Chutima Kranrod

International intercomparisons of integrating radon detectors in the NIRS radon chamber.

An international intercomparison of integrating detectors was conducted at NIRS (National Institute of Radiological Science, Japan) with a 24.4 m(3) inner volume walk-in radon chamber that has systems to control radon concentration, temperature and humidity. During the first intercomparison (05.2007) four groups participated from four countries and for the second intercomparison (10.2007) 17 participants were involved from 11 countries. Most of detectors are in good agreement with each other when compared to the radon level provided by the radon chamber. It appeared that the 70% of detectors are unified within the 20% margin of uncertainty.

Comparative analysis of radon, thoron and thoron progeny concentration measurements

This study examined correlations between radon, thoron and thoron progeny concentrations based on surveys conducted in several different countries. For this purpose, passive detectors developed or modified by the National Institute of Radiological Sciences (NIRS) were used. Radon and thoron concentrations were measured using passive discriminative radon-thoron detectors. Thoron progeny measurements were conducted using the NIRS-modified detector, originally developed by Zhuo and Iida. Weak correlations were found between radon and thoron as well as between thoron and thoron progeny. The statistical evaluation showed that attention should be paid to the thoron equilibrium factor for calculation of thoron progeny concentrations based on thoron measurements. In addition, this evaluation indicated that radon, thoron and thoron progeny were independent parameters, so it would be difficult to estimate the concentration of one from those of the others.

INTERNATIONAL INTERCOMPARISONS OF INTEGRATING RADON/THORON DETECTORS WITH THE NIRS RADON/ THORON CHAMBERS

Intercomparisons of radon/thoron detectors play an important role not only for domestic radon/thoron survey but also for international or interregional discussion about radon/thoron mapping in dwellings as well as that in the soil. For these purposes, it is necessary to improve and standardise technical methods of measurement and to verify quality assurance by intercomparisons between laboratories. Therefore, the first thoron international intercomparison was provided at the NIRS (National Institute of Radiological Sciences, Japan) thoron chamber with a 150 dm(3) inner volume. In addition, a second intercomparison of radon detectors was conducted at NIRS with a 24.4 m(3) inner volume walk-in radon chamber. Only etched-track detectors were used during thoron intercomparison as well as three types for the radon intercomparison: etched-track, charcoal and electret. In general, 45 % results for thoron experiment do not differ more than 20 % from the reference value of thoron concentration and 69 % for radon.

Mitigation of the effective dose of radon decay products through the use of an air cleaner in a dwelling in Okinawa, Japan

Field measurements were conducted to assess the effects of an air cleaner on radon mitigation in a dwelling with a high radon concentration in Okinawa, Japan. The measurements included indoor radon concentration, individual radon progeny concentration, equilibrium equivalent concentration of radon (EECRn), unattached fraction, and size distribution of aerosol-attached radon progeny. These measurements were conducted in a 74 m(3) room with/without the use of an air cleaner. The results showed that the mean radon concentration during the measurement was quite high (301 Bq m(-3)). The operation of air cleaner decreased the radon progeny activity concentration, EECRn and equilibrium factor by 33%, 57% and 71%, respectively, whereas the unattached fraction increased by 174%. In addition, the activity concentration of attached radon progeny in the accumulation mode (50-2000 nm) was obviously deceased by 42%, when the air cleaner was operated. According to dosimetric calculations, the operation of air cleaner reduced the effective dose due to radon progeny by about 50%.

Assessing diffusive fluxes and pore water radon activities via a single automated experiment

We present a laboratory system to evaluate radon flux and pore water radon via automated sediment equilibration experiments. The setup includes a measured mass of sediment and water inside a gas-tight reaction flask connected in a closed loop to a radon-in-air analyzer. Diffusive fluxes are determined either from the near-linear slope of the activity versus time over the first several hours or by running the experiment longer to estimate the equilibrium concentration via a curve fitting approach. By combining the equilibrium activity with relevant physical parameters, one can also estimate the pore water concentrations.

