Scintillation Cell Research Articles

Systematic indoor radon and gamma-ray measurements in Slovenian schools.

During the winter months of 1992/93 and 1993/94, instantaneous indoor radon concentrations and gamma dose rates were measured in 890 schools in Slovenia attended in total by about 280,000 pupils. Under "closed conditions," the room to be surveyed was closed for more than 12 h prior to sampling, the air was sampled into alpha scintillation cells with a volume of 700 cm3, and alpha activity was measured. An arithmetic mean of 168 Bq m(-3) and a geometric mean of 82 Bq m(-3) were obtained. In 67% of schools, indoor radon concentrations were below 100 Bq m(-3), and in 8.7% (77 schools with about 16,000 pupils) they exceeded 400 Bq m(-3), which is the proposed Slovene action level. In the majority of cases, radon concentrations were high due to the geological characteristics of the ground. Approximately 70% of schools with high radon levels were found in the Karst region. Gamma dose rates were measured using a portable scintillation counter. An arithmetic mean of 102 nGy h(-1) and a geometric mean of 95 nGy h(-1) were obtained. No extraordinarily high values were recorded.

RADON PROGENY DEPOSITION STUDIES IN STATIC AND AC FIELDS USING A MODIFIED SCINTILLATION CELL AND ITS APPLICATIONS

Theoretical and experimental studies have been made on radon progeny deposition enhancements in static and AC electric fields in a stagnant environment using a modified cylindrical scintillation cell. It consists of a wire coated with zinc sulphide as a central electrode to which the electric fields are applied and the alpha scintillations due to radon and its progeny present in the cell are recorded by a Photo-Multiplier assembly. A generalised approach based on average volumetric displacements of charged particles across equipotential surfaces is presented for calculating the deposition fractions in the presence of static and AC fields. From this, formulae have been derived relating the observed count rates and the enhancement factors (EF) to the applied potential, progeny mobility and the charge lifetimes. The formulae for the case with AC field predict a linear variation of EF with the applied potential, regardless of the charge neutralization rate. Measurements of EF carried out with AC fields in 100% humid air containing radon, although limited to a range of 50–240 V (rms), confirm the validity of the linear enhancement theory. From the slope of this line, and the variations of EF observed in static field experiments, a mobility of 1.14±0.2 cm 2 V -1 s -1 and a charge lifetime of 0.014±0.002 s was obtained by fitting with the theoretical formulae. As these values are in reasonable agreement with the earlier values obtained by spectrometric methods, it demonstrates the use of AC field techniques for these estimations, in stagnant air. Application of this technique for these studies under different environmental conditions, is suggested.

Efficiency of a large size scintillation cell

A large volume scintillation cell has been designed to detect low levels of radon and its progeny. The cell has a cylindrical shape (nominal volume 1.2 liters) with two photomultiplier tubes. In this study, the detection efficiency was estimated with Monte-Carlo calculations for 3-dimensional before fabrication. Counting efficiencies for241Am were measured along the axial of the cell with different distances between the source and the scintillation screen to confirm the calculation method. The counting efficiencies for the alpha particles from the226Rn and its short-live progenies were measured using a radon generator. The efficiency was estimated to be 0.36 count per alpha-particle as the average of three alpha-particles.

Radioactivity contents in building materials used in Hong Kong

The radioactivity contents in building materials used in Hong Kong were measured to determine the sources of the high indoor radon concentrations observed in local buildings. The radium contents and the radon emanation coefficients of different building materials were measured by high resolution γ-ray spectroscopy using germanium detectors. The radon exhalation rates were measured using scintillation cells by circulating the exhaled radon from building materials and obtaining the initial growth rates. The radium content and the radon exhalation rates of concrete and bricks used in Hong Kong were found to be higher than those in some other countries, resulting in high indoor radon concentrations probably due to the high radioactivity contents in the aggregates, granitic in nature, used in building materials.

Simple on-line monitoring of α- and β-emitters by solid scintillation counting

We prepared a solid scintillation cell by vortexing a molten plastic scintillator at 195°C through a heat-resistant plastic tube. The cell was adapted to commercially available counting equipment and used for on-line monitoring and tested with high-level waste components such as Sr/Y-90, Ru/Rh-106, Sb-125, Cs-134, Pm-147, U-233, Am-241 and Cm-244. We obtained perfectly linear calibration curves and determined the detection limits to be in the range of 0.5–70 Bq per sample or 1–40 Bq ml −1 for β-emitters and 50 Bq per sample or 35 Bq ml −1 for α-emitters. The α-detection limits can be reduced to 10 Bq ml −1 by setting energy windows. Due to the minimal pressure loss and lack of scintillation contaminants in the cell effluent, the cell can be employed for monitoring processes on an analytical as well as on a technical scale. Although the detector was originally designed for gross α- and β-counting, even high-energetic β-emission can be partially suppressed by choosing the appropriate energy range and varying the cell geometry.

