High-pressure Ionization Chamber Research Articles

Environmental Gamma Dose Rate Monitoring and Radon Correlations: Evidence and Potential Applications

Gamma emitting radionuclides naturally present in the Earth’s crust and the radon exhaled by soil in the atmosphere with its short-lived progeny are two of the main contributors to the environmental gamma dose rate that typically characterizes an outdoor measurement site. The present work aims to investigate variations in the environmental dose-rate time series originated by different natural phenomena, such as weather and seismic events, which can modify the radon concentration in the air. The data analyzed here were acquired over a five-year period using a Reuter–Stokes high-pressure ionization chamber placed in the ENEA Casaccia Research Center (Rome, Italy), from November 2013 to December 2018. The detector was set to take a single measurement of the equivalent ambient dose H*(10) every 15 min, thereby collecting more than 184,000 values over the five-year period under consideration. The detector’s sensitivity to the short-lived radon progeny was verified in a preparatory study performed by means of simultaneous radon flux measurement on field. Variations induced by meteorological events as well as variations potentially induced by seismic events were investigated by implementing different data analysis techniques. In the latter case, a retrospective preliminary study was conducted, applying the ARFIMA class of models in order to test the method’s potential. The analysis techniques, results and potential applications are presented and discussed in this article.

Quality control measures of thermoluminescent dosimetry system used in environmental radiation monitoring

Objective To discuss the quality control measures of the thermoluminescent dosimetry system and to verify its propriety of when used in environmental radiation monitoring. Methods The quality control measures included the stability test, the dispersibility screening and the uncertainty evaluation of measurement results of the TLD reader and TLD detector, in addition, the environmental radiation accumulated dose monitoring results obtained by the high pressure ionization chamber were compared with those by the thermoluminescent dosimetry system. Results The variation range of TLD reader’s light source coefficient is within 0.070~0.073 during the preheating and measuring process, which meets the requirements of stability; The χ 2 value of the TLD detector is 2.088, which obeys the normal distribution; The thermoluminescent dosimetry system’s nonlinear response, coefficient of variation and energy response meet the measurement requirements; There is a deviation of −6.58% the largest between the cumulative dose obtained by TLD and the high pressure ionization chamber. Conclusion The quality control measures discussed in this paper can be used as a reference for similar thermoluminescent dosimetry system. Our system has passed all the tests and can meet the environmental radiation cumulative dose monitoring requirements. 摘要： 目的 探讨热释光测量系统的质量控制方法, 验证热释光测量系统能否准确有效的用于环境辐射水平监测。 方法 采取的环境辐射监测用热释光测量系统质量控制方法包括热释光测量系统的稳定性检验、热释光探测器的分 散性筛选、测量结果不确定度评定, 并与高气压电离室测量方法进行对比。 结果 读出器预热及测读过程中光源系数 变化范围在 0.070~0.073, 稳定性符合使用要求; 热释光探测器的 χ 2 值为 2.088, 服从正态分布;热释光测量系统满足 非线性响应、变异系数和能量响应的计量要求; 热释光累积剂量测量结果与高气压电离室相比偏差最大 −6.58%。 结论 本实验室采取的质控措施可作为同类热释光测量系统的质控措施的参考;本实验室的热释光测量系统通过了 各项检验, 满足环境辐射累积剂量监测的使用要求。

A FEASIBILITY TEST FOR QUICK RADON RISK ASSESSMENT BY MEASURING AN IN SITU RADIATION DOSE RATE.

Radon concentration was estimated using an accumulation chamber equipped with AlphaGUARD radon monitor. It varies from 12.6±1.20 to 363±19.3Bqm-3 with a mean value of 180±11.2Bqm-3. A good correlation between radium content and radon concentrations was obtained of R=0.754, which suggests that radium is the main reason of releasing radon to the atmosphere. Radon emanation coefficient and exhalation rate were also calculated. Furthermore, the radiation dose rate was measured with a high-pressure ionization chamber detector. The radiation dose rate was strongly correlated with the radon concentration and exhalation rate of R=0.85 and 0.63. The obtained results support our idea that the radiation dose rate can be a good indicator to the radon level in the atmosphere. In addition, the dependence of radon concentration on the water content was discussed.

