Electret Ion Chambers Research Articles

Influences on indoor radon concentrations in Riyadh, Saudi Arabia

The influences on indoor radon concentrations in Riyadh, Saudi Arabia survey was carried out for 786 dwellings. The measurements were obtained by using a passive integrating ionization system with an E-Perm® Electret ion chamber. Radon levels ranged from 1 to 195 Bq m−3, with a mean value of 24.68 Bq m−3, the geometric mean and the geometric standard deviation are 21 and 2 respectively. 98.5% of the results were below the action level recommended by WHO of 100 Bq.m−3. The results were found to vary substantially due to types of houses and rooms, ventilation, seasons and building materials. Radon concentrations were higher in houses with no ventilation systems, and central air conditioners, and were relatively lower in well ventilated houses with red bricks and water air conditioners.

Radiation exposure related to the shipment of fertilisers to and from commercial ports: the case study of the seaport of Ravenna (Italy)

This paper presents the results of a study of radiological impacts related to the shipment of fertilisers to and from the commercial port of Ravenna (NE Italy). In particular, the effective doses to the port workers and members of the population surrounding the port area have been estimated. The study has included different types of measurement and assessment. First, the natural radioactivity of different fertilisers moving through the port has been determined: 40K, 226Ra, 210Pb, 228Ra and 228Th concentrations have been analysed using γ-ray spectrometry, while 238U and 232Th concentrations have been determined by ICP-MS. At the same time, a dose rate meter and electret ion chambers were used to measure the external irradiation and the radon concentrations, respectively. Then, air pollutant dispersion models have been applied in order to assess particulate matter concentration in the port site and the surrounding residential areas, and consequently the inhalation doses. Finally, the annual effective doses to workers and local residents have been estimated. The effective doses to workers and the population have been estimated to be 0.9 mSv yr−1 and 0.07 μSv yr−1, respectively.

Assessment of indoor radon concentration in phosphate fertilizer warehouses in Nigeria

Indoor radon concentration level was measured in twelve selected phosphate fertilizer warehouses in Nigeria in order to establish potential hazards to persons using such warehouses as offices. The fertilizer warehouses were selected based on the brand of fertilizers stored, size, ventilation pattern and the number of workers in the warehouses during working hours. Electret Ion Chamber Technology (EIC) with the trade name E-PERM TM was employed for the measurement of radon concentration in the warehouses. Average radon concentration in the warehouses range between 33.6 Bq m −3 and 117 Bq m −3with an arithmetic mean of 91.62±5.9 Bq m −3.

Statistical model of quality of radon measurements using electret ion chamber detectors

This paper presents a statistical model for estimating probability, which states that a quality of radon measurements using the electret ion chamber system RM-1 will be accurate. The quality of the electret measurement was modelled as a ratio between the reference radon concentration and values measured under real conditions with varied levels of indoor radon concentration and microclimate indoor conditions. It was stated that the accuracy tolerance of measured values is 20 % of the given reference value. To estimate the uncertainty of the statistical model, the exact confidence limits for the estimated probabilities are computed. The statistical model was confirmed by an independent set of measurements. Moreover, the effect of absolute humidity on the quality estimation of electret detectors are also statistically analysed and discussed. The results of the statistical model confirm that the electret system is robust and suitable for estimation of radon concentration.

Discharge of ferroelectrets upon ionizing alpha-radiation

Ferroelectrets, with their internal bipolar charges on the surfaces of the voids can be viewed as a collection of a large number of individual tiny electret ionization chambers. Electrets in ionization chambers are discharged upon irradiation with ionizing radiation. The discharge of cellular propylene is studied upon irradiation with alpha-radiation from a 226Ra source, while in-situ measuring the piezoelectric effect. Piezoelectric coefficients are derived from piezoelectric thickness extension resonances and from the second harmonic current upon application of a sinusoidal voltage signal. The piezoelectric coefficient gives a direct measure of the effective internal surface charge density within the voids of the cellular material. Compared to electret ionizing chambers, a much better temporal stability of charges in ferroelectrets is observed. The small air volume in the voids of cellular polypropylene is believed to account for the remarkable charge stability.

Electret ion chamber-based passive radon-thoron discriminative monitors

Electret ion chambers (EICs), commercially available under brand name E-PERM(®), are widely used for measuring indoor and outdoor (222)Rn concentrations in air. These are designed to respond only to (222)Rn and not to (220)Rn by restricting diffusional entry area. Such radon EIC (R EIC) monitors are modified by increasing the entry area to allow (220)Rn, in addition to (222)Rn. Such modified units are called RT EIC. When a set of R and RT EICs are collocated, it is possible to discriminate and measure both radon and thoron concentrations, using appropriate calibration factors (CFs) and algorithms. The EICs come in different volumes, providing different sensitivities. The thoron CFs for 58-, 210- and 960-ml volume R and RT pairs are, respectively, 2.8-, 18.7- and 89-V drop per (kBq m(-3) d ), respectively. These provide much wider sensitivities and ranges compared to alpha track-based passive radon-thoron discriminative monitors.