A Survey of Radon‐222 in Ground Water from the Sherwood Sandstone Aquifer: Belfast and Newtownards, Northern Ireland

AbstractA study of radon‐222 in ground water in Northern Ireland has revealed a range of concentrations from 5.8Bql−1 to 36.6Bql−1 (158pCil−1 (158pCil−1 to 989 pCil−1). Radon‐222 was measured using a portable degassing system with scintillation cells and a portable radiation detector. Twenty‐six samples were taken within the Sherwood Sandstone Aquifer underlying Belfast and Newtownards, County Down.; All samples collected were below the National Radiological Protection Board (NRPB) suggested limit of 100Bql−1. Several hypotheses were considered for the distribution pattern in the sandstone, the most probable being the presence of faults and lithological differences.

Experimental study of radon and thoron diffusion through barriers

The radon chamber and radon calibration set have been modified for investigation of the diffusion coefficients of the barriers for reduction of radon exposure in the dwellings and for application as filters to separate radon and thoron. The volume radon activities have been measured by continuous monitors with scintillation cell or ionisation chamber. The theory on which the experimental determination of a barrier diffusion coefficient is based, is presented. The diffusion ability of radon has been studied for different materials and the results of the measurements are presented and discussed.

A Fast Portable Emanometer for Field Measurement of Radon and Thoron Flux

A new emanometer for measurement of 222Rn (radon) and 220Rn (thoron) flux density, based on the flow-through accumulator method is presented. The radon and thoron buildup is measured, and the separation of their respective signals is achieved in a detection unit which consists of two scintillation cells connected in series with a delay volume between them. An emanometer model is developed to relate the flux densities to design parameters of the instrument. Limitations of the model are discussed. The lower limit of detection (at 30% relative standard error) for a 24 min. counting period is about 4 x 103Bq.m-2.s-1 and 4 x 10-2Bq.m-2.2-1 for radon and thoron, respectively. Better lower limits of detection can be achieved by using longer counting times. The relative merits of closed and flow-through designs are discussed.

A pulse-coincidence 220Rn monitor with three time-gates

A pulse-coincidence 220Rn monitor has been developed for low-level continuous measurement. This method is based on delayed coincidences between the alpha pulses of 220Rn and 216Po. The monitor consists of a 300-mL flow-through scintillation cell facing a photomultiplier tube, connected to a custom-built pulse-coincidence circuit with three time-gates to distinguish 220Rn- 216Po pairs counts from sequential alpha pulses. Each time-gate has an open duration time of 150, 300, or 450 ms, respectively. The output of the time-gates is used in statistical analysis to ascertain that the real 220Rn- 216Po pair counts are correctly discriminated. Poisson distribution probability is introduced to correct for chance coincidence pulses. The sensitivity of the monitor is estimated at about 0.58 cph/Bq m −3 for 220Rn where cph is counts per hour. Therefore, this monitor is particularly useful for a low-level concentration. In addition, another data analysis method is also suggested for utilization of this monitor in high-level environments. The quality of 220Rn concentration estimated by the monitor is guaranteed by a comparison with the value of a grab sampling method using a scintillation cell.

A Fast and Accurate Radon Measurement Tool for Remedial Actions in Buildings

Abstract Continuous monitoring of radon concentration is an effective and fast method for assessing radon sources in buildings. For this purpose, fast response and absence of residual contribution from previous measurements is of primary importance to cut intervention time and cost in a remedial action. An instrument is described based on a scintillation cell. Counts from the detection assembly are processed by a microprocessor-based unit in order to compensate plateout and thus shorten the detector response step down to 15 min compared to the typical 3 h. A new treatment of the cell background, added to the algorithms, cancels the detector memory of previous measurements. The instrument has the ability to characterise both high and low activity environments in rapid sequence, even with a switch off/on operation in between, with almost no influence on the measure accuracy. A discussion of the computations and results from measurements is given.

A Fast and Accurate Radon Measurement Tool for Remedial Actions in Buildings

Continuous monitoring of radon concentration is an effective and fast method for assessing radon sources in buildings. For this purpose, fast response and absence of residual contribution from previous measurements is of primary importance to cut intervention time and cost in a remedial action. An instrument is described based on a scintillation cell. Counts from the detection assembly are processed by a microprocessor-based unit in order to compensate plateout and thus shorten the detector response step down to 15 min compared to the typical 3 h. A new treatment of the cell background, added to the algorithms, cancels the detector memory of previous measurements. The instrument has the ability to characterise both high and low activity environments in rapid sequence, even with a switch off/on operation in between, with almost no influence on the measure accuracy. A discussion of the computations and results from measurements is given.

