Scintillation Cell Research Articles

Development and application of a continuous measurement system for radon exhalation rate

A continuous measurement system, with a ventilation-type accumulation chamber, was developed for radon exhalation rate determination. A reasonable sampling flow rate for the measurement system was determined by comparing the values obtained by the system with those obtained by a grab sampling method. The sampling flow rate of passage through the scintillation cell from the accumulation chamber was varied from 0.05 to 2.0 l min(-1). The difference in pressure between the inside and outside of the accumulation chamber increased as the sampling flow rate became large, and the estimated radon exhalation rate also increased with the sampling flow rate. From these results, a reasonable sampling flow rate was estimated to be less than 0.2 l min(-1).

A simple radon chamber for use with soil gas for calibration of radon measuring devices and instruments

A simple and easy to use radon calibration chamber of volume of 216 litres was designed and constructed for applications in calibration of radon measuring devices and for research studies. The main advantage of this chamber is that instead of using 226 Ra source to generate the 222 Rn inside the chamber, soil gas is utilised as a source of 222 Rn. Soil gas is drawn from the soil using a pump to fill the chamber in order to obtain radon with high concentrations inside the chamber. The advantage of this technique is that the desired radon concentration (ranging from few Bq/m 3 to about kBq/m 3 ) can be attained easily and fast at any time by filling the chamber with different volumes of soil gas. After demonstrating the usefulness of the technique, calibration experiments were carried out for radon measuring devices (charcoal canisters and scintillation cell) using the calibration chamber constructed in the present study.

A theoretical study on accurate measurements of thoron with airflow-through scintillation cell method

For accurate measurements of (220)Rn concentration with airflow-through scintillation cell method, a theoretical study was performed for discussing the influences of sampling flow rate, volumes of sampling tube and scintillation cell on the measurements. It is found that a high flow rate and a large inner volume of scintillation cell as well as a small inner volume of sampling tube are not only preferable for measuring low levels of (220)Rn, but also helpful for enhancing the measurement accuracy. In calibration experiments, both the sampling flow rate and the sampling tube volume should be noted. The variations of the flow rate and tube volume should be considered for accurate measurements in the fields.

Quality assurance and quality control for thoron measurement at NIRS

The National Institute of Radiological Sciences (NIRS) has developed passive radon ((222)Rn)-thoron ((220)Rn) discriminative detectors for a large-scale survey and has established a thoron chamber to calibrate such detectors. In order to establish quality assurance and quality control for the (220)Rn measurement at NIRS, intercomparison studies have been carried out. The intercomparisons using a scintillation cell method, which has been used as a standard for (220)Rn measurement at NIRS, were conducted at New York University (NYU, USA) and Physikalisch-Technische Bundesanstalt (PTB, Germany). As a result, it was found that the result from the NIRS was in good agreement with that from the NYU. On the other hand, it was observed that the relative discrepancy between the (220)Rn concentrations from the NIRS and PTB monitors was, on average, >50 %. Using the NIRS (220)Rn chamber, the international intercomparison experiment for passive (220)Rn detectors started in 2008.

Solid thoron source preparation in a porous mineral matrix

Thoron and progeny are decay products of (232)Th with a great impact on human health. The release of thoron gas from the mining and milling of thorite, monazite and other major thorium ores has been recognised as a potential radiological health hazard. For precise measurements, calibration is a very important factor. This paper describes a cheap and easy way of producing a stable thoron source made of thorium nitrate packed in a porous clay mineral matrix used as (220)Rn generator. The source should have a small spherical shape and be fired at 600°C; this will lead to a great pore volume, necessary for the thoron gas. High importance should be given to the water uptake. The exhalation power of (220)Rn was measured using a Lucas scintillation cell. Experimental efficiency values obtained ranged between 0.16 and 1.44 %.

Measurement of thoron gas in the environment using a Lucas scintillation cell

A simple and fast method for measuring the concentration of 220Rn in the environment was developed based on the AB-5 portable radon measuring device.First, background counts were measured with a Lucas scintillation cell (LSC), thenair sampling measurement was started immediately and lasted for 1 min; the 220Rn concentration could be calculated from the counts before and after sampling as well as thetheoretical detection efficiency. Results of theoretical calculations showed that in a pure 220Rn environment the lower detection limit of the LSC would be some 65 Bq m−3 (with aconfidence level of 70%). The experimental results showed that compared with a RAD7 monitor in pure 220Rn or mixed 222Rn/220Rn environments thedeviations were less than ± 10%. This method can also be used for quantitative measurement of 220Rn concentration.

