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1

Indoor and outdoor 222Rn and 220Rn and their progeny levels surrounding Bayan Obo mine, China

Wang Nanping, Hu Miao, Zeng Weihua, Yu Cong, Jia Binlin, Yang Zhijie

Nukleonika

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2020

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Vol. 65, No. 2

145--148

EN

More than half of the total natural ionizing radiation dose received by the human population is caused by radon and thoron (Rn and Tn) and their progeny. To estimate the level of radiation due to radon and thoron and their progeny, an investigation was conducted in a residential area near the world’s largest open-pit mine of Bayan Obo in Inner Mongolia, China. The concentration of Rn, Tn, and their decay products in air and soil were studied by using AlphaGUARD, RAD7, and ERS-RDM-2S for a discrete period of time in three different locations. The average indoor concentration of radon and thoron was 62.6 ± 44.6 Bq/m3 and 108.3 ± 94.5 Bq/m3 respectively, and the outdoor concentration was 12.9 ± 6.3 Bq/m3 and 55.8 ± 18.5 Bq/m3 , respectively. Relatively high concentrations were recorded in the area near to the mine, with a significant increasing trend observed in indoor thoron concentration. A prominent hotspot in thoron concentration was found in a single-story house with values 747 ± 150 Bq/m3 . The equilibrium equivalent thoron concentration (EECTn) varies from 0.48 Bq/m3 to 2.36 Bq/m3 with an arithmetic mean of 1.37 ± 0.64 Bq/m3 , and comparatively higher than EECRn. Concluding that the mining activity at Bayan Obo mine is significantly increasing the level of indoor thoron and its progeny in surroundings. It is suggested to further systematically investigate the indoor Rn and Tn progeny concentrations in the residential dwellings of the Bayan Obo mining area, and 232Th content of the building materials, to provide a basis for calculating the radiation dose.

2

Exposures from radon, thoron, and thoron progeny in high background radiation area in Takandeang, Mamuju, Indonesia

Saputra Miki Arian, Nugraha Eka Djatnika, Purwanti Tri, Arifianto Rokhmat, Laksmana Roza Indra, Hutabarat Richard P., Hosoda Masahiro, Tokonami Shinji

Nukleonika

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2020

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Vol. 65, No. 2

89--94

EN

The exposure from radon, thoron, and thoron progeny was measured for 45 dwellings in high background radiation area in Takandeang, Indonesia with ambient dose equivalent rate ranging from 0.34 µSv•h-1 to 1.90 µSv•h-1 . The measurement was taken using passive radon and thoron discriminative detector and thoron progeny detector. This measurement was taken from November 2018 to October 2019, and within one month the detector would be replaced with a new detector. The concentrations of radon, thoron, and thoron progeny were calculated as 42–490 Bqm−3 , 20–618 Bqm−3 , and 4–40 Bqm−3 , respectively. The concentrations for outdoor were 49–435 Bqm−3 , 23–457 Bqm−3 , and 4–37 Bqm−3 , respectively, and the annual effective dose was 9.8–28.6 mSv•y-1 . Based on the result of Spearman’s correlations analysis between the indoor radon and thoron concentrations and between the indoor thoron progeny and thoron concentrations, we suggest that exposure to thoron cannot be predicted from exposure to radon, and the equilibrium equivalent thoron concentration has a large uncertainty when it is estimated from thoron concentration assuming a single thoron equilibrium factor.

3

The presence and dosimetry of radon and thoron in a historical, underground metalliferous mine

Kleinschmidt R., Watson D., Janik M., Gillmore G.

