Electret Ion Chambers Research Articles

Response Comparisons of Electret Ion Chambers, LiF TLD, and HPIC

During each quarter of 1991 electret ion chambers, nat Lif, 6 LiF, and 7 LiF thermoluminescence dosemeters, all integrating ionising radiation monitors, were placed at a location in the grounds of the National Institute of Standards and Technology. One group was exposed to the total ambient field, while a second group was sealed for testing a method of protection against radon gas intrusion. A high-pressure ion chamber at the same location provided another measure of the field. Simultaneously with the environmental response test, other sealed and unsealed groups of electret ion chambers and thermoluminescence dosemeters were exposed during each quarter to discrete exposures from calibrated sources of 60 Co and 137 Cs. All responses were evaluated at the end of each quarter. The results indicated that the electret ion chamber gave results comparable to thermoluminescence dosemeters for routine environmental monitoring. No significant difference was found for any monitor type when sealed results were compared with unsealed results. The electret devices gave results that were, on the average, closer to the pressurised ion chamber results than did the thermoluminescence devices for both the sealed and unsealed sets for the ambient fields, and the electret devices also gave results closer to the delivered air kerma values than did the thermoluminescence devices in the deliberate exposure test. The electret ion chambers' responses showed a somewhat greater variability than did the thermoluminescence dosemeters' responses.

Calibration of Electret-Based Integral Radon Monitors Using NIST Polyethylene-Encapsulated 226Ra/222Rn Emanation (PERE) Standards.

The recently developed 222Rn emanation standards that are based on polyethylene-encapsulated 226Ra solutions were employed for a first field-measurement application test to demonstrate their efficacy in calibrating passive integral radon monitors. The performance of the capsules was evaluated with respect to the calibration needs of electret ionization chambers (E-PERM®, Rad Elec Inc.). The encapsulated standards emanate well-characterized and known quantities of 222Rn, and were used in two different-sized, relatively-small, accumulation vessels (about 3.6 L and 10 L) which also contained the deployed electret monitors under test. Calculated integral 222Rn activities from the capsules over various accumulation times were compared to the averaged electret responses. Evaluations were made with four encapsulated standards ranging in 226Ra activity from approximately 15 Bq to 540 Bq (with 222Rn emanation fractions of 0.888); over accumulation times from 1 d to 33 d; and with four different types of E-PERM detectors that were independently calibrated. The ratio of the electret chamber response ERn to the integral 222Rn activity IRn was constant (within statistical variations) over the variables of the specific capsule used, the accumulation volume, accumulation time, and detector type. The results clearly demonstrated the practicality and suitability of the encapsulated standards for providing a simple and readily-available calibration for those measurement applications. However, the mean ratio ERn/IRn was approximately 0.91, suggesting a possible systematic bias in the extant E-PERM calibrations. This 9 % systematic difference was verified by an independent test of the E-PERM calibration based on measurements with the NIST radon-in-water standard generator.

Effect of radiation rate on electret ionization chambers

The dependence of radiation-induced conductivity (RIC) on radiation rate in 254 mu m thick Teflon polyfluoroethylene propylene (FEP) film used in a electret ionization chamber (EIC) is discussed and measured with regard to radiation dosimetry. Ideally, air-kerma, a quantity linearly related to dose, can be determined through measurement of the surface-charge density on the electret surface before and after irradiation and observing the difference. However, RIC permits trapped surface charge to migrate through the polymer and recombine at the collecting electrode which results in a reduced EIC charging efficiency and an overestimation of air-kerma in radiation dosimetry. The response of the EIC to a given air-kerma is recorded as a function of air-kerma rate. It is predicted and observed that surface-charge loss does depend on air-kerma rate. With proper adjustment of physical parameters however, a suitably wide range of air-kerma rates can be found over which response is flat.

Electret method for continuous measurement of the concentration of radon in water.

A passive system using an electret ion chamber to measure dissolved radon in a water sample has been recently described. In the current work, an electret ion chamber has been used to measure time-averaged concentration of dissolved radon in water. A steady concentration of radon in water is generated by bubbling radon gas into water in a 20-L jar and maintaining constant rates of feed and bleed of the water. To perform the measurement, the outgoing water flows into a 4-L cylindrical chamber. Air is bubbled at 1 L min-1 through a 10 cm long sintered stainless steel tube immersed in this water releasing the radon from water into the chamber volume. A 1-L electret ion chamber ("H" chamber) loaded with an electret is hung in the 4-L chamber. Radon diffuses into the "H" chamber through its tyvek (carbon-coated) covered openings. The radon concentration in air is measured from the change in electret voltage. The concentration of radon in water is then obtained from the concentration of radon in air and the air and water flow rates. For comparison, the radon concentration in water was measured using a standard liquid scintillation counting method. For the concentration range covered (4.7 to 72 Bq L-1), there was a good agreement between the two methods.