A simple technique for studying the dependence of radon and thoron exhalation rate from building materials on absolute humidity

Indoor radon and thoron concentrations were dominated with their exhalation rate from building materials. Thus, the evaluation of exhalation rate with highly precise is important. This paper presented a new technique to measure the dependence radon/thoron exhalation rate, from building materials used in Japan, on absolute humidity. The measurement technique consisted of a solid state alpha detector equipped a ventilation-type chamber and humidity control system in a flow through method. The exhalation rate of dried samples (Indian red granite and Japanese gray granite) was measured at various absolute humidity levels in the range of 1–20 g cm−3. It was found that exhalation rate increased exponential with increasing of absolute humidity for both samples. Furthermore, the dependence of radon emanation coefficient on building material’s temperature was also studied using an accumulation chamber equipped with scintillation cell alpha detector. The emanation coefficient of dry sample increased proportionally with increasing the material’s temperature with a correlation factor of 0.88.

An efficient and simple method for measuring 226Ra using the scintillation cell in a delayed coincidence counting system (RaDeCC)

A delayed coincidence counter (RaDeCC), developed to determine ultra-low levels of 223Ra (half life = 11.1 days) and 224Ra (half life = 3.6 days) in seawater, was adapted to measure 226Ra (half life = 1622 years). After pre-concentration of Ra from seawater onto MnO 2-coated fiber we show in this study that the 226Ra activity can be determined using the RaDeCC's ability to record alpha decay of its daughters as total counts. For sufficient ingrowth of 222Rn, the Mn-fiber is hermetically sealed in a column for a few days. Then, the ingrown 222Rn is circulated through the RaDeCC air-loop system followed by shutting down of the pump and closure of the scintillation cell for equilibration. Counting may be completed within a few hours for seawater samples. Sample measurements with this method agreed well with data obtained using gamma-ray spectrometry. This proves that a set of Ra isotopes ( 223Ra, 224Ra, and 226Ra), commonly used for geophysical studies such as mixing rates of different water masses and submarine groundwater discharge, can be efficiently and rapidly measured using the RaDeCC.

Comparison of various methods of estimating radon dose at underground workplaces in wineries

Levels of radon were surveyed in the air at underground workplaces of eight major Slovenian wineries. Geometric mean and geometric standard deviation values, respectively, obtained with different devices were 81 Bq m(-3) and 2.3 with alpha scintillation cells, 114 Bq m(-3) and 2.0 by exposing etched track detectors for 1-5 months, and 183 Bq m(-3) and 2.6 from 1-4-weeks continuous measurements. The equilibrium factor was 0.25-0.67, and the unattached fraction of radon short-lived decay products was in the range 0.09-0.20. Effective doses were calculated and compared based on radon data obtained with different techniques.

Radon measurement uncertainty: Comparison between passive short-term and active measurement

The measurement of indoor 222Rn is not as straightforward as commonly perceived. The most commonly used measurement method is a passive, short-term device using activated charcoal that collects gases, typically for 3–7 days. Short-term measurements are popular because a radon determination is often required by a homebuyer and the buying transaction needs to be completed within 30–60 days. From deployment to obtaining the result from a laboratory reading the passive short-term device can take about 2 weeks. Active measurements, in which a portable alpha-particle counter is placed within a house and air pumped through a scintillation cell have been compared to passive short-term measurements and found to be consistent. For transactions requiring faster or immediate results, active counting methods appear to be a reliable method for measurement.

Exposure to radon in the Gadime Cave, Kosovo

Air radon concentration was measured in summer and winter at 11 points along the tourist guided route in the Gadime Cave in Kosovo using alpha scintillation cells and etched track detectors. At two points in summer, values higher than 1700 Bq m −3 were observed; they otherwise were in the range 400–1000 Bq m −3. Values were lower in winter. The effective dose received by a person during a 90 min visit is 3.7 μSv in summer and 2.5 μSv in winter. For a tourist guide the annual effective dose is less than 3.5 mSv.

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.

Fifteen years experience in measuring 224Ra and 223Ra by delayed-coincidence counting

The RaDeCC™ system has proved to be a robust method of measuring 223Ra and 224Ra extracted from natural waters. Samples ranging in size from < 1 to > 1000 L are first concentrated onto Mn-fiber. The Mn-fiber is partially dried and placed into a circulation system with helium as the carrier gas. Alpha decays of the radon daughters of 223Ra and 224Ra are recorded in a scintillation cell. These data are used to activate electronic gates in the delayed coincidence system, which separate events due to 223Ra from those due to 224Ra. The system combines a high detection efficiency with low background to accurately measure 223Ra and 224Ra at concentrations on the order of 5 atoms per liter. Since this system was first deployed, numerous improvements in electronics and technique have occurred. In this paper I present tests we have conducted to confirm certain assumptions and improve the overall technique of sample collection and measurement.

