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.

Methods for the experimental study of 220Rn homogeneity in calibration chambers.

This work presents two experimental methods for the evaluation of 220Rn homogeneity in calibration chambers. The first method is based on LSC of the 220Rn decay products captured in silica aerogel. The second method is based on application of solid state nuclear track detectors facing the air of the calibration chambers. The performances of the two methods are evaluated by dedicated experiments. The repeatability of the LSC-based method, estimated as relative standard deviation of the LSC measurements of ten silica aerogel samplers exposed under the same conditions is found to be 1.6%. Both methods are applied to study thoron homogeneity in the commercially available 50 L AlphaGuard emanation and calibration container, which was empty and its fan was turned on. It was found that the 220Rn distribution in this case is homogeneous within 10%. Both methods are also applied to test the thoron homogeneity in the BACCARA chamber at IRSN during a thoron calibration exercise. The results show that, at the centre of the chamber where the inputs of the sampling systems of the radon/thoron detectors were put close to each other, the thoron inhomogeneity is less than 10%. However, regions of higher thoron concentrations are clearly identified near the walls and the upper part of the chamber, with 220Rn concentrations being up to 60% higher compared to the concentration at the reference point. These results highlight the importance of the control and assessment of thoron homogeneity in thoron calibrations and in the cases when radon monitors are checked for thoron influence.

Study of two different coincidence counting algorithms in TDCR measurements.

This work presents a comparison of two different logics for imposing extending-type dead-time in TDCR measurements: the common dead-time (CDT) and the individual dead-time (IDT) counting logics. The CDT is implemented in the widely used MAC3 TDCR counting module and the IDT was recently implemented in the nanoTDCR counting device. The performance of the two counting algorithms is evaluated by three experimental setups and a dedicated Monte Carlo (MC) code for the simulation of realistic TDCR events. An excellent agreement is observed between the two counting logics for measurements of the pure ß-emitting radionuclides 3H, 14C, 63Ni and 90Sr/90Y for which the relative deviations in measured activities are in all cases less than 0.27%. For the measured 222Rn sources, we observe relative deviations up to 0.25% between the logical sum of double coincidences counting rates obtained with the two counting logics. The differences are in the double coincidence counting rate estimates which propagate to the estimates of the activity. Excellent agreement was observed between the CDT and IDT in MC simulated measurements of 3H where relative deviations are less than 0.24% for activities up to 70 kBq. The IDT counting algorithm seems to have an advantage in this particular case as it results in the same counting rates and calculated activities but with a significant reduction in the double coincidences dead-time.

Unperturbed, high spatial resolution measurement of Radon-222 in soil-gas depth profile.

This work presents a method for measuring the depth distribution of 222Rn activity in soil gas. The method is based on the capacity of polycarbonates to absorb 222Rn and on the possibility of performing sensitive measurements of 222Rn absorbed by the polycarbonates via liquid scintillation counting (LSC). The method is the following: cylindrical holes are drilled along a metal rod and Makrofol® N polycarbonate foils enclosed in polyethylene envelopes are placed in each hole. The rod is driven into the soil and kept for a certain time. As long as the rod is in the soil, the polycarbonate foils are exposed to the 222Rn concentration at their depth. At the end of the exposure the rod is pulled out and the foils are transferred to liquid scintillation (LS) vials filled with liquid scintillator. The 222Rn absorbed in the foils is then measured with a LS analyzer. The rod with the polycarbonate foils acts as a passive probe which senses the 222Rn concentration at different depths beneath the ground surface. The achievable minimum detectable 222Rn activity concentration with the equipment and conditions used in this study is around 12.5 kBq/m3. It can easily be lowered below 1 kBq/m3 if larger foils and low-background LS analyzers are used. Since the method does not require air sampling the depth distribution of 222Rn in the soil is unperturbed by the sampling. The spatial distribution and the maximum measurement depth are set by the distance between the holes and the depth to which the rod can be fixed into the ground. Results from in situ applications of the method in terrains with high 222Rn in soil-gas are reported, which demonstrate the feasibility and the usefulness of the proposed approach.

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.

RADON-222 IN SOIL-GAS MEASUREMENTS BY COMPACT DISCS. COMPARISON TO DIFFUSION CHAMBER MEASUREMENTS.

This work presents the results from simultaneous measurements of 222Rn in soil-gas by compact discs (CDs) and diffusion chambers. The measurements were performed in three terrains with high, medium and low 222Rn-in-soil-gas concentrations. Good correlations between the CD measurements and the reference diffusion chamber measurements are observed. The results indicate that it is important to apply temperature correction in the CD measurements, in order to account for the actual temperature during the exposure of the CDs in the soil.

Diffusion lengths and partition coefficients of 131mXe and 85Kr in Makrofol N and Makrofol DE polycarbonates.

