Thoron Activity Research Articles

Soil radon and thoron studies near the mofettes at Harghita Bai (Romania) and their relation to the field location of fault zones

AbstractIn the aftermath of postvolcanic activity, dry gases, containing mainly CO2, bring along radioactive gases such as radon (222Rn) and thoron (220Rn) that migrate together to the surface. Tectonic faults facilitate the upward migration of these gases. The study described here is based on measurements of radon and thoron activity concentrations performed around the mofettes and mineral springs at Harghita Bai, Harghita Mts. (part of the Neogene Volcanic region of the Eastern Carpathians, Romania). The aim of the study was to identify the location and the direction of the fault system that controls the occurrence of the two mofettes, as well as the mineral springs in the resort by means of systematic measurements of soil radon and thoron activity concentrations. During fieldwork, the existence of the presumed fault system across two different profiles, normal to assumed fault directions, was examined. We sought to identify the local fault hypothetically traced across the two mofettes directed at N 50°W. We also considered the major fault system connecting mofettes and mineral springs, whose direction is N 5°E. For radon and thoron concentration determinations in soil gas, we used a main measurement method (a LUK3C scintillation detector with Lucas cells). Results showed normal distributions for the activity concentrations for both radon and thoron, with a maximum value in both cases. The concentrations for radon and thoron were in the range of several kBq m−3 to tens of kBq m−3. The distributions are consistent with the hypothesis that the fault lines cross at the point corresponding to maximum values of the radon and thoron concentrations. From the results it is also clear that high precision thoron concentration determinations provided a more accurate location for this type of geological environment than for radon alone, because of its shorter half‐life and its shorter migration length.

Use of exhaled thoron activity measurement system in radiological labor hygiene

在稀土开发、冶炼过程中,工人有可能吸入一定量的含钍粉尘,其矿尘中含有一定量的放射性钍.钍在工业上用途也十分广泛,作业工人也有吸入钍尘和钍射气短寿命子体的可能.作业人员在生产场所长期吸入钍和钍射气短寿命子体对其健康可能产生负面影响,并有可能诱发肺癌.对这些生物学效应进行量化确认的关键是其体内实际的钍的活度以及测量方法的准确性。

The establishment of a portable high sensitivity exhaled thoron activity measurementsystem

A portable system, using electrostatic collection, for the measurement of exhaled thoronactivity in humans is described, together with details of the basic theory, equipment,calibration procedures, measurement and preliminary use. The portable system built onexperience at the Argonne National Laboratory (ANL) to achieve a reduction inmeasurement time from 30 h to 200 min, and to increase the total efficiency ofthe system from 50% (at ANL) to 70%. The limit of detection of the system(2σ above zero) is 0.007 Bq of thoron activity outside the body. The totalstandard error of this system is 47% for a thorium lung burden of0.22 Bq. The average background of this scintillation detector was 0.003counts min−1.

Radon concentration levels in dry CO2 emanations from Harghita Băi, Romania, used for curative purposes

The aim of this work is to study the exposure due to the radon of the patients from the dry carbon dioxide baths (mofettas) from Harghita Băi, Romania. These mofettas consist of emanated gas with high carbon dioxide content, and proved curative effects. The vertical and horizontal distribution of the radon activity concentration was monitored indoor, the seasonal variation, as well as the soil radon and thoron activity concentration outdoor, in the vicinity of the bath to determine the origin of the radon and the location of the fault through which it propagates. The equilibrium factor of the baths and the effective dose received by the patients was also calculated.

The radiological impact of the presence of radon, thoron and their progeny in the environment of a liquid petroleum gas bottling plant