Journal of Sustainable Mining

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2018

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Vol. 17, iss. 3

120--130

EN

A combination of long term passive, and short term active radon-222, radon-220 and respective progeny measurements were conducted in both traverse and longitudinal axes of a historical metalliferous underground mine in North Queensland, Australia. While the passive monitor results provided average radon and thoron air concentrations over periods of 70-90 days, active measurements over a four day period provided significantly more detail into the dynamics of radon and progeny concentrations in the naturally ventilated mine environment. Passive monitor concentrations for radon and thoron ranged between 60 and 390 Bq m-3 (mean: 140 ±55 Bq m-3) and 140 and 2600 Bq m-3 (mean: 1070 ±510 Bq m-3) respectively, with passive thoron progeny monitors providing a mean concentration of 9 ±5 Bq m-3EEC. Active measurement mean concentrations for radon, thoron, radon progeny and thoron progeny in the centre of the mine drive were 130 ±90 Bq m-3, 300 ±100 Bq m-3, 20 ±20 Bq m-3EEC and 10 ±10 Bq m-3EEC respectively. It was identified that thoron passive detector placement is critical in establishing reliable monitoring data, and is the reason for the discrepancy between the active and passive thoron results in this study. Site specific progeny measurements are required for the accurate estimation of dose to persons entering the mine. Based on short term active measurements and passive thoron progeny monitor results, the dose contribution from thoron and progeny in the mine was observed to contribute up to 80% of the total radon/thoron inhalation dose, and therefore should not be underestimated in monitoring programs under similar conditions.

4

Thoron emanation and exhalation of Slovenian soils determined by a PIC detector-equipped radon monitor

Jónás J., Sas Z., Vaupotic J., Kocsis E., Somlai J., Kovács T.

Nukleonika

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2016

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Vol. 61, No. 3

379--384

EN

The health risk from thoron (Rn-220) is usually ignored owing to its short half-life (55.6 s), but the generated thoron decay products can cause a significant dose contribution. In this study, altogether 51 Slovenian soil samples were investigated using an accumulation chamber technique to obtain information about thoron exhalation features. The obtained (massic) thoron exhalation results varied between 6.9 and 149 mBq•kg–1•s–1 (average: 55.2 mBq•kg –1•s–1). The Th-232 content was determined using HPGe gamma spectrometry. The Th-232 activity concentration ranged between 9.3 and 161.7 Bq•kg–1 (average: 64.6 Bq•kg –1). The thoron emanation features were also calculated from the obtained results (2.9 to 21.2% with an average of 8.6%). The thoron exhalation and emanation properties were compared with the radon exhalation and emanation features determined in a previous study. It was found that there was no correlation between the radon and thoron emanation features, according to the obtained data. This can be explained by the different Ra-224 and Ra-226 distributions in the soil grains. As a result, the thoron emanation factor cannot be predicted from radon emanation and vice versa.

5

The effect of CO2 on the measurement of 222Rn and 222Rn with instruments utilising electrostatic precipitation

Lane-Smith D., Sims K.

Acta Geophysica

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2013

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Vol. 61, no. 4

822--830

EN

In some volcanic systems, thoron and radon activity and CO2 flux, in soil and fumaroles, show a relationship between (220Rn/222Rn) and CO2 efflux. It is theorized that deep, magmatic sources of gas are characterized by high 222Rn activity and high CO2 efflux, whereas shallow sources are indicated by high 220Rn activity and relatively low CO2 efflux. In this paper we evaluate whether the observed inverse relationship is a true geochemical signal, or potentially an analytical artifact of high CO2 concentrations. We report results from a laboratory experiment using the RAD7 radon detector, known 222Rn (radon) and 220Rn (thoron), and a controllable percentage of CO2 in the carrier gas. Our results show that for every percentage of CO2, the 220Rn reading should be multiplied by 1.019, the 222Rn radon should be multiplied by 1.003 and the 220Rn/222Rn ratio should be multiplied by 1.016 to correct for the presence of the CO2.