A pilot study on natural radioactivity in schools of south-east Italy

In the period 2005–2006 a survey on natural radioactivity in about 500 schools located in south-east Italy (the Salento peninsula, province of Lecce) was carried out. In particular average radon concentration and average absorbed dose rate in air due to gamma radiation have been assessed by using solid state nuclear track detectors (SSNTD) and electret ionization chambers (EIC), as well as thermoluminescence dosimeters (TLD), respectively. SSNTD dosimeters were placed in every school, while electrets and TLD have been employed in a pilot study performed in a selected sample of 56 schools in order to achieve preliminary information. Moreover the study foresaw a quality control on electret dosimeters' perfomances in terms of homogeneity and reliability. The results of this check have been taken into account in the data analysis. In this paper final results concerning the pilot study are reported. The indoor radon levels measured in the schools ranged from 65 Bq/m 3 to 1808 Bq/m 3, and only six schools (corresponding to 13% of the sample) showed radon annual average above 500 Bq/m 3, Italian action level for workplaces. For the average absorbed dose rate in air due to gamma radiation, the recorded values ranged between 47 and 83 nGy/h with an average value of 61 nGy/h.

RADON EXHALATION RATES FROM BUILDING MATERIALS USING ELECTRET ION CHAMBER RADON MONITORS IN ACCUMULATORS

An electret ion chamber (EIC) radon monitor in a sealed accumulator measures the integrated average radon concentration at the end of the accumulation duration. Theoretical equations have been derived to relate such radon concentrations (Bq m(-3) ) to the radon emanation rate (Bq d(-1)) from building materials enclosed in the accumulator. As an illustration, a 4-L sealable glass jar has been used as an accumulator to calculate the radon emanation rate from different granite samples. The radon emanation rate was converted into radon flux (Bq mm(-2) d(-1)) by dividing the emanation rate by surface area of the sample. Fluxes measured on typical, commercially available granites ranged from 20-30 Bq m(-2) d(-1). These results are similar to the results reported in the literature. The lower limit of detection for a 2-d measurement works out to be 7 Bq m(-2) d(-1). Equations derived can also be used for other sealable accumulators and other integrating detectors, such as alpha track detectors.

Long term stability of electrets used in electret ion chambers

Commercially available electret ion chambers have been using electrets for more than 15 years. As a quality control procedure, a few electrets from each production batch are set aside for studying their long term stability. These are measured after storage of 1–13 years, to calculate the decay rates for different storage periods. Two types of electrets are studied. The first type is the Teflon ® electret made of PTFE Teflon ® (polytetrafluoroethylene) with a thickness of 1.524 mm and the second type is Teflon ® electret made of FEP Teflon ® (fluorinated ethylene propylene) with a thickness of 0.127 mm. In both cases, one side is carbon coated. The first type shows an average decay of about 4% per year. The second type shows an average decay rate of about 1% per year. The decay rate does not change significantly over the years of study. After accounting for decay due to ions in storage conditions, the half life (time required to decay by 50%) of 1.524 mm and 0.127 mm thick electrets is 14 and 68 years, respectively. Such unusually long half lives make the electrets useful for a number of practical applications where a high electrostatic field is needed over an extended period, without having to use batteries or high voltage sources.

LEAKAGE CORRECTION ESTIMATE FOR ELECTRET ION CHAMBER DIELECTRIC MATERIAL USED FOR LONG-TERM ENVIRONMENTAL GAMMA MONITORING

The Idaho Department of Environmental Quality INL Oversight Program (DEQ-INL) operates an environmental gamma radiation detection network consisting of a series of high-pressure ion chambers to provide real-time ambient radiation measurements and a series of passive environmental electret ion chambers to increase coverage area and measure cumulative dose over a calendar quarter. DEQ-INL has identified a consistent over-response of approximately 40% by the electret ion chambers with respect to co-located high-pressure ion chambers since 1998. DEQ-INL conducted a series of three investigations to quantify this over-response. The over-response is likely attributable to a number of factors, including inherent voltage loss by the electret material not due to ionization within the chamber. One aspect of the investigation verified the manufacturer's calibration factor used to convert decrease in voltage to exposure. Additional investigations were performed that identified an average electret voltage loss of 0.2 V d(-1). When this voltage correction was applied to historical environmental data, electret ion chamber response was within 10% of the co-located high-pressure ion chamber response.