PROCEDURES TO MEASURE MEAN AMBIENT DOSE EQUIVALENT RATES USING ELECTRET ION CHAMBERS.

The capabilities of electret ion chambers (EICs) to measure mean ambient dose equivalent rates were investigated by performing both laboratory and field studies of their properties. First, EICs were ‘calibrated’ to measure ambient gamma dose equivalent in the Ionizing Calibration Laboratory of the Greek Atomic Energy Commission. The EICs were irradiated with different gamma photon energies and from different angles. Calibration factors were deduced (electret’s voltage drop due to irradiation in terms of ambient dose equivalent). In the field studies, EICs were installed at eight locations belonging to the Greek Early Warning System Network (which is based on Reuter-Stokes ionization chambers) for three periods, averaging 5 months each. In the same locations, in situ gamma spectrometry measurements were performed with portable germanium detectors. Gamma ambient dose equivalent rates were deduced by the in situ gamma spectrometry measurements and by soil sample analysis. The mean daily electret potential drop (in Volts) was compared with the mean daily ambient dose equivalent, measured with a portable HPGe detector and Reuter-Stokes high-pressure ionization chambers. From these measurements, ‘field’ calibration factors (electret’s voltage drop due to gamma radiation in terms of ambient dose equivalent) were deduced and found in very good agreement with the values deduced in Laboratory. The influence of cosmic radiation and the intrinsic voltage loss when performing long-term environmental gamma measurements with EICs, was estimated.

Development of a silicon microstrip detector prototype for ultra-fast imaging at a synchrotron radiation beam

A method of imaging of ultra-fast processes, like explosion or fast combustion, at a synchrotron radiation beam is being developed at the Siberian Synchrotron and Teraherz Radiation Center (SSTRC) . Two stations are operating at beam line 0 at the VEPP-3 storage ring and at beam line 8 at the VEPP-4M storage ring. Both stations are equipped with the detector for imaging of explosions DIMEX, based on high pressure ionization chamber, and allowing to record up to 100 one dimensional images with the frame rate of 8 MHz. However the maximum flux that DIMEX can detect is limited as well as spatial resolution and frame rate because of gas technology used. In view of significant increase of SR flux at the VEPP-4M beam line due to the new 9-pole 2 T wiggler, a new detector is being developed for this beam line, based on Si microstrip sensor. The first Si microstrip detector prototype has been mounted with new specially developed front-end ASIC that allows to record data with the rate of 50 MFrames/s. The first measurements with this prototype demonstrated significant improvement of all critical parameters of the detector compared to the gaseous version.

Monte Carlo Simulation of Angular Response Function of Airborne Gamma Spectrometer

The angular response function F(θ, φ) is used as an airborne gamma spectrometer to measure the basic physical quantity of the contribution of each nuclide to the total dose rate by the all-energy peak method, which is facing the difficulty of experimental calibration. In this paper, the Monte Carlo program MCNP5 is used to calculate the full-energy peak angle response function F(θ, φ) of a single NaI(Tl) crystal (40 cm × 10 cm × 5 cm) to Cs-137. It has been verified that when the point source is directly below the spectrometer, the relative error between the dose rate calculated by a single crystal γ spectrometer using the all-energy peak method and the dose rate measured by the high-pressure ionization chamber does not exceed 15%. When the distance between the crystal and the point source is 7 m and the elevation and azimuth angles are both 45°, the relative error between the two is 13.891%, which verifies the feasibility of the analog scale of the angular response function.

