Gas Proportional Counter Research Articles

A Simple Method to Screen for Radiostrontium in Water by Ion Exchange Chromatography.

Radiostrontium isotopes (Sr, Sr, and Sr) are major fission by-products in nuclear reactors, in radiological events, and in environmental radioactive contamination. A method to analyze Sr and Sr in water has been developed using gradient elution with dilute hydrochloric acid and cation exchange resin, followed by carbonate precipitation. Counting was done on a gas proportional counter. The sample was recounted a second time after 2 to 3 wk to permit Y, a progeny of Sr, to achieve secular equilibrium and to allow Sr and Sr to be determined. This method was found to be simple, exhibiting high recovery, reduced use of hazardous chemicals, and lower cost compared to other current methods. An extensive comparison of the performance of the cation exchange method vs. a method using strong nitric acid (US Environmental Protection Agency Method 905.0) and a method using a specific strontium resin was conducted on performance test samples containing Sr (in a number of matrices) from the US Department of Energy's Mixed Analyte Performance Evaluation Program and mixed Sr- and Sr-containing water samples from the Environmental Resource Associates quality assurance program. The method described here is shown to yield comparable results to others.

Characterization of an array of gas-flow proportional counters for determination of gross alpha and gross beta in drinking water

The performance of an array of gas proportional counters (Model LB4200TM) was characterized for assessing gross radioactivity in drinking water. Among others, the examined parameters included detection efficiency and minimal detectable activity concentration. The study of the system parameters was conducted using water samples with known activities of 230Th and 90Sr and known salinity levels that were prepared according to the co-precipitation and evaporation methods. The detection efficiencies for alpha and beta in water samples were found to be 16% and 37%, respectively. In addition, the extraction efficiencies of radionuclides in water samples using the co-precipitation and evaporation methods were found to be approximately 90%. Minimal detectable concentrations for gross alpha and gross beta were found to be typically 0.02 Bq/L and 0.13 Bq/L, respectively. Results demonstrate that although the system detectors as well as the prepared water samples have relatively small diameters (40–49 mm), the system and methods used meet the criteria for determining gross alpha and gross beta in drinking water.

Development of a multi-segmented proportional gas counter for β-decay spectroscopy at KISS

We developed a multi-segmented proportional gas counter to perform β-decay spectroscopy of neutron-rich nuclei extracted from KEK Isotope Separation System (KISS). The 32 segmented gas counters allow us two-dimensional tracking of the events to identify β-ray events by discriminating background events. The detectors being by low-density material of thin aluminized Mylar foils and P10 gas enabled us to detect low energy electrons down to 100 keV. The absolute detection efficiency was 45% at Qβ=1 MeV, and the measured background event rate was 0.11 cps. The detector was applied to perform β-decay spectroscopy and hyperfine structure measurements of neutron-rich isotopes of Pt, Ir, and Os. We started to develop the gas counter with three-dimensional tracking by replacing the material of anode wire from BeCu to resistive thin carbon to reduce the background event rate below 0.01 cps.

Promising Neutron Detector with Anticoincidence Protection

The method of remote neutron and gamma spectrometry of bodies in the solar system (the Moon, Mars, and Mercury) has been used for several decades to estimate the nuclear composition of these objects and the hydrogen abundance in their subsurface layers. Proportional gas counters based on helium-3 (3He), which have the maximum efficiency of detecting thermal and epithermal neutrons, are used most often for measuring the low-energy neutron component. However, the data from LEND and FREND space experiments with large-volume and high-pressure helium counters revealed the noise contamination of lower channels of the neutron component due to the sensitivity of such counters to cosmic charged particles. The model of a promising neutron detector with anticoincidence protection, which is free from this drawback, is presented below.

Measurement of the gamma-ray emission probability of 131mXe

131mXe has been standardized by means of an internal gas proportional counting system, employing a length-compensated method. The activity concentration of 131mXe was measured with a relative standard uncertainty of 0.6%. The gamma-ray emission probability of 131mXe was then determined as 0.0196(4) by measuring a standard sample of 131mXe using a high-purity germanium (HPGe) spectrometer.