Performance of a commercial radon-in-water measurement kit

Methods currently approved for the measurement of radon ( 222Rn) in water in New York State are liquid scintillation counting and emanation into alpha-scintillation cells. A passive system using an electret ion chamber (EIC) was evaluated as an alternative for the measurement of radon in water. Over 130 water samples from a community water supply containing 32 Bq L −1 and 30 standards containing 686 Bq L −1 were measured using the EIC method over 1- to 4-day exposure times. For comparison, identical samples were measured using liquid scintillation counting. Results of duplicate samples were typically within 5% for liquid scintillation counting and within 10% for the EIC. With respect to accuracy, the EIC produced results that were consistently low by 11–15%.

A study of airborne radon levels in Paarl houses (South Africa) and associated source terms, using electret ion chambers and gamma-ray spectrometry

Indoor radon ( 222Rn) concentrations were measured in Paarl homes by means of electret ion chambers. The concentrations varied between 28 and 465 Bq m −3. The average values (Bq m −3) found in houses on the west and east side of the Berg River, which bisects Paarl, were 132 (±11) and 37 (±3), respectively. Radiometric analyses of soils show that the mean 226Ra activity concentration is three times higher on the west than on the east side of the Berg River.

One cubic metre NIST traceable radon test chamber

With the availability of the National Institute of Standards and Technology (NIST) Radon Emanation Standard with a content of approximately 5000 Bq of 226Ra, it is possible to build a flow through a practical radon test chamber. A standard glove box with four gloves and a transfer port is used. Air is pumped through a flow integrator, water jar for humidification and NIST source holder, and into the glove box through a manifold. A derived theoretical expression provides the calculated radon concentration inside the chamber. The calculation includes a derived decay correction due to the large volume and low flow rate of the system. Several calibrated continuous radon monitors and passive integrating electret ion chambers tested in the chamber agreed fairly well with the calculated radon concentrations. The chamber is suitable for handling the calibration of several detectors at the same time.

RADON MEASUREMENT IN CANADA WITH ELECTRET ION CHAMBERS

Electret ion chambers are the most commonly used passive radon detectors. This paper discusses some practical issues associated with the use of electret ion chambers and provides background gamma correction factors for their use in Canada.

Measurement of the Concentration of Radon Gas in the Toirano's Caves (Liguria)

The radioactive gas radon, intermediate term of the decay series of uranium and thorium, is the main contamination source of underground places and may be a risk for high concentration and long exposure time. European and Italian law requires radon concentration to be measured in workplaces and, if the "action level" of 500 Bq/m3 is reached, proper actions must be made in order to decrease the dose commitment. Considering natural showcaves or artificial cavities open to public, the exposition of the visitors is frequently small, due to the short residence time, but accompanying people, remaining underground for long time, may be subject to appreciable dose and the radon concentration should therefore be monitored. The high humidity in natural caves may impair the use of some measuring devices. Therefore, different detection methods were compared (ZnS scintillation counters, E-PERM electret ionisation chambers, cellulose nitrate alpha-track dosimeters) to select the best procedure for long-term investigation. The LR-115 (Kodak) alpha-track dosimeters were insensitive to humidity and permitted to monitor a great number of places at the same time. Measurements have been carried out in the speleological and archaeological site of the Toirano's Caves (Savona, Liguria, Italy) and several points were monitored for two years. Radon concentration strongly depends on the site and changes during the year, due to the difference between internal and external temperature. The maximum dose commitment during the visitors tour, considering the average yearly value of radon concentration, was found to be between 1.5 and 4 microSv. It was found that no risk exists for visitors, but the evaluation of the dose absorbed by the guides and their classification according to the radiation protection law requires a complete monitoring of the average yearly concentration of radon and of the total time spent by each worker into the cave.

PERFORMANCE OF ELECTRET IONIZATION CHAMBERS IN MAGNETIC FIELD

Electret ionization chambers are widely used for measuring radon and radiation. The radiation measured includes alpha, beta, and gamma radiation. These detectors do not have any electronics and as such can be introduced into magnetic field regions. It is of interest to study the effect of magnetic fields on the performance of these detectors. Relative responses are measured with and without magnetic fields present. Quantitative responses are measured as the magnetic field is varied from 8 kA/m to 716 kA/m (100 to 9,000 gauss). No significant effect is observed for measuring alpha radiation and gamma radiation. However, a significant systematic effect is observed while measuring beta radiation from a 90Sr-Y source. Depending upon the field orientation, the relative response increased from 1.0 to 2.7 (vertical position) and decreased from 1.0 to 0.60 (horizontal position). This is explained as due to the setting up of a circular motion for the electrons by the magnetic field, which may increase or decrease the path length in air depending upon the experimental configuration. It is concluded that these ionization chambers can be used for measuring alpha (and hence radon) and gamma radiation in the range of magnetic fields studied. However, caution must be exercised if measuring beta radiation.