The seasonal variation of the activity of radon, thoron and their progeny has been measured, and the annual exposure, lifetime fatality risk and annual effective dose to the workers in a Liquid Petroleum Gas (LPG) bottling plant due to exposure from a mixed field of radon and thoron have been calculated over the four seasons of the year. The measurements were carried out using a passive time-integrated track etch technique employing LR-115 (type II) Solid State Nuclear Track Detectors (SSNTDs) in plastic twin-chamber dosimeter cups. The average value of the radon activity varied from 17.78 Bq/m³ to 49.01 Bq/m³ in different seasons. The minimum value of the radon activity was found to be 7.78 Bq/m³ in summer (April to July), whereas the maximum value was found to be 59.01 Bq/m³ in winter (October to January). The average value of the thoron activity varied from 8.16 Bq/m³ to 33.74 Bq/m³ in different seasons. The minimum value of the thoron activity was found to be 1.16 Bq/m³ in summer (April to July), whereas the maximum value was found to be 65.08 Bq/m³ in winter (October to January). The average value of the Potential Alpha Energy Concentration (PAEC) due to radon varied from 1.92 mWL to 5.30 mWL in different seasons. The minimum value of the PAEC due to radon was found to be 0.84 mWL in summer (April to July), whereas the maximum value was found to be 6.38 mWL in winter (October to January). The average value of the PAEC due to thoron varied from 0.22 mWL to 0.91 mWL in different seasons. The minimum value of the PAEC due to thoron was found to be 0.03 mWL in summer (April to July), whereas the maximum value was found to be 1.76 mWL in winter (October to January). The annual exposure due to radon and thoron daughters, collectively, varied from 0.105 WLM to 0.218 WLM with an average value of 0.168 WLM. The lifetime fatality risk varied from 0.31 × 10−4 to 0.65 × 10−4 with an average value of 0.50 × 10−4. The annual effective dose from radon and thoron (PAEC) varied from 0.40 mSv to 0.84 mSv with an average value of 0.64 mSv. The findings suggest that the bottling plants may affect doses from external irradiation, and the inhalation of radon decay products is significant from the health point of view.

Simultaneous measurement of radon and thoron using Lucas scintillation cell

A method has been developed for the simultaneous measurement of radon ( Rn 222 ) and thoron ( Rn 220 ) in a mixed environment using the Lucas scintillation cell (LSC). The method uses counts from two arbitrary counting intervals from zero time with respect to sampling hence, called two count method (TCM). The basis of the method involves formulation of simultaneous linear equations with two unknown variables. The unknown variables represent the radon and thoron activities in the cell. The coefficients of the equations are the integrated activities of radon, thoron and their alpha decay products per unit activities of the parent radionuclides. The method can be used to estimate the radon and thoron concentrations in a mixed environment accurately and quickly, as there is no need to delay the counting to achieve complete decay of thoron. The mathematical basis of the method along with few experimental results is presented in this paper. Results yielded, on comparison, good agreement with the delay count method (DCM) and double filter measurement (DFM) technique. Multiple regression analysis is also carried out to get the concentrations of radon and thoron from the counts obtained for various counting intervals. The corresponding growth factors of radon and thoron also showed good comparison with the average concentrations obtained from the two count approach for different counting intervals. Use of LSC for routine environmental measurements has its limitation due to high minimum detection level (MDL) values. However, LSC is commonly used in uranium mines, high background radiation areas and in calibration experiments. The present methodology is a very convenient approach to measure radon and thoron simultaneously especially in calibration experiments.

Short- and long-term monitoring of radon, thoron and carbon dioxide in soil-gas at Altos de pipe, Venezuela

We have measured radon and thoron activities in soil-gases since July 9, 1997 Cariaco earthquake (Mw=6.9) until the end of 2000. Carbon dioxide concentrations were also monitored between 1998–2000. The soil-gas was collected between 50–55 cm depths at two sampling points at Altos de pipe (Instituto Venezolano de Investigaciones Cientificas-IVIC) near Caracas, Venezuela. The radon and thoron measurements were performed daily employing radiation monitors with scintillation cells and the carbon dioxide was monitored with portable gas analyzers. Average weekly and monthly values were calculated and plotted for this three-four year period. In general, both the radon and carbon dioxide values showed sinusoidal trends due to seasonal changes. During the dry season the radon and carbon dioxide values decreased, while the radon activity was relative constant (flat) during the rainy season at one of the sampling points. Only two monthly radon values were seen to be anomalous in the graphs in respect to seven anomalous periods for the average weekly values. No anomalous periods were clearly seen for carbon dioxide. Finally, it was difficult to try to relate these radon anomalous periods with specific earthquakes due to the large number of minor earthquakes during these years, but it seem that the minor earthquake (Mb=5.9) of October 4, 2000 could be associated with the radon anomalous period in September, when there were no other minor earthquakes (Mb≥4.0).

Development of a calibration facility for measurements of the thoron activity concentration

A new calibration facility for measuring the thoron ( 220 Rn) activity concentration in air is currently being developed at the Physikalisch-Technische Bundesanstalt (PTB). The system consists of a reference chamber of well-defined volume and several electrodeposited 228 Th sources. In order to produce and maintain a homogeneous and constant activity concentration, a flow field is created inside the reference chamber and monitored. The 220 Rn activity concentration is measured with a multi-wire ionisation chamber (MWIC) operating in pulse mode and externally connected to the reference chamber. With this method thoron fields with activity concentrations ranging from 1 to 10 kBq/ m 3 are presently produced with an overall relative standard uncertainty of less than 5%.