Electroluminescence TPCs at the thermal diffusion limit

The NEXT experiment aims at searching for the hypothetical neutrinoless double-beta decay from the 136Xe isotope using a high-purity xenon TPC. Efficient discrimination of the events through pattern recognition of the topology of primary ionisation tracks is a major requirement for the experiment. However, it is limited by the diffusion of electrons. It is known that the addition of a small fraction of a molecular gas to xenon reduces electron diffusion. On the other hand, the electroluminescence (EL) yield drops and the achievable energy resolution may be compromised. We have studied the effect of adding several molecular gases to xenon (CO2, CH4 and CF4) on the EL yield and energy resolution obtained in a small prototype of driftless gas proportional scintillation counter. We have compared our results on the scintillation characteristics (EL yield and energy resolution) with a microscopic simulation, obtaining the diffusion coefficients in those conditions as well. Accordingly, electron diffusion may be reduced from about 10 mm/ sqrt{mathrm{m}} for pure xenon down to 2.5 mm/ sqrt{mathrm{m}} using additive concentrations of about 0.05%, 0.2% and 0.02% for CO2, CH4 and CF4, respectively. Our results show that CF4 admixtures present the highest EL yield in those conditions, but very poor energy resolution as a result of huge fluctuations observed in the EL formation. CH4 presents the best energy resolution despite the EL yield being the lowest. The results obtained with xenon admixtures are extrapolated to the operational conditions of the NEXT-100 TPC. CO2 and CH4 show potential as molecular additives in a large xenon TPC. While CO2 has some operational constraints, making it difficult to be used in a large TPC, CH4 shows the best performance and stability as molecular additive to be used in the NEXT-100 TPC, with an extrapolated energy resolution of 0.4% at 2.45 MeV for concentrations below 0.4%, which is only slightly worse than the one obtained for pure xenon. We demonstrate the possibility to have an electroluminescence TPC operating very close to the thermal diffusion limit without jeopardizing the TPC performance, if CO2 or CH4 are chosen as additives.

International inter-comparison exercise on $${}^{153}\hbox {Sm}$$

Samarium-153 ( $${}^{153}\hbox {Sm}$$ ) is a short-lived radionuclide that decays to stable europium-153 via beta emission, with subsequent de-excitation via gamma emission and internal conversion. Historical measurements of $${}^{153}\hbox {Sm}$$ by gamma spectrometry and beta liquid scintillation counting have shown a low bias compared to beta proportional counting. In order to investigate this, four national laboratories jointly conducted an experimental inter-comparison exercise on a certified $${}^{153}\hbox {Sm}$$ sample, created from neutron activation of samarium-152. Radiometric measurements were conducted using gamma spectrometry, liquid scintillation counting, gas proportional counting, and passivated implanted planar silicon detectors and compared across the four institutions against the certified value. The results from this experiment are presented together with a number of conclusions which suggest that the current published cumulative fission yield for $${}^{153}\hbox {Sm}$$ , as used by many laboratories, is approximately 15% high and is the likely cause of the previously observed bias.

Results of In-Depth Analysis of Data Obtained in the Experimental Search for 2K(2ν)-Capture in 78Kr

A brief description of the results of joint analysis of data obtained in long-term measurements of krypton samples differing in 78Kr content is presented. Low-background high-pressure proportional gas counters were used as detectors. The comparative analysis of experimental data on single and double K-capture provided the first estimate of the probability of production of a double K-shell vacancy in the process of K-shell electron capture in 81Kr: $${{P}_{{KK}}} = \left[ {5.7 \pm 0.8\,\,({\text{stat}}{\text{.}}) \pm 0.4\,\,({\text{syst}}{\text{.}})} \right] \times {{10}^{{ - 5}}}$$ . A new result for the half-life of 78Kr with respect to the 2K(2ν)-mode was also obtained: $${{T}_{{1/2}}} = \left[ {1.9_{{ - 0.7}}^{{ + 1.3}}\,\,({\text{stat}}{\text{.}}) \pm 0.3\,\,({\text{syst}}{\text{.}})} \right] \times {{10}^{{22}}}$$ years (90% CL).

New Constraints on the Axion–Photon Coupling Constant for Solar Axions

Resonance excitation of the 83Kr first nuclear level (E = 9.4 keV) by solar axions formed via the Primakoff mechanism is sought. The γ- and X-ray photons and the conversion and Auger electrons arising from the excited-level relaxation are detected with a gas proportional counter of a low-background detector in the underground Baksan Neutrino Observatory. The following experimental constraint is obtained for the product of the axion–photon coupling constant and the axion mass:|gAγ × mA| ≤ 6.3 × 10 -17 In the framework of the hadronic-axion model, this corresponds to a new axion-mass constraint of mA ≤ 12.7 eV at 95% C.L.

Methods of Radiocarbon Determination in Wine and Bone Samples by Gas Proportional Counting Technique

ABSTRACTAlthough radiocarbon accelerator mass spectrometry (14C AMS) surpasses conventional radiometric methods in many aspects, they still represent an interesting alternative, especially for studies unconstrained by sample size. Here we showed that the gas proportional counting technique can be used for bone samples, processed only by a simple ABA method, and ethanol, distilled from wine samples. The feasibility of the described methods was verified by successful dating of 11 well-preserved vertebrate bones of modern to 21 kyr BP age excavated from different caves in Slovakia from which collagen was also extracted, as well as by determination of 14C concentration in two modern western Slovakia vintages, which matches well the atmospheric Δ14C level for the respective region and grape vegetation period. Various empiric factors affecting the yield of the thoroughly tested procedures used for processing of samples and their optimization parameters are discussed as well.