Monitoring of 222Rn in Taiwanese Hot Spring SPA Waters Using a Modified Electret Ion Chamber Method

222Rn concentrations in some Taiwanese hot spring spa waters have been monitored using commercially available electret ion chambers (EIC). The use of two EIC units for measuring radon concentrations in the air phase and voltage dependent correction factors for subtracting gamma contributions resulted in improved accuracy.

Improved modeling of surface charge distributions in electret ionization chambers

Additional considerations are discussed concerning the modeling of time-dependent surface charge distributions in electret ionization chambers during the charging and discharging of electrets with ionizing radiation. Estimates of position-dependent ion density in the charging chamber are made using (a) a single-scattering calculation of ionization due to recoil electrons and (b) an isotropic, inverse-square approximation of ionization density. These estimates are used in conjunction with a subroutine which solves Laplace’s equation for electric field and tracks charge carrier trajectories from the point of origin in the chamber to an electret surface where the charge becomes trapped. The results of improved measurements are also shown and compared with calculations.

Radiation-induced conductivity of Teflon in electret ionization chambers

Studies of radiation-induced conductivity (RIC) of 254 mu m thick Teflon polyfluoroethylene propylene (FEP) film used in an electret ionization chamber (EIC) for charging and discharging of the electret are discussed. The EIC can be used to measure air-kerma from the amount of electret surface charge that has been neutralized by ions created in the chamber's sensitive volume. RIC permits the trapped surface charge to migrate through the polymer and recombine at the collecting electrode, which results in a reduced EC charging efficiency and an overestimation of air-kerma. A semi-empirical equation was developed to calculate time-dependent RIC as a function of air-kerma rate and electric field in the Teflon (FEP) film for steady-state and non-steady-state conditions. It was found that the air-kerma rate (dose rate) exponent is constant while the electric-field exponent is time dependent. It is found that RIC in Teflon (FEP) of this thickness causes air-kerma as measured with EICS to be very air-kerma rate dependent at low air-kerma rates. A discussion on the limitation of EICS due to this problem is given.

Evaluation of Electret Ion Chamber for Tritium Measurement

Commercial E-PERM radon-in-air monitors modified to detect tritium in air have been evaluated. Each monitor consists of a small ion chamber with access holes around the sides to allow the air to diffuse into the chamber, and an electret at the bottom to establish an electrostatic potential. Radioactive gas inside the volume generates ions, which are collected by the electret. The reduction of charge (and subsequent reduction in surface potential) on the electret is a measure of the integrated exposure. Two types of detectors, a 50 cm3 model and a 200 cm3 model, were tested for tritium-in-air concentrations from 1 to 60 MBq m-3, and gamma-absorbed dose rates from background levels to 50 microGy h-1. The HTO-in-air response of the modified E-PERM monitors was 3.3 +/- 0.3 V MBq-1 m3 h-1 for the 200 cm3 and 0.8 +/- 0.2 V MBq-1 m3 h-1 for the 50 cm3 monitor. For external gamma radiation (226Ra), the 200 cm3 chamber gave a response of 7.6 +/- 1.8 V microGy-1 and the 20 cm3 chamber 1.8 +/- 0.5 V microGy-1. The detection limit was about 3.6 and 15.2 MBq m-3 h for the 200 and 50 cm3 chambers, respectively. The accuracy and limit of detection of the electret detectors are limited by the accuracy in measuring the surface potential on the electret.

Modeling of surface charge distributions in electret ionization chambers

Computer modeling of the change of electret surface-charge distribution within electret ionization chambers (EIC) during the electret charging and discharging processes are described. Assuming a uniform and constant rate of ion generation, the theory of ion recombination in air is applied to Laplace’s equation to develop a description of the rate of charge accumulation and surface charge distribution. It is shown that distortions of electric fields within the air gap of the EIC control the distribution of charge accumulation, while saturation conditions, that determine the level of recombination of charges within the air gap of the EIC, control the maximum potential that can be deposited onto the electret surface. Results of modeling are compared with measured data, and suggestions for refinement in the model are discussed.