This work presents the results of an experimental study of the Makrofol® N and Makrofol® DE polycarbonate foils absorption properties of 85Kr and 131mXe. The diffusion lengths of 85Kr and 131mXe in both types of foils are determined. The partition coefficients of 85Kr from air and water and that of 131mXe from air in Makrofol® N are determined. The partition coefficients of 85Kr from water and 131mXe from air in Makrofol® DE are also determined. The parameters are determined for T = 22°C and allow for the full characterization of sorption and desorption of 85Kr and 131mXe in the foils at this temperature. The results from this study highlight the remarkable absorption ability of Makrofol® and especially of the Makrofol® N foil and show that it surpasses the Makrofol DE® foil not only as a Rn absorber, but also as Kr and Xe absorber.

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

Radon (222Rn) and thoron (220Rn) levels in the environment are typically subject to significant random and systematic variations. Creation in the laboratory of reproducible and controlled exposure conditions close to that in the real environment can be useful for testing 222Rn and 220Rn detectors and for research. In this report the design and performance of a novel laboratory facility with such functionality is presented. The facility allows the exposure of detectors under controlled dynamic as well as static activity concentrations of 222Rn and 220Rn (pure and mixed) and temperature. The temperature is measured and regulated within -15 °C ÷ +60 °C by a dedicated programmable thermostat. Different reference activity concentrations in the exposure vessel are made by regulating the flow-rate of the air that flushes 222Rn/220Rn activity from the sources towards the exposure vessel. Reference atmospheres that contain 222Rn, 220Rn or a specified ratio of the two can be created. Pilot experiments that demonstrate the feasibility of the approach are presented. They include follow-up of a pre-defined temperature profile (in the range -5 °C ÷ +35 °C), test of the correspondence between planned and measured 222Rn and 220Rn activity concentrations, follow-up of a pre-defined dynamic profile of 220Rn concentrations and test of the possibility to create mixed 220Rn/222Rn atmospheres (experimentally checked for ratio of the activity concentrations from 0.27 to 4.5). The results from the experimental tests are in agreement with the values obtained by the developed theoretical model. The proposed approach can be used to plan and create stationary and dynamic reference exposure conditions that are close to the real exposure regimes in the environment.

Influence of the type of CD case on the track density distribution in CDs exposed to thoron.

A novel approach for retrospective thoron (Rn-220) measurements in buildings was recently proposed. It employs CDs/DVDs as detectors, in which the alpha-tracks formed by thoron's progeny Po-212 are analyzed. Compact disks and DVDs that had been stored in their cases are suitable, because the case provides a fixed and reproducible geometry of the Po-212 source. Since the measurement and calibration procedures involve analysis of different pieces of the disk, it is important to test the homogeneity of the track density over the disk area. This report presents results of such a study, in which disks in different containers were exposed to thoron. In almost all disks, the track density was inhomogeneous, increasing significantly near the holes in the container through which thoron could enter. However, as demonstrated, in disks regularly used and randomly rotated in their containers, the track density is expected to homogenize. It is concluded that the homogeneity of the tracks should be tested in disks exposed to thoron in homes and should be estimated or compensated in calibration exposures.

Determination of (222)Rn absorption properties of polycarbonate foils by liquid scintillation counting. Application to (222)Rn measurements.

This work demonstrates that a Liquid Scintillation Counting (LSC) technique using a Triple to Double Coincidence Ratio counter with extending dead-time is very appropriate for the accurate measurement of (222)Rn activity absorbed in thin polycarbonate foils. It is demonstrated that using a toluene-based LS cocktail, which dissolves polycarbonates, the (222)Rn activity absorbed in thin Makrofol N foil can be determined with a relative standard uncertainty of about 0.7%. A LSC-based application of the methodology for determination of the diffusion length of (222)Rn in thin polycarbonate foils is proposed and the diffusion length of (222)Rn in Makrofol N (38.9±1.3µm) and the partition coefficient of (222)Rn in Makrofol N from air (112±12, at 20°C) and from water (272±17, at 21°C) are determined. Calibration of commercial LS spectrometers for (222)Rn measurements by LSC of thin polycarbonate foils is performed and the minimum detectable activities by this technique are estimated.

Metrological tests of a 200 L calibration source for HPGE detector systems for assay of radioactive waste drums.

In this work we present test procedures, approval criteria and results from two metrological inspections of a certified large volume (152)Eu source (drum about 200L) intended for calibration of HPGe gamma assay systems used for activity measurement of radioactive waste drums. The aim of the inspections was to prove the stability of the calibration source during its working life. The large volume source was designed and produced in 2007. It consists of 448 identical sealed radioactive sources (modules) apportioned in 32 transparent plastic tubes which were placed in a wooden matrix which filled the drum. During the inspections the modules were subjected to tests for verification of their certified characteristics. The results show a perfect compliance with the NIST basic guidelines for the properties of a radioactive certified reference material (CRM) and demonstrate the stability of the large volume CRM-drum after 7 years of operation.

A high-sensitivity method for the measurement of 222Rn based on liquid scintillation counting of polycarbonate powder.