Operation of a silicon microstrip detector prototype for ultra-fast imaging at a synchrotron radiation beam

A method of imaging of ultra-fast processes, like explosions or fast combustion, at a synchrotron radiation beam is being developed at the Siberian Synchrotron and Terahertz Radiation Center (SSTRC). Two stations are equipped with the detector for imaging of explosions, DIMEX, based on high pressure ionization chamber, and allowing to record up to 100 one dimensional images with a frame rate of 8 MHz. However the maximum flux that DIMEX can detect is limited as well as the spatial resolution and the frame rate because of the gas technology used. In view of the significant increase of SR flux at the VEPP-4M beam line due to the new 9-pole 2 T wiggler, a new detector is being developed for this beam line, based on Si microstrip sensor. The first Si microstrip detector prototype has been mounted with a new specially developed front-end ASIC that allows to record data with a rate up to 40 MFrames/s. The first measurements with this prototype demonstrated significant improvement of all critical parameters of the detector compared to the gaseous version. The maximum detected photon rate before saturation is increased to 20000 photons/(channel x bunch) compared to 1500 photons/(channel x bunch). The spatial resolution is improved from 240μm to 130μm (FWHM) and the frame rate is increased by a factor 5.

Standardisation of Rhenium-188 and determination of calibration factors for secondary standard and radionuclide calibrator

The use of Rhenium-188 for various therapeutic applications in the field of nuclear medicine has increased in recent years due to its favourable properties like decay scheme, cost effective availability and easy chemistry. Two independent measuring setups were used to standardise 188Re radioactive solution. The modus operandi of standardisation was 4πβ-γ coincidence technique where the beta detection was done by proportional counting and liquid scintillation counting and the gamma detection was done by using NaI(Tl) detectors. The secondary standard, high pressure ionisation chamber type Centronic IG12, 20A was calibrated with the standardised 188Re solution and the sensitivity coefficient (pA MBq−1) was determined. To enhance the accuracy of the commercial radionuclide calibrator and to ensure that patients receive optimum dose of these radiopharmaceuticals, calibration number of the Capintec CRC-15β radionuclide calibrator was also verified. This paper presents the standardisation of 188Re radioactive solution by primary methods and calibration of BARC secondary standard ionisation chamber system and a Capintec CRC-15β radionuclide calibrator.

Uncertainties and characteristic limits of counting and spectrometric dosimetry systems

In the event of a radiological emergency, early and reliable knowledge of radioactivity concentrations is important information for organising countermeasures to protect the general public and emergency workers. This is ensured by all European countries in operating airborne radioactivity and dose rate early warning networks. To increase the provided information, the development of new secondary standards based on scintillation detectors for the measurement of ambient dose rate equivalent was initiated in 2014. This paper shows the state-of-the-art of uncertainties and characteristic limits of low dose rate measurement that can be achieved by scintillation-based detector (CeBr3) and gas-based detectors (a high-pressure ionization chamber, HPIC). The comparison of the devices shows the performance and the metrological potential of the CeBr3 detector: Its uncertainty is already very close to the uncertainty of reference values. Looking at the question how to select a reference instrument, the CeBr3 detector with a special data evaluation is even superior to the HPIC and qualifies therefore as a modern secondary standard: Providing both, dose rate and nuclide information.

Upgrading a Detector for Studying Fast Processes on a Beam of Synchrotron Radiation

The current stage of the upgrade of the DIMEX detector for studying fast processes on a synchrotron radiation (SR) beam is described. The current version of the DIMEX is a one-dimensional high-pressure ionization chamber with a fast electron component readout. The detector can record photon fluxes from each bunch separately without mixing photons from different bunches. The maximum flux the DIMEX can detect is limited by the space charge of positive ions in a high-pressure gas. To substantially improve this and other parameters of the detector, it was decided to switch to microstrip silicon technology. A prototype based on a silicon-microstrip sensor was developed along with a special integrated circuit (ASIC) for reading out the signals from this prototype. The first tests of the new DIMEX-Si prototype on an SR beam show that it is superior to the gaseous version in all respects. Results are presented from the first tests of the silicon-microstrip detector prototype on the SR beam of the VEPP-4M storage ring.