Efficiency of the Lucas scintillation cell

The Lucas scintillation cell (LC) and its modifications are among the most sensitive instruments to detect low levels of radon. In this work we describe a comprehensive investigation of the counting efficiency of the LC. A known quantity of 222Rn was transferred into the LC and the decay and ingrowth of Rn and its daughters was followed in an automated measurement with counting intervals ranging from 5 s to 12 h. A total of 7014 measurements were taken in a period exceeding 5 months. The measurements taken during Rn transfer to the LC indicated that the separation was not ideal and that small amounts of daughters were also transferred to the LC. A numerical model was then developed and fitted to the data. The model includes kinetics of Rn transfer to the LC, a matrix-algebra method for description of decay and growth of Rn and its daughters, individual counting efficiencies, as well as several small corrections. Individual α counting efficiencies (counts/particle) were determined: 0.76(2) for 222Rn, 0.77(3) for 218Po, 0.91(1) for 214Po, and 0.8283(6) for 210Po. A contribution from electrons to the efficiency was found to be insignificant. The work is concluded by providing an overall counting efficiency of LC as a function of decay and counting times, which is of practical interest to radon measurements.

Design, calibration, and operation of 220Rn stack effluent monitoring systems at Argonne National Laboratory.

A group of stack effluent monitoring systems have been developed to monitor discharges of 220Rn from a hot cell facility at Argonne National Laboratory. The stack monitors use flow-through scintillation cells and are completely microprocessor-based systems. A method for calibrating the stack monitors in the laboratory and in the field is described. A nominal calibration factor for the stack monitoring systems in use is 15.0 cts min-1 per kBq m-3 (0.56 cts min-1 per pCi L-1) +/- 26% at the 95% confidence level. The plate-out fraction of decay products in the stack monitor scintillation cells, without any pre-filtering, was found to be nominally 25% under normal operating conditions. When the sample was pre-filtered upstream of the scintillation cell, the observed cell plate-out fraction ranged from 16-22%, depending on the specific sampling conditions. The instantaneous 220Rn stack concentration can be underestimated or overestimated when the steady state condition established between 220Rn and its decay products in the scintillation cell is disrupted by sudden changes in the monitored 220Rn concentration. For long-term measurements, however, the time-averaged response of the monitor represents the steady state condition and leads to a reasonable estimate of the average 220Rn concentration during the monitoring period.

Radon distribution in dwellings

Radon concentrations inside a flat were measured with a Radhome semiconductor detector and scintillation cells. An unusual radon distribution was noticed within one room as well as in the basement. An anomalous distribution of the radon in the single house, where the radon concentration of the basement was a factor of 4 lower than that of the first floor for a few days, was explained by variations in the atmospheric pressure. Radon measurements inside a high building did not show any significant difference for various floors, but outdoor radon concentrations on open balconies indicated an exponential decrease of radon concentration in the atmosphere with altitude.

An instrument for continuous measurement of 220Rn (and 222Rn) using delayed coincidences between 220Rn and 216Po

An instrument has been developed for continuous monitoring of 220Rn. The method of data analysis is based on delayed coincidences between 220Rn and 216Po. The instrument basically consists of a scaler equipped with a photomultiplier tube (PMT) to which a scintillation cell (SC) of the flow through type is optically coupled. The scaler is equipped with a pulse output (P/O) port which provides a TTL pulse, +5 V in amplitude and 5 to 10 μs duration for each nuclear event recorded by the SC and its associated electronic circuitry. The P/O port is connected to a 32 bit counter/timer unit operating at 1 MHz which records and stores the time of arrival of pulses. For laboratory use, the counter/timer is connected to the serial port of a laptop PC. However, for field applications, where space and weight pose severe practical limitations, the PC is substituted by an expanded counter/timer unit which incorporates a muprocessor for data analysis, a LCD for data display, and a keypad to key in function instructions. Furthermore, some additional hardware permits the measurement of 220Rn flux density, J( 220 Rn) , from soils and other materials. Because total α-particle count, as well as delayed (α - α) coincidence rates are recorded in two separate channels, the method permits the measurement of 222Rn in addition to 220Rn. The method is particularly useful for low concentration levels. The sensitivity of the method primarily depends on the volume of the SC. For a low volume SC (∼0.16 l), a sensitivity of 0.2 h −1/Bq m −3 for 220Rn and 1.4 h −1/Bq m −3 for 222Rn are readily attainable. For a large volume (1.5 l) SC (external PMT used), the sensitivity for 220Rn is ≥ 1.5 h −1/Bq m −3, depending on the SC design and the operating sampling flowrate. (Note: h −1 stands for counts per hour). The above instrument has been used extensively at the National Radon/Thoron Test Facility (NRTTF) of the Elliot Lake Laboratory for routine monitoring of 220Rn levels since 1992. It has also been used for outdoor and indoor 220Rn measurements, as well as for the determination of J( 220 Rn) from earthen materials and the like.