6

Radon-thoron monitoring in tatun volcanic areas of northern Taiwan using LR-115 Alpha track detector technique: Pre-calibration and installation

Kumar A., Walia V., Yang T., Chang H., Lin S., Eappen K., Arora B

Acta Geophysica

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2013

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Vol. 61, no. 4

958-976

EN

In the present study, experiments have been carried out to calibrate LR-115 alpha detector films in bare and cup-mode exposure for the measurement of radon and thoron concentrations in soil gas. Results showed non-uniformity in track formation on the films in bare-mode exposure. However, in cup-mode exposure the non-uniformity was reduced to a greater extent. The calibration factors obtained for radon in bare- and cup-mode exposures are 0.049 and 0.034 tr. cm−2 per Bq m−3 d, respectively. An attempt has been made to calibrate the radon-thoron discriminative cup with LR-115 films for simultaneous measurements of radon and thoron. This paper also presents the preliminary results of radonthoron monitoring in Tatun volcanic areas of northern Taiwan for the first time using radon-thoron discriminators with LR-115 films. The results show that the safe temperature to install the LR-115 films in volcanic areas is ≤ 65°C and thoron concentration in the study area is low.

7

Thorium nuclear fuel - thoron aspect

Zagórski Z. P., Głuszewski W.

Nukleonika

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2010

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Vol. 55, No. 3

407-408

EN

The communication reports a serious complication connected with preparation, storage and transportation of fuel for thorium and uranium/thorium nuclear reactors. Whereas uranium fuel of any degree of enrichment is free from radium, which produces radon-222, thorium itself produces thoron (radon-220). Measurement of thoron by a routine ionization-chamber device around a small sample of 2 g thorium dioxide shows already the health endangerment situation. The presence of thoron is also confirmed by a typical solid state dosemeter (polymer CR-39), exposed to the air around ThO2 and etched afterwards with warm NaOH solution. The unavoidable presence of thoron can cause increase of price of production of nuclear fuel, demanding special approach to the method of manufacture.

8

Specific properties of a model of thoron and its decay products in indoor atmospheres

Meisenberg O., Tschiersch J.

Nukleonika

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2010

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Vol. 55, No. 4

463-469

EN

Whereas several models of indoor concentrations of radon and its decay products exist, mod els for the occurrence and spatial distribution of thoron (220Rn) and its decay products are lacking. This study highlights the specific properties of the thoron decay chain and presents their consequences for a thoron model. The short half-life of thoron results in an inhomogene ous spatial distribution, which is determined by diffusive and advective transport. The long half- -life of the decay product 212Pb accounts for a strong influence of air exchange on its overall concentration as well as on its unattached fraction. It could further be predicted that also the unattached part of 212Pb is distributed inhomogeneously. The theoretical structure of a thoron model, which can neglect the most short-lived decay products but must account for the influence of air exchange in a stronger way than it is the case for radon, results from these considerations.

9

Radon and thoron parallel measurements in dwellings nearby a closed Hungarian uranium mine

Németh C., Jobbágy V., Kávási N., Somlai J., Kovács T., Tokonami S.

Nukleonika

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2010

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Vol. 55, No. 4

459-462

EN

Integrated measurements of radon (222Rn) and thoron (220Rn) were executed in a Hungarian village, located in the vicinity of an abandoned uranium mine. The applied passive radon and thoron monitor was the RADUET which is based on a CR-39 track detector. The investigated 35 houses were one storey buildings made of bricks. The rock under the village is a gray-sandstone with an average of 136 and 77 Bqźkg–1 uranium and thorium, respectively. The detectors were mostly placed in the inhabited areas of the houses, such as bedrooms and living-rooms, at a height of 1–1.5 m close to the wall. The measurement periods were between December 2006 and May 2007 and between May 2007 and February 2008. Annual averages of radon concentrations were calculated applying seasonal correction factors to the results of the two measurement periods. The results show that the radon concentrations in the case of considerable part of the investigated dwellings seems to be significantly higher than the Hungarian averages for ground-floor houses (152 Bqźm–3). The thoron concentrations in some cases are also not negligible indicating that radon measurements which are sensitive to thoron can be misleading. Additionally, thoron can also be a contributor of extra dose.

10

Possible role of radon in prebiotic chemistry and in early evolution of Life on Earth

Zagórski Z. P.