Application of a SrI2(Eu) scintillation detector to in situ gamma-ray spectrometry in the environment

Using scintillation detectors to spectrometrically determine dose rate is useful in response to a nuclear accident, because the nuclide contribution in the measured dose rate can be determined. However, to select an appropriate scintillator for in situ gamma-ray spectrometry in the environment, energy resolution and counting efficiency should be evaluated. A SrI2(Eu) crystal is one of the promising scintillators, with good energy resolution and light output performance. But its long scintillation decay time of about 1 μs needs to be well matched with the signal processing unit of the gamma-ray spectrometer to avoid degrading its good performance. In this study a performance test was first conducted to determine the optimized pulse shaping time in the gamma-ray detection process. In addition, a Monte Carlo simulation of the SrI2(Eu) detector was performed to establish the algorithm for the spectrometric determination of dose rate. Finally, in situ gamma-ray spectrometry was performed with the SrI2(Eu) detector to determine the ambient dose rate, as well as the dose rate of nuclides in the environment. The results were successfully compared with those of HPIC (high pressure ion chamber), portable HPGe (high purity Ge), and NaI(Tl) detectors at the same site.

Comparative study of precise measurements of natural radionuclides and radiation dose using in-situ and laboratory \u03b3-ray spectroscopy techniques

In this study, in-situ and laboratory γ-ray spectroscopy techniques were compared to evaluate the activity concentration of natural radionuclides in soil. The activity concentrations of 238U (226Ra), 232Th, and 40K in the soil in 11 sites were simultaneously measured with in-situ portable HPGe and the NaI(Tl) detectors. In parallel, 55 soil samples collected from these sites were analyzed with a laboratory γ-ray spectroscopy technique (HPGe). A strong correlation was observed between the in-situ and laboratory HPGe techniques with a linear correlation coefficient (R2) of 0.99 for 226Ra and 232Th and 0.975 for 40K, respectively. The in-situ HPGe technique shows a strong correlation with the NaI(Tl) detector. γ-Rays cps of 226Ra, 232Th, and 40K of the NaI (Tl) detector were then converted to specific activities (Bq kg−1 unit) in soil using the empirical formulas obtained in this study. The absorbed dose rate in air at 1 m height above ground due to these radionuclides was calculated using the Beck’s formula and the results were compared with measured values obtained with an high pressure ionization chamber. The results of the calculated and measured dose rate show a strong correlation of R2 = 0.96. The reliability and precision of analytical spectroscopy techniques of radioactivity and radiation dose were confirmed in this work.

Evaluation of background radiation dose contributions in the United Arab Emirates

The natural background radiation consists of three main components; cosmic, terrestrial, and skyshine. Although there are currently methods available to measure the total dose rate from background radiation, no established methods exist that allow for the measurement of each component the background radiation. This analysis consists of a unique methodology in which the dose rate contribution from each component of the natural background radiation is measured and calculated. This project evaluates the natural background dose rate in the Abu Dhabi City region from all three of these components using the developed methodology. Evaluating and understanding the different components of background radiation provides a baseline allowing for the detection, and possibly attribution, of elevated radiation levels. Measurements using a high-pressure ion chamber with different shielding configurations and two offshore measurements provided dose rate information that were attributed to the different components of the background radiation. Additional spectral information was obtained using an HPGe detector to verify and quantify the presence of terrestrial radionuclides. By evaluating the dose rates of the different shielding configurations the comic, terrestrial, and skyshine contribution in the Abu Dhabi City region were determined to be 33.0 ± 1.7, 15.7 ± 2.5, and 2.4 ± 2.1 nSv/h, respectively.

RESPONSE OF THE GREEK EARLY WARNING SYSTEM REUTER-STOKES IONIZATION CHAMBERS TO TERRESTRIAL AND COSMIC RADIATION EVALUATED IN COMPARISON WITH SPECTROSCOPIC DATA AND TIME SERIES ANALYSIS