Simultaneous measurements of indoor radon, radon–thoron progeny and high-resolution gamma spectrometry in Greek dwellings

Simultaneous indoor radon, radon-thoron progeny and high-resolution in situ gamma spectrometry measurements, with portable high-purity Ge detector were performed in 26 dwellings of Thessaloniki, the second largest town of Greece, during March 2003-January 2005. The radon gas was measured with an AlphaGUARD ionisation chamber (in each of the 26 dwellings) every 10 min, for a time period between 7 and 10 d. Most of the values of radon gas concentration are between 20 and 30 Bq m(-3), with an arithmetic mean of 34 Bq m(-3). The maximum measured value of radon gas concentration is 516 Bq m(-3). The comparison between the radon gas measurements, performed with AlphaGUARD and short-term electret ionisation chamber, shows very good agreement, taking into account the relative short time period of the measurement and the relative low radon gas concentration. Radon and thoron progeny were measured with a SILENA (model 4s) instrument. From the radon and radon progeny measurements, the equilibrium factor F could be deduced. Most of the measurements of the equilibrium factor are within the range 0.4-0.5. The mean value of the equilibrium factor F is 0.49 +/- 0.10, i.e. close to the typical value of 0.4 adopted by UNSCEAR. The mean equilibrium equivalent thoron concentration measured in the 26 dwellings is EEC(thoron) = 1.38 +/- 0.79 Bq m(-3). The mean equilibrium equivalent thoron to radon ratio concentration, measured in the 26 dwellings, is 0.1 +/- 0.06. The mean total absorbed dose rate in air, owing to gamma radiation, is 58 +/- 12 nGy h(-1). The contribution of the different radionuclides to the total indoor gamma dose rate in air is 38% due to 40K, 36% due to thorium series and 26% due to uranium series. The annual effective dose, due to the different source terms (radon, thoron and external gamma radiation), is 1.05, 0.39 and 0.28 mSv, respectively.

Natural radioactivity and radon exhalation in building materials used in Italian dwellings

Forty-two samples of building materials commonly used in Italian dwellings were surveyed for natural radioactivity. External (gamma), as defined and used by the European Commission, and internal (alpha) hazard indexes were calculated and radon specific exhalation rate and emanation fraction were measured. The accumulation method, by using the E-PERM electret ion chambers, was employed to determine specific exhalation rates of 222Rn. Several of the materials had hazard indexes that exceeded the European Commission limit values. However, it was evident that limit values for internal hazard indexes set based on Rn emanation should take into account the properties and use of the materials. For example, Rn emanation from basalt and glazed tiles was substantially lower than the Rn emanation from other materials with similar hazard indexes. Clearly there is need for improved guidelines and regulations in this area.

Assessment of the radiological impacts of a zircon sand processing plant

The paper presents the results of a study on radiological impacts resulting from a zircon sand processing plant located in the North-Eastern part of Italy. Activity concentrations of radionuclides found in materials associated with this industrial process are presented as well as the results of the assessment of the annual effective doses to the workers and the members of the public. γ-Spectrometric analyses were performed on “raw” sands, end-products, and soils sampled near the plant. Thermoluminescent dosimeters, electric pumps and electret ion chambers were used to measure the external irradiation, the indoor dust concentrations and the radon concentrations, respectively. The ground-level air concentration of radioactive particulate near the plant and the deposition of particulate matter were estimated by a Gaussian model (ISCLT3). Finally, the annual effective doses, calculated as provided for by Directive 96/29/Euratom, were estimated to be 1.7 mSv y −1 for workers and 4.4 μSv y −1 for members of the public.

Uncertainties evaluation for electrets based devices used in radon detection

In recent years uncertainty evaluation in measurements has achieved great importance. National and international standards offer guidelines to evaluate uncertainties, but these procedures are, until now, not well understood by the operators. This is because of the fact that a detailed uncertainty evaluation is not an easy operation and a standard rule to apply in all cases is not available. Every measurement procedure has its own uncertainty evaluation. In this work, attention is focused upon the electret ion chambers (EIC), widely used in radon concentration measurements. Measurements of gamma radiation sensitivity are performed in a secondary standard calibration laboratory and measurement of radon concentration sensitivity is performed in a radon chamber 0.8 m3 in volume. Raw data are analysed to evaluate the calibration factors and the combined uncertainties are determined. The aim of the work is to give a practical method to assess the uncertainty of a radon measurement.