Recent Advances in Electret Ion Chamber Technology for Radiation Measurements

Recent Advances in Electret Ion Chamber Technology for Radiation Measurements

Recent Advances in Electret Ion Chamber Technology for Radiation Measurements

Recent Advances in Electret Ion Chamber Technology for Radiation Measurements

Electret Ion Chamber Radon Monitors Measure Dissolved 222Rn in Water

This paper describes a simple and relatively inexpensive method of determining the concentration of dissolved 222Rn in water. The method involves a recently developed electret-passive environmental radon monitor, which uses an electret ion chamber. The procedure consists of sealing a known volume of a carefully collected water sample with one of these monitors in an exposure container and determining the average equilibrium 222Rn gas concentration in the air phase during the exposure time period. This average concentration can then be used to calculate the 222Rn concentration in the original water sample. Identical samples were analyzed both by this new method and by a standard liquid scintillation method, and the results were compared over a wide range of 222Rn concentrations. There was good agreement except that the electret ion chamber method gave results that were consistently lower by about 15%. This bias in the results was attributed to both 222Rn losses during sample handling and possibly to some errors in the assumptions made in the theoretical model. A correction factor is recommended to bring the results of this technique into agreement with the standard method. The procedures are simple and economical and can be easily employed by many primary 222Rn-measuring laboratories currently using these monitors for measuring indoor 222Rn.

Characteristics of a radiation-charged electret dosimeter

The radiation-charged electret ionization chamber uses an electret formed in situ by applying a bias voltage to the chamber electrodes while the chamber is being irradiated with X-rays. An electrometer permits measurement of the charge on the electret surface before and after the use of the chamber as a dosimeter. The authors present measurements of dosimeter range, sensitivity and energy dependence as functions of bias potential, electrode separation, guard ring size and various materials. Reproducibility permits detection as low as 80 mu Gy, with range to approximately 5 Gy, depending on the design of the chamber, with charge retention properties similar to electrets formed isothermally from corona discharge.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electret Ion Chamber System for Measurement of Environmental Radon and Environmental Gamma Radiation

Electret Ion Chamber System for Measurement of Environmental Radon and Environmental Gamma Radiation

Electret Ion Chamber System for Measurement of Environmental Radon and Environmental Gamma Radiation

Electret Ion Chamber System for Measurement of Environmental Radon and Environmental Gamma Radiation

Methods of measuring ambient atmospheric radon and radon surface flux associated with phosphogypsum treatment of a Florida spodosol soil

Abstract Phosphogypsum (PG) is a by‐product gypsum (CaSO4.2H2O) of the manufacture of phosphoric acid and is a major potential source of S and Ca for crops. The PG used in this study contained 25.6% Ca, 62.1% SO4‐S, and 18 pCi 226Ra g‐1 . Radon (222Rn) emanations from a bahiagrass (Paspalum notatum Flugge) pasture on a typical Florida Spodosol fertilized with PG up to 4.0 Mg ha−1 as a source of S were measured as atmospheric ambient radon (pCi L−1) using electret ion chambers (EIC) and as radon surface flux (pCi m2 s−1) using large‐area activated charcoal canisters (LAACC). Atmospheric ambient radon values before PG application measured twice, each over a 30‐d period from June 11 to August 24, 1990, and after PG application measured seven times, each over a 30‐ or 60‐d period from August 25, 1990 to July 16, 1991, averaged 0.17±0.07 and 0.19±0.09 pCi L−1, respectively. Post‐application measurements over treated and untreated plots (including external controls) were 0.20±0.08 and 0.18±0.09 pCi L−1, respect...

Surface charge distribution during the charging and discharging of electrets produced in electret ionization chambers

Spatial charge distributions during the charging and discharging processes of thin film polymer electrets produced by ionizing radiation in air are presented. The charge distributions were measured for various externally applied potentials and air gap thicknesses of electret ionization chambers (EICs). The results show important limitations in charging electrets with this technique in EIUs of relatively large air gaps, but show excellent results with EICs of small air gaps. Practical problems of achieving maximum charge densities corresponding to the externally applied potential are discussed. The change in charge distributions during the charging and discharging stages with various external potentials and air gaps is also presented and analyzed, and possible causes for the patterns are given. Measurements of charge distributions during discharge describe the neutralization process involved in EICs and suggest limitations to the practical size of chambers. >

Elevation Correction Factors For E-Perm Radon Monitors

E-PERM radon monitors are based on the principle of electret ion chambers and are usually calibrated in a standard radon chamber located at sea level. Corrections are needed if the monitors are used at elevations other than sea level. These were experimentally determined for three models of commercially available electret ion chambers (E-PERM) as functions of elevation above sea level. These corrections are minor and should be applied for obtaining more accurate results.

The determination of dissolved radon in water supplies by the E-PERM system (electret ionization chamber)

Elevated levels of radon may be found in well waters and individuals who ingest such waters may receive significant radiation doses. This paper discusses the experience of the Radiation Protection Service in using the E-PERM system for measuring dissolved radon in water samples.

Electret ion chamber for radon monitoring : Robert W Ramsey, Payasad Kotrappa assigned to Rad Elec Inc

Electret ion chamber for radon monitoring : Robert W Ramsey, Payasad Kotrappa assigned to Rad Elec Inc