Precise half-life measurement of the superallowed emitter S30

We have measured the half-life of 30S, the parent of a superallowed 0+-to-0+ beta transition, to high precision using very pure sources and a 4pi proportional gas counter to detect the decay positrons. Our result for the half-life is 1.17992(34) s. As a byproduct of this measurement, we determined the half-life of its daughter, 30P, to be 2.501(2) min.

RADIONUCLIDE AND MAJOR ELEMENT ANALYSIS OF THERMAL AND MINERAL WATERS IN CROATIA WITH A RELATED DOSE ASSESSMENT.

Major elements concentrations (Na, K, Ca, Mg) and the activity concentrations of 226,228Ra, 234,238U, 210Po, 210Pb, 40K and 137Cs in northern and eastern Croatian thermal and mineral waters, collected directly from springs (or wells), are presented herein with total effective doses assessed for those waters that are considered as drinking 'cures' and are available for consumption. The methods used for radionuclide determination included alpha-particle spectrometry, gas-proportional counting and gamma-ray spectrometry, while the major element composition was determined by ICP-MS. The activity concentrations of all of the radionuclides were found to be below the guidance levels set by the WHO and EC Directive, with the exception of one water sample that measured 0.26 Bq L-1 of 228Ra. The effective ingestion dose assessment for the consumption of the so-called water 'cures' during 1, 2 or 4 weeks' time period throughout 1 year was well below the recommended 0.1 mSv for drinking water.

High-efficiency and low-background multi-segmented proportional gas counter for [formula omitted]-decay spectroscopy

A multi-segmented proportional gas counter (MSPGC) with high detection efficiency and low-background event rate has been developed for β-decay spectroscopy. The MSPGC consists of two cylindrically aligned layers of 16 counters (32 counters in total). Each counter has a long active length and small trapezoidal cross-section, and the total solid angle of the 32 counters is 80% of 4π. β-rays are distinguished from the background events including cosmic-rays by analyzing the hit patterns of independent counters. The deduced intrinsic detection efficiency of each counter was almost 100%. The measured background event rate was 0.11 counts per second using the combination of veto counters for cosmic-rays and lead block shields for background γ-rays. The MSPGC was applied to measure the β-decay half-lives of 198Ir and 199mPt. The evaluated half-lives of T1∕2=9.8(7) s and 12.4(7) s for 198Ir and 199mPt, respectively, were in agreement with previously reported values. The estimated absolute detection efficiency of the MSPGC from GEANT4 simulations was consistent with the evaluated efficiency from the analysis of the β-γ spectroscopy of 199Pt, saturating at approximately 60% for Qβ> 4 MeV.

Si-detectors with internal proportional charge amplification

The results of investigation of special strip and pixel detectors are presented. The possibility to achieve the internal amplification mode similar to proportional gas counters in a pixel detector made from n-type silicon is shown. An “amplified” peak at the energy 70 MeV with the energy resolution FWHM \ extasciitilde 10 MeV is visible on the α -spectrum of 238Pu (Eα = 5.5 MeV). The real internal amplification effect (with a gain of 20) has been demonstrated with the detectors made from p-silicon. In this case, the detector could be used as a spectrometric device even in the amplification mode. The most important result of our investigation is the feasibility of efficient decrease of energy registration threshold for ionizing radiation in Si devices at room temperature. This effect has been achieved in the measurement with a 55Fe source (Eγ = 5.9 keV).

A procedure for the sequential determination of radionuclides in soil and sediment samples

We present a new radiochemical procedure for the sequential determination of Sr, Am, Pu, Th and U radionuclides. For the validation, seven IAEA certified reference materials were analyzed for 239Pu, 240Pu, 241Pu, 238U and 232Th isotopes by ICP-MS, 243Am by alpha spectrometry and 90Sr by low level gas proportional counting. The sequential method was then used for determining the radionuclide profiles in one sediment core collected in the River Rhine, near Augst, downstream of the Swiss nuclear power plants.

High-precision half-life measurement for the superallowed Fermi β+ emitter Mg22

A high-precision half-life measurement for the superallowed Fermi $\beta^+$ emitter $^{22}$Mg was performed at the TRIUMF-ISAC facility using a 4$\pi$ proportional gas counter. The result of $T_{1/2} = 3.87400 \pm 0.00079$ s is a factor of 3 more precise than the previously adopted world average and resolves a discrepancy between the two previously published $^{22}$Mg half-life measurements.