A novel methodology for online measurement of thoron using Lucas scintillation cell

The use of Lucas scintillation cell (LSC) technique for thoron estimation requires a modified methodology as opposed to radon estimation. While in the latter, the α counting is performed after a delay period varying between few hours to few days, in the case of thoron estimation the α counting has to be carried out immediately after sampling owing to the short half-life of thoron (55s). This can be achieved best by having an on-line LSC sampling and counting system. However, half-life of the thoron decay product 212Pb being 10.6h, the background accumulates in LSC during online measurements and hence subsequent use of LSC is erroneous unless normal background level is achieved in the cell. This problem can be circumvented by correcting for the average background counts accumulated during the counting period which may be theoretically estimated. In this study, a methodology has been developed to estimate the true counts due to thoron. A linear regression between the counts obtained experimentally and the fractional decay in regular intervals of time is used to obtain the actual thoron concentration. The novelty of this approach is that the background of the cell is automatically estimated as the intercept of the regression graph. The results obtained by this technique compare well with the two filter method and the thoron concentration produced from a standard thoron source. However, the LSC as such cannot be used for environmental samples because the minimum detection level is comparable with that of thoron concentrations prevailing in normal atmosphere.

Seasonal variation of indoor air radon concentration in schools in Kosovo

Indoor air radon ( Rn 222 ) concentrations were measured in March, May, August and December in 15 rooms of five elementary and in six rooms of one high school in Sharr, Kosovo, using alpha scintillation cells. Only in one room did the value exceed 200 Bq m - 3 . Values decreased from December to August, and from basement to first floor.

Calibration of a 220Rn flow-through source

Two reference methods have been established to calibrate the yield of a self-made 220Rn flow-through source. These reference methods include (a) a small scintillation cell flow-through method and (b) a gamma spectrometry method that takes advantage of an activated charcoal. The methods were validated theoretically and experimentally including intercomparison measurements. It is shown that the source is stable with a relative deviation less than 2.5% over 5 years, when the relative humidity ranged from 50 to 90%, and the temperature from 5 to 38 degrees C. The 220Rn monitor used in these reference methods is calibrated without a 220Rn gas source with determinate yield. On the basis of the calibration of the 220Rn source by the methods mentioned above, the accurate calibration of any 220Rn monitor by the self-made 220Rn source with stable yield is feasible.

Indoor air radon concentration in schools in Prizren, Kosovo

Indoor air radon ((222)Rn) concentrations were measured in spring and winter in 30 rooms of 9 elementary schools and 19 rooms of 6 high schools in Prizren, Kosovo, using alpha scintillation cells. Only in three rooms of elementary schools and four rooms of high schools did winter concentrations exceed 400 Bq m(-3).

Radon survey and exposure assessment in hospitals

In this study radon (222Rn) in indoor air was surveyed in 201 rooms of 26 major hospitals in Slovenia and annual effective doses for 1025 persons working in the rooms surveyed were estimated. Instantaneous radon concentrations were measured with alpha scintillation cells, long-term average concentrations with etched track detectors and electret detectors, and radon, its progeny and equilibrium factor were continuously recorded with portable devices. Effective doses were estimated by using ICRP Publication 65 methodology. Only in seven rooms did the average radon concentration, obtained by 1 month exposing etched track detectors, exceed the national limit of 400 Bq m-3; and these places will be mitigated; elsewhere it was lower. Annual effective doses for 966 persons (94.2%) were estimated as <1 mSv, but for 10 persons they were between 2.1 and 7.3 mSv. The results warn that in an environment with generally low radon levels, 'hot' points may be found, and therefore radon surveys should be carefully designed and performed in order not to miss them.

Calibration of an electrostatic chamber for thoron measurements in exhaled breath

An electrostatic chamber system used for measuring thoron in the exhaled breath of thorium workers is calibrated using a standard thoron source and a scintillation cell counting system. A formulation based on both a streamlined flow model and a well-mixed flow model in the chamber has been made to estimate thoron concentration in breath from the observed alpha counts. The experimental measurements of the ratio of the outlet and the inlet thoron concentrations across the chamber strongly validate the well-mixed flow model for thoron, as against the streamlined flow model. The progeny collection efficiency on the electrode has been found to be 70%. The study points out a major error by a factor of approximately 25 in the calibration factor reported in an earlier work. From the present study, the minimum detectable limit of the activity of (224)Ra, freely emanating thoron at mouth works out to be 0.36 Bq as against 0.014 Bq reported earlier for the same system.

Miners' exposure to radon and its decay products in some Iranian non-uranium underground mines

Measurements of radon, radon decay products and gamma exposure rate in 12 non-uranium underground mines have been carried out in order to estimate the occupational radiation exposure of miners. Continuous measurements of radon using pulse ionisation chambers and scintillation cell techniques were employed for these studies. Progenies of radon were collected on filter paper, and then a three-count procedure was used for the measurement. The equilibrium state between radon and its decay products has been determined. Concentrations of natural radionuclides ((226)Ra, (232)Th and (40)K) in ore and soil samples taken from various locations in each mine have been measured using a Canberra High Purity Germanium detector. Based on these measurements two ranges of dose were evident. Doses ranged from 0.1 to 1.52 mSv y(-1) for nine mines and from 10 to 31 mSv y(-1) for the other three mines. A separate grouping of the mines was recognised from radon concentrations, which varied from 2 Bq m(-3) to 10 kBq m(-3). In three of these mines, working level (WL) concentrations of the order of 36-1771 mWL were determined in different working areas. In all other mines, the concentrations were observed to be <45 mWL.