The Telemetric Early Warning System Network of the Greek Atomic Energy Commission consists mainly of a network of 24 Reuter-Stokes high-pressure ionization chambers (HPIC) for gamma dose rate measurements and covers all Greece. In the present work, the response of the Reuter-Stokes HPIC to terrestrial and cosmic radiation was evaluated in comparison with spectroscopic data obtained by in situ gamma spectrometry measurements with portable hyper pure Germanium detectors (HPGe), near the Reuter-Stokes detectors and time series analysis. For the HPIC detectors, a conversion factor for the measured absorbed dose rate in air (in nGy h-1) to the total ambient dose equivalent rate Ḣ*(10), due to terrestrial and cosmic component, was deduced by the field measurements. Time series analysis of the mean monthly dose rate (measured by the Reuter-Stokes detector in Thessaloniki, northern Greece, from 2001 to 2016) was performed with advanced statistical methods (Fast Fourier Analysis and Zhao Atlas Marks Transform). Fourier analysis reveals several periodicities (periodogram). The periodogram of the absorbed dose rate in air values was compared with the periodogram of the values measured for the same period (2001-16) and in the same location with a NaI (Tl) detector which in principle is not sensitive to cosmic radiation. The obtained results are presented and discussed.

Normalization of energy-dependent gamma survey data.

Instruments and methods for normalization of energy-dependent gamma radiation survey data to a less energy-dependent basis of measurement are evaluated based on relevant field data collected at 15 different sites across the western United States along with a site in Mongolia. Normalization performance is assessed relative to measurements with a high-pressure ionization chamber (HPIC) due to its "flat" energy response and accurate measurement of the true exposure rate from both cosmic and terrestrial radiation. While analytically ideal for normalization applications, cost and practicality disadvantages have increased demand for alternatives to the HPIC. Regression analysis on paired measurements between energy-dependent sodium iodide (NaI) scintillation detectors (5-cm by 5-cm crystal dimensions) and the HPIC revealed highly consistent relationships among sites not previously impacted by radiological contamination (natural sites). A resulting generalized data normalization factor based on the average sensitivity of NaI detectors to naturally occurring terrestrial radiation (0.56 nGy hHPIC per nGy hNaI), combined with the calculated site-specific estimate of cosmic radiation, produced reasonably accurate predictions of HPIC readings at natural sites. Normalization against two to potential alternative instruments (a tissue-equivalent plastic scintillator and energy-compensated NaI detector) did not perform better than the sensitivity adjustment approach at natural sites. Each approach produced unreliable estimates of HPIC readings at radiologically impacted sites, though normalization against the plastic scintillator or energy-compensated NaI detector can address incompatibilities between different energy-dependent instruments with respect to estimation of soil radionuclide levels. The appropriate data normalization method depends on the nature of the site, expected duration of the project, survey objectives, and considerations of cost and practicality.

Design and verification of the shielding around the new Neutron Standards Laboratory (LPN) at CIEMAT

The construction of the new Neutron Standards Laboratory at CIEMAT (Laboratorio de Patrones Neutrónicos) has been finalised and is ready to provide service. The facility is an ∼8 m×8 m×8 m irradiation vault, following the International Organization for Standardization 8529 recommendations. It relies on several neutron sources: a 5-GBq (5.8× 10(8) s(-1)) (252)Cf source and two (241)Am-Be neutron sources (185 and 11.1 GBq). The irradiation point is located 4 m over the ground level and in the geometrical centre of the room. Each neutron source can be moved remotely from its storage position inside a water pool to the irradiation point. Prior to this, an important task to design the neutron shielding and to choose the most appropriate materials has been developed by the Radiological Security Unit and the Ionizing Radiations Metrology Laboratory. MCNPX was chosen to simulate the irradiation facility. With this information the walls were built with a thickness of 125 cm. Special attention was put on the weak points (main door, air conditioning system, etc.) so that the ambient dose outside the facility was below the regulatory limits. Finally, the Radiation Protection Unit carried out a set of measurements in specific points around the installation with an LB6411 neutron monitor and a Reuter-Stokes high-pressure ion chamber to verify experimentally the results of the simulation.