This work describes a technique for the measurement of 222Rn by absorption in polycarbonate (PC) powder and liquid scintillation counting (LSC). The work is an improvement of the recently proposed method for 222Rn measurements by LSC of exposed PC grains. It is demonstrated that the use of PC powder as a 222Rn sampler improves 13.6 times the sampling efficiency and leads to 6.5 times smaller minimmal detectable activity concentrations (MDAC) compared with the PC grains used so far. For a 40-h exposure of 7.4-g PC powder to 222Rn in air, the MDAC with a RackBeta 1219 LS counter is 62 Bq m(-3) (assuming a 8-h sample counting time and 24-h background time). For the same conditions the estimated 222Rn MDAC with a Quantulus 1220 LS counter is 20 Bq m(-3). The proposed technique is suitable for radon in air and radon in soil-gas measurements.

Liquid scintillation counting of polycarbonates: a sensitive technique for measurement of activity concentration of some radioactive noble gases.

This work explores the application of the liquid scintillation counting of polycarbonates for measurement of the activity concentration of radioactive noble gases. Results from experimental studies of the method are presented. Potential applications in the monitoring of radioactive noble gases are discussed.

Minimally invasive approach to thyroid gland surgery--indications, methods, first results.

UNLABELLED: After the introduction of minimally invasive operative techniques in the surgery of organs located in body cavities, extensive work has been done in the last five years with respect to their application in thyroid gland surgery as well. MATERIALS AND METHODS: In 2011, 406 patients underwent thyroid surgery at the Department of Surgery, Kaspela General Hospital for Active Treatment EOOD - Plovdiv. The study involved 48 of these patients, chosen at random and divided into two groups (A-minimally invasive thyroidectomy (MIT) - 26 patients, and B - minimally invasive video-assisted thyroidectomy (MIVAT) - 22 patients). All patients included in the study were selected on the basis of presence of one or more indeterminate nodules (fine needle aspiration biopsy - FNAB) sized up to 3.5 cm, with normal size of the thyroid gland up to 20-25 cm2, detected by preoperative ultrasonography. The study excluded patients with recurrent goitre, malignant disease of the thyroid gland and evidence of preoperative radiation therapy in the area of the head, neck and/or upper mediastinum. The preoperative investigation included history, physical examination, blood indices, echography, gamma camera and FNAB. Sensation of pain was evaluated by the patients according to a visual analogue scale, where lack of pain was evaluated as 0, and the most severe pain was evaluated as 10. RESULTS: The average duration of the hospitalization of patients undergoing MIT was 16 +/- 3.14 hours, whereas the patients undergoing MIVAT had to stay at the hospital for 18 +/- 3.56 hours. No complications were registered regarding the recurrent laryngeal nerves (RLN), as well as the operative wound. It should be noted that in all patients the course of the respective RLN was identified during the operative intervention, visually in most cases, or by electrostimulation. Postoperative hypoparathyroidism, registered by measuring the level of serum calcium, was observed in one visual analogue scale, as well as in the administration of pain-relieving agents during hospitalization. Other complications were not registered for the follow-up period, which covered an average of 6.56 +/- 3.14 months. CONCLUSIONS: The clinical analysis of the patients observed gave us grounds to draw the following conclusions: 1. The minimally invasive approach in patients with thyroid gland pathology is a possible and favourable option in selected patients with size of the gland within certain limits and not suffering from severe concomitant diseases. 2. The results in both groups of patients were comparable and did not show significant difference.

Determination of the diffusion coefficient and solubility of radon in plastics.

This paper describes a method for determination of the diffusion coefficient and the solubility of radon in plastics. The method is based on the absorption and desorption of radon in plastics. Firstly, plastic specimens are exposed for controlled time to referent (222)Rn concentrations. After exposure, the activity of the specimens is followed by HPGe gamma spectrometry. Using the mathematical algorithm described in this report and the decrease of activity as a function of time, the diffusion coefficient can be determined. In addition, if the referent (222)Rn concentration during the exposure is known, the solubility of radon can be determined. The algorithm has been experimentally applied for different plastics. The results show that this approach allows the specified quantities to be determined with a rather high accuracy-depending on the quality of the counting equipment, it can be better than 10 %.

Radon mapping by retrospective measurements - an approach based on CDs/DVDs.

This article points out the ability to map retrospective (222)Rn concentrations by home stored CDs/DVDs. The method employs the high radon absorption ability of the polycarbonate material of CDs and DVDs and their track-etch properties. The principle steps for the application of the method are addressed. The possibility for individual a posteriori calibration is studied, demonstrating that better than 10% accuracy in retrospective measurements is potentially achievable. Results from retrospective measurements in three different regions are shown, demonstrating the potential of the method for large-scale radon mapping. Comparison with independently evaluated retrospective (222)Rn concentrations in places with known radon history was made and very good correspondence was observed. The experience indicates that the method can be used for large scale retrospective radon mapping and its applications can be expanded towards mapping of radon concentrations in water and soil gas.

Analytical calculations of counting losses in internal gas proportional counting.

In internal gas proportional counting, the evaluation of counting losses is important in order to obtain high accuracy measurement results. In this paper, counting losses due to the wall effect and not counted beta particles with very low energy are evaluated by analytical calculations. The calculated and experimental results are compared and a very good agreement is found.