Comparative dosimetry of radon and thoron

There is a well-known discrepancy between dosimetrically derived dose conversion factor (DCF) and epidemiologically derived DCF for radon. As the latter DCFs, International Commission on Radiological Protection (ICRP) recommends a value of ∼6.4 nSv (Bq h m(-3))(-1) and 7.9 nSv (Bq h m(-3))(-1) for radon decay products (RnDP) in dwellings and workplaces, respectively. On the other hand, the dosimetric calculations based on the ICRP-66 respiratory tract model derived a DCF of 13 nSv (Bq h m(-3))(-1) and 17 nSv (Bq h m(-3))(-1) for RnDP in dwellings and workplaces, respectively, and 83 nSv (Bq h m(-3))(-1) for thoron decay products (TnDP) in dwellings. In addition, the DCFs derived from both approaches and UNSCEAR were applied to comparative dosimetry for two thoron-enhanced areas (cave dwellings in China and dwellings at a spa town in Japan), where the equilibrium equivalent concentration of radon and equilibrium equivalent concentration of thoron have been measured. In the case of the spa town dwellings, the dose from TnDP was larger than the dose from RnDP.

Preliminary Experiments Using a Passive Detector for Measuring Indoor 220Rn Progeny Concentrations with an Aerosol Chamber.

AbstractThis paper describes preliminary experiments using a passive detector for integrating measurements of indoor thoron (220Rn) progeny concentrations with an aerosol chamber. A solid state nuclear detector (CR‐39) covered with a thin aluminum-vaporized polyethylene plate (Mylar film) was used to detect only alpha particles emitted from 212Po due to 220Rn progeny deposited on the detector surfaces. The initial experiment showed that Mylar film with area density of more than 5 mg cm−2 was suitable to cut off completely alpha particles of 7.7 MeV from 214Po of 222Rn progeny decay. In the experiment using the passive detector, it was observed that the net track density increased linearly with an increase of time-integrating 220Rn progeny concentration. As a result of dividing deposition rates by atom concentrations, the deposition velocity was given as 0.023 cm s−1 for total 220Rn progeny. The model estimates of deposition velocities were 0.330 cm s−1 for unattached 220Rn progeny and 0.0011 cm s−1 for aerosol-attached 220Rn progeny using Lai-Nazaroff formulae. These deposition velocities were in the same range with the results reported in the literature. It was also found that the exposure experiments showed little influence of vertical profiles and surface orientations of the passive detector in the chamber on the detection responses, which was in good agreement with that in the model estimates. Furthermore, it was inferred that the main uncertainty of the passive detector was inhomogeneous deposition of 220Rn progeny onto its detection surfaces.

A comparative study of thorium activity in NORM and high background radiation area

Several industrial processes are known to enrich naturally occurring radioactive materials (NORM). To assess such processes with respect to their radiological relevance, characteristic parameters describing this enrichment will lead to interesting information useful to UNSCEAR. In case of mineral treatment plants, the high temperatures used in smelting and refining processes lead to high concentrations of (238)U and (232)Th. Also due to thermal power combustion, concentration of U and Th in the fly ash increases manifold. NORM samples were collected from a Thailand mineral treatment plant and Philippine coal-fired thermal power plants for investigation. Some studies are initiated from a high background radiation area near Gopalpur of Orissa state in India. These NORM samples were analysed by gamma-ray spectrometry as well as inductively coupled plasma mass spectrometry. The radioactivity in case of Orissa soil samples is found to be mainly contributed from thorium. This study attempts to evaluate levels of thorium activity in NORM samples.

Natural radionuclide concentrations in processed materials from thai mineral industries

The naturally occurring radioactive materials (NORMs) distributed in products, by-products and waste produced from Thai mineral industries were investigated. Samples were analysed for radioactivity concentrations of two principal NORM isotopes: (226)Ra and (228)Ra. The enrichment of NORM was found to occur during the treatment process of some minerals. The highest activity of (226)Ra (7 × 10(7) Bq kg(-1)) was in the scale from tantalum processing. The radium concentration in the discarded by-product material from metal ore dressing was also enriched by 3-10 times. Phosphogypsum, a waste produced from the production of phosphate fertilisers, contained 700 times the level of (226)Ra concentration found in phosphate ore. Hence, these residues were also sources of exposure to workers and the public, which needed to be controlled.

Determination of radon in natural gas pipelines

The aim of this study was to develop the methodology for collection and analysis of radon from a natural gas pipeline. Activated charcoal was used as collection media. Two methods were designed for collecting radon gas samples from onshore and offshore production sites. For onshore sites a continuous gas sampling method from the pipeline was developed. In case of offshore sites, a batch sampling method was designed. Gamma spectroscopy was utilized to determine the concentration of radon by analysis of radon daughters on the charcoal.