Systematic indoor radon and gamma measurements in kindergartens and play schools in Slovenia.

Systematic measurements of indoor radon concentrations and gamma dose rates were carried out in the 730 kindergartens and play schools in Slovenia that, together, care for 65,600 children. The main method for indoor radon measurement was direct sampling in alpha scintillation cells, but in cases with an increased instantaneous radon concentration, the additional methods of track-etch detectors and alpha spectroscopy were applied. In 528 kindergartens and play schools (72%), radon concentrations were below 100 Bq m-3, with a geometric mean of 58 Bq m-3. In 16 kindergartens and play schools (2.2%), radon concentrations exceeded 800 Bq m-3. In all cases, the main reason for a high indoor radon concentration was the geological structure of the soil. Gamma dose rates were measured with a portable scintillation counter, but in the Ljubljana region thermoluminescence dosimeters were also exposed. The results ranged from 30 to 295 nGy h-1, with a geometric mean of 88 nGy h-1.

Improved 220Rn measurement characteristics of scintillation cells cooled to liquid nitrogen temperatures

The 220Rn α-particle counting characteristics of a ZnS(Ag) scintillation cell cooled to liquid nitrogen (LN2) temperatures have been investigated. The cell was designed to serve a dual purpose, namely, to operate as a cold trap (when cooled at LN2) to condense 220Rn flowing through a counting system of the flow through type, and as an efficient α-particle detector. An improvement in the counting rate of 50 to ∼ 100% has been observed when compared with a similar system operating at room temperature. It is possible to improve the characteristics of the system significantly by careful redesign of the geometry of the scintillation cell, i.e. by machining the cell in a semi-spherical shape, and reducing its physical dimensions to equal or less than the range of the α-particles from the decay of 220Rn.

Preliminary Indoor Radon Investigations in Lublin Region, Poland

Indoor air radon concentrations in all kindergartens and play schools in Lublin, Poland, were determined in grab samples by using alpha scintillation cells. In addition, some public buildings and homes in Lublin and several places in Eastern Poland were surveyed for radon. For kindergartens and play schools, the geometric mean was 23 Bq m-3 with a standard deviation of 1.4 Bq m-3, while in public buildings and homes, these values were 26 and 1.6 Bq m-3, respectively.

Statistical uncertainties associated with multiplexed sampling with a continuous radon monitor.

One common type of continuous radon monitor is a flow-through device that counts alpha emissions from a gas sample as it passes through a scintillation cell. To improve the ability of this type of continuous radon monitor to track time-varying radon concentrations, a forward-marching data analysis procedure that considers the production, deposition, and decay of radon progeny as a function of time had been previously developed. This paper examines some of the statistical issues associated with using such a monitor and applying the forward-marching analysis procedure to the problem of multiplexed radon concentration samples. It uses Monte Carlo simulations, together with limited experimental data, to perform: 1) an examination of the potential bias of the forward-marching analysis technique; 2) an examination of a simplified methodology for evaluating concentration-measurement uncertainty for various radon concentration histories; and 3) an analysis of an example application of the simplified uncertainty analysis to multiplexing of soil-gas samples. The results of these analyses indicate: 1) that the forward-marching analysis technique is relatively unbiased, at least at concentrations > 148 Bq m-3 for time steps longer than 120 s; 2) that a simplified uncertainty analysis procedure based upon Poisson statistics and no error correlation between intervals provides generally acceptable estimates of measurement uncertainty; and 3) that such a monitor and analysis technique can be successfully employed to measure multiplexed soil-gas samples, but is not appropriate for multiplexing of most building concentrations.

Radon concentrations in kindergartens of Osijek and Ljubljana

Indoor radon concentrations in the kidergartens of Osijek, Croatia, have been measured with α-scintillation cells, LR-115 nuclear track detectors, as well as a Radhome semiconductor detector. Average values of 50.2, 43.7 and 47 Bq m−3 were obtained, respectively. Under the worst conditions, the annual radon effective dose equivalent was 10 mSv y−1. Using bare and filtered LR-115 detectors, the average equilibrium factor was assessed as 0.36 indoors. Measurements of the γ-dose rate in the kindergartens did not show any significant correlation with the radon concentration. Indoor radon concentrations in the kindergartens of Ljubljana, Slovenia, measured by scintillation cells had an arithmetic mean and standard deviation of 228 and 143 Bq m−3, respectively.