Use of an alpha-spectrometer method to measure the equivalent equilibrium volume activity of radon in dwellings and industrial premises

An instrument (the RAMON-01) which enables the equivalent equilibrium volume activity of radon and thoron to be measured rapidly and with high accuracy is developed.

Study of the influence of the lithological and hydrogeological parameters of aquifers on the radon emanation from underground waters using solid state nuclear track detectors

Radon-to-thoron ratios as well as radon and thoron activity concentrations in different underground water samples belonging to different aquifers in the Moroccan Middle Atlas area have been evaluated by LR-115 and CR-39 solid state nuclear track detectors (SSNTD) using a new calibration method. The radon isotope (222Rn) was used as a tracer for studying the water exchange between different aquifers of the area studied. The influence of the lithological and hydrogeological parameters of the aquifers on radon emanation were investigated.

An observation on the clearance of thorium dioxide from the lung of a miner

We report the results of exhaled thoron activity measurements and thorium lung burden estimates performed on a subject during the period 1983 to 1990. They point clearly to a very very slow turnover of part of the intake by the lung. In view of the rarity of such data for human subjects, except for those injected with Thorotrast, the investigations and results are presented in some detail.

A follow-up study on the relationship between thorium lung burden and health effects on miners (1982-91)

The results of an investigation (1982-91) on the natural thorium lung burden and its health effects on miners in the Baiyan Obo mine are reported. An electrostatic collection system was used to measure the exhaled thoron activity. Measurements of exhaled thoron activity were carried out on 588 miners (985 measurements) who had inhaled thorium-containing dusts. Exhaled thoron activity was also determined on 124 persons (124 measurements), who had not inhaled thorium-containing dusts. The average thorium lung burdens of the 588 miners and the 124 controls were 0.85 Bq and 0.15 Bq, respectively. Of the 588 miners, 7 had a thorium lung burden higher than 3.7 Bq, 5 had a thorium lung burden higher than 4.44 Bq and 1 miner had the highest thorium lung burden of 5.56 Bq. In about 20% of these miners the thorium lung burden was 0.74 Bq. There was no definite increase in the incidence of lung cancers in more than 2000 miners who had inhaled thorium dusts and thoron daughters in the period 1958-90. Of the miners who had inhaled thorium dusts, there was a significant increase in the incidence of respiratory symptoms, lung function disorders and pneumoconiosis stage 0+ and stage 1. Based on the results of animal experiments and the low percentage of thorium in the dust, the authors suggest that disorders of the respiratory tract were due mainly to other chemical components in the dust, such as SiO2 and other chemical elements. The role of thorium is negligible. The average air thorium dust concentrations in the main workshops and the average thorium lung burden of the thorium dust-inhaling miners were lower by a factor of 20 and 3 respectively in 1991 compared with 1983.

Field Measurements of Radon Exhalation and Ra-226 Content in Soil using the Can-Technique

CR-39 and LR-115 plastic nuclear track detectors in the can-technique have been employed in the field measurements of radon exhalation, Ra-226 and U-238 content in dry-soil air at numerous regions in Sudan (the Blue and White Nile and Mogran regions). Measurements gave an average radon exhalation from the soil to the atmosphere and Ra-226 content of (23.4 ± 2.60) kBq · m−2 and (123 ± 13.65) Bq · kg−1 respectively. A polyethylene permeable membrane cover was used to eliminate the contribution of thoron activity inside the can. Assuming a radioactive equilibrium between the U-series, the average U-238 content in the soil was found to be (9.92 ± 1.01) ppm. This survey may be used for uranium prospection in soil.

Equations for mixed activities of atmospheric radon daughters collected on a filter

The activity of a filter through which air containing radon daughters has been sampled includes a mixture of alpha, beta and gamma radiations of the radon daughters collected on the filter. In this paper equations are given which can be used to determine concentrations of radon daughters in air by measuring counts due to this mixture of activities. The effect of the presence of thoron activity is also discussed.

Determination of the Thorium Content of Rocks

A new method for the determination of thorium in quantities of the order of 10—5 to 10—6 g is employed to complete the data necessary for the calculation of the age of geological material. The alpha-particle activity of thoron in a streaming gas is measured with a counter, a procedure which is shown to be superior to the usual ionization measurements on the thoron deposit. Simultaneously, the Pa/Ra ratio in common rocks can be determined.