Nukleonika

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2010

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Vol. 55, No. 4

555-558

EN

Radon in the environment of early Earth was present in sites, determined by location of deposits of uranium, in very different geological formations. According to the decay of uranium-238, the total production of radon at the beginnings was twice as high as now and was continuously diminishing to the present levels. This nuclide could not play as big a role as do radioactive elements connected with the presence of high concentration of 235U, which was high enough in some places to give rise to formation of natural nuclear fission reactors (e.g. Oklo phenomenon in Africa). The main role of ionizing radiation in prebiotic chemistry and biological evolution was played by low LET (linear energy transfer) radiations, as deep penetrating sources of external energy. High LET radiations are of low penetration and could act only superficially. Radon is an exception, due to its easy transfer in the air. Therefore, it could play a role already in the cases of these early organisms which exhibited the gaseous exchange of chemical compounds with the surrounding atmosphere. The action was destructive, but, on the other hand, was also mutagenic. Nevertheless, the general quantitative effect of radon on the global scale could not be larger than of other radioactive nuclides. Presented considerations are part of the chapter by the present author on the role of nuclear and radiation chemistry in astrobiology, in the monograph published by American Scientific Publishers [1].

11

Dynamics of radon and its decay products inside an accumulative chamber

Yakovleva V. S.

Nukleonika

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2010

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Vol. 55, No. 4

595-600

EN

The calculations of radon and its decay products accumulation dynamics inside a chamber designed for measurements of radon flux density from the soil surface were carried out in the present work. Dynamics of alpha-,beta-particles and gamma-ray yields under decay of accumulated radionuclide nuclei was calculated based on the accumulated activity. Ion production rate inside the accumulative chamber due to ionizing radiation of different types was estimated. Thoron and its decay products accumulation regularities inside the accumulative chamber were also estimated and potential effect of thoron on measurement results (if counting regime is used) was analyzed in detail. Dynamic equations of the studied radiation characteristics, their solutions and obtained results analysis are presented.

12

Test measurements of thoron concentration using two ionization chambers AlphaGUARD vs. radon monitor RAD7

Kochowska E., Kozak K., Kozłowska B., Mazur J., Dorda J.

Nukleonika

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2009

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Vol. 54, No. 3

189-192

EN

The experiment aiming at testing the possibility of using AlphaGUARD monitors based on an ionization chamber for thoron measurements is presented. A single AlphaGUARD monitor working in the flow mode was applied to measure thoron concentration in the radon-free atmosphere. The sensitivity (correction factors) of the monitor to thoron was estimated by comparison with a RAD7 portable detector (Durridge Company), based on spectrometric analysis, in the thoron, radon-free atmosphere in a calibration chamber. This depends on the applied flow rate and changes from 8% for the flow rate of 0.3 dm3/min to 36% for 1 dm3/min. It was also revealed that the sensitivity of the monitor to thoron in the diffusion mode is equal to ca. 5% and may be neglected. The method involving two Alpha-GUARD monitors working in two different modes (diffusion and flow) at the same time may be used to evaluate radon and thoron concentration in the natural environmental conditions where usually both isotopes appear together. In this method thoron concentration is estimated as the difference of results obtained from two AlphaGUARD monitors multiplied by the correction factor corresponding to the applied flow rate. The devices based on spectrometric analysis, e.g. RAD7 seem to be a better tool for thoron measurements in the environmental conditions.

13

Measurement of radon (222Rn) and thoron (220Rn) concentration with a single scintillation cell

Machaj B., Urbański P., Bartak J.

Nukleonika

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2007

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Vol. 52, nr 4

167-171

EN

. A single scintillation cell (ö 54 × 74 mm) is used for the measurement of radon and thoron. The radon and thoron laden air is filtered and forced to flow at 1 dm3/min through the scintillation cell in the period of 1 10 min. The count number from alpha radiation is registered in the periods of 3 10 min and 20 30 min. Two values of detection and deposition efficiency of alpha radiation are used for radon (at air flow and air at rest in the cell) and for thoron. Measurements of radon laden air and thoron laden air showed good agreement between the reference concentration and the measured concentration, not worse than 1% for radon and not worse than 2% for thoron. Combination of radon + thoron concentration showed also a small interference ("cross talk") not worse than 1%.