A real-time multichannel detector system for large-scale environmental radiation survey

In this work, we established a real-time multichannel detector system for large-scale environmental radiation survey. The system consists of a Berkeley Lab cosmic-ray detector for the measurement of muons, a moderated He detector for neutrons, a NaI(Tl) as well as a HPGe spectrometer for terrestrial gamma rays, and a high pressure ionization chamber, which responses to both cosmic rays and terrestrial gamma rays. The measured data of these five detector channels as well as signals from a global position system are acquired and displayed by a LabVIEW program on a notebook computer every one minute (10 min for HPGe and 20 min for NaI(Tl) gamma-ray spectrometers). The advantage and merit of this multichannel detector system have been demonstrated by test runs with the equipment set up both on a train and on a bus to show in real time the variation of cosmic-ray intensity as a function of altitude and the gamma-ray dose rates as well as the relative concentrations of the natural radioactive elements over a large survey area. This real-time multichannel detector system was originally developed for natural background radiation measurements for popular science education to general public, however, due to the specific features of each detector of the system it appears to be an ideal system for radiation survey over a large radiation polluted or contaminated area resulted from a severe nuclear accident, such as Fukushima Dai-Ichi Nuclear Power Plant accident.

Gamma dose rate due to natural and manmade radiation sources from a nuclear facility in Mexico

The environmental external gamma dose rate has been determined at the Mexican Nuclear Research Centre and surrounding communities, located in a forest area. Outdoor direct measurements of external gamma exposure and absorbed dose rates in air were performed using passive integrating thermoluminescent dosimeters. Radiological measurements were also carried out with a portable high pressure ionization chamber. The gamma dose rate was evaluated from data obtained along 10 years measurements. The activity concentrations of 40K, 226Ra, 232Th, 137Cs, and 235U in surface soil samples at sampling sites are also presented. The radionuclide activity concentrations were determined by low background gamma spectrometry with hyper-pure germanium detectors. A site specific lineal model to describe the relationship between the external gamma dose rate and the 226Ra concentration values in the soil is proposed.

Monte Carlo Modeling of Ion Chamber Performance Using MCNP

Ion Chambers have a generally flat energy response with some deviations at very low (<100 keV) and very high (>2 MeV) energies. Some improvements in the low energy response can be achieved through use of high atomic number gases, such as argon and xenon, and higher chamber pressures. This work looks at the energy response of high pressure xenon-filled ion chambers using the MCNP Monte Carlo package to develop geometric models of a commercially available high pressure ion chamber (HPIC). The use of the F6 tally as an estimator of the energy deposited in a region of interest per unit mass, and the underlying assumptions associated with its use are described. The effect of gas composition, chamber gas pressure, chamber wall thickness, and chamber holder wall thicknesses on energy response are investigated and reported. The predicted energy response curve for the HPIC was found to be similar to that reported by other investigators. These investigations indicate that improvements to flatten the overall energy response of the HPIC down to 70 keV could be achieved through use of 3 mm-thick stainless steel walls for the ion chamber.

Comparative Measurements of the External Radiation Exposure in a 137Cs Contaminated Village in Belarus Based on Optically Stimulated Luminescence in NaCl and Thermoluminescence in LiF

Laboratory studies have shown that ordinary household salt (NaCl) exhibits several promising properties for retrospective dosimetry; e.g., a linear dose response and a low detection limit, down to a few mGy or even less. In an attempt to test NaCl as a dosimeter outside the laboratory, the first results from the use of NaCl as a dosimeter under normal environmental conditions are reported here. For this purpose, special dosimeter kits with NaCl and lithium fluoride (LiF) chips were designed. The dosimeter kits were positioned at different locations in a Chernobyl Cs-contaminated village in Belarus during the summers of 2008, 2009, and 2010. The results from the two luminescent detectors were also compared with those of measurements carried out with a handheld 75 cm NaI(Tl) detector and with a 8 dm high pressure ionization chamber. The radiation level in the village was inhomogeneous, and depending on the type of house and countermeasures carried out, the ambient dose rate inside and around the houses varied between 0.05 μSv h and 0.50 μSv h. Based on the different measurements, the annual external effective dose to a hypothetical adult population in the village was estimated as 1-1.5 mSv y. Detector readings from the two luminescent materials correlated relatively strongly to that of the ambient survey NaI(Tl) detector. After three repeated surveys using similar dosimeter kits for prospective dosimetry, the potential use of ordinary household salt as a complement to other techniques for retrospective dose estimations is more evident, and shortcomings of the technique have been identified.