for the purposes of ventilation diagnostics by identifying sources of air contaminated with radon.

Controlling 212Bi to 212Pb activity concentration ratio in thoron chambers

It is necessary to establish a reference atmosphere in a thoron chamber containing various ratios of ²¹²Bi to ²¹²Pb activity concentrations (C(²¹²Bi)/C(²¹²Pb)) to simulate typical environmental conditions (e.g., indoor or underground atmospheres). In this study, a novel method was developed for establishing and controlling C(²¹²Bi)/C(²¹²Pb) in a thoron chamber system based on an aging chamber and air recirculation loops which alter the ventilation rate. The effects of main factors on the C(²¹²Bi)/C(²¹²Pb) were explored, and a steady-state theoretical model was derived to calculate the ratio. The results show that the C(²¹²Bi)/C(²¹²Pb) inside the chamber is mainly dependent on ventilation rate. Ratios ranging from 0.33 to 0.83 are available under various ventilation. The stability coefficient of the ratios is better than 7%. The experimental results are close to the theoretical calculated results, which indicates that the model can serve as a guideline for the quantitative control of C(²¹²Bi)/C(²¹²Pb).