Determination of specific alpha-emitting radionuclides (uranium, plutonium, thorium and polonium) in water using [Ba+Fe]-coprecipitation method

The indicative dose (ID) is one of the parameters established in the current European directive for water intended for human consumption. To determine the ID, it is necessary to know the activity concentration of: 238U, 234U, 226Ra, 210Po, 239,240Pu and 241Am. The existing methods to determine these radionuclides involve complex radiochemical separations (ionic exchange columns, extraction chromatography, etc.), followed by measurements with a semiconductor detector, laboratory procedures that are time-consuming and costly. As a lower cost alternative that reduces measuring and preparation times, avoids the need for a self-absorption correction and the use of tracers, and above all that can be used in any laboratory, methods based on liquid-liquid extraction and selective co-precipitation were developed. These methodologies offer high separation recovery and selectivity, and the measurements are made using a gas proportional counter or a solid ZnS(Ag) scintillation counter. The separation factor ranged between 91.4% and 100.0% for all alpha-emitting radionuclides across the different methods. The activity concentration for each method was computed through linear equations that represent the relationship between the activity and selectivity of the different alpha-emitting radionuclides. This mathematical procedure simplifies the radiochemical separations and provides more accurate activity concentrations. The results of the internal and external validation studies proved that the proposed method is suitable for determining 241Am, 226Ra, uranium, plutonium, thorium and 210Po in water samples.

A large high-efficiency multi-layered Micromegas thermal neutron detector

Due to the so-called 3He shortage crisis, many detection techniques used nowadays for thermal neutrons are based on alternative converters. Thin films of 10B or 10B4C are used to convert neutrons into ionizing particles which are subsequently detected in gas proportional counters, but only for small or medium sensitive areas so far. The micro-pattern gaseous detector Micromegas has been developed for several years in Saclay and is used in a wide variety of neutron experiments combining high accuracy, high rate capability, excellent timing properties and robustness. We propose here a large high-efficiency Micromegas-based neutron detector with several 10B4C thin layers mounted inside the gas volume for thermal neutron detection. The principle and the fabrication of a single detector unit prototype with overall dimension of ∼ 15 × 15 cm2 and a flexibility of modifying the number of layers of 10B4C neutron converters are described and simulated results are reported, demonstrating that typically five 10B4C layers of 1–2 μm thickness can lead to a detection efficiency of 20–40% for thermal neutrons and a spatial resolution of sub-mm. The design is well adapted to large sizes making possible the construction of a mosaic of several such detector units with a large area coverage and a high detection efficiency, showing the good potential of this novel technique.

Development of lightweight portable neutron survey meter

ABSTRACTWe have developed a lightweight portable neutron survey meter comprising a proportional gas counter containing a mixed gas of methane gas and nitrogen gas for measuring the ambient neutron dose equivalent H*(10) up to about 20 MeV neutrons intended for use in nuclear power plants, and accelerator facilities. Since no heavy polyethylene moderator is used, the survey meter is only about 2.2 kg in weight causing a weight reduction of 70% or more compared to that of the conventional moderated-type survey meter. The spectrum-weight function, G(E) is adopted for dose conversion.In order to evaluate the energy characteristics of the developed survey meter, mono-energetic neutron reference fields and continuous energy neutron reference fields were used. The evaluation was also carried out by the PHITS calculation. Although the neutron energy response to the mono-energetic neutron fields was highly deviated from the ambient dose equivalent H*(10) in keV energy region, the response to H*(10) showed very good agreement only within 25% to the continuous energy neutron fields which are close to the actual work-place neutron fields. The neutron energy response was also investigated for high energy quasi-mono-energetic neutron fields and showed much better results compared with those of conventional moderated-type neutron survey meters.

Radiological assessment of the decontaminated and decommissioned Korea Research Reactor-1 building

The radiation dose of the Korea Research Reactor-1 (KRR-1), which had been decontaminated and decommissioned following shut down in 1995, was evaluated to assess the possibility of reusing the building as a memorial hall. The KRR-1 holds symbolic significance as the first reactor in Korean nuclear history and is designated as a registered cultural property of Korea. Exposure scenarios for visitors and the building manager were evaluated to examine the radiological safety of the building. Radioactive contamination inside the KRR-1 building was measured using gamma survey meter, surface alpha and beta contamination monitor, low level gas proportional counter, and semiconductor detector. The exposure dose rate for real radioactivity measurement was calculated using the RESRAD-BUILD code and uncertainty analysis was performed. The radionuclides of 60Co, 137Cs, and 152Eu were in the ranges of 0.09–0.011, 0.005–0.041, and 0.013–0.097Bq/g, respectively, on the surface of the reactor building. The external dose rate in the reactor building in the first year of the measurement ranged from 1.05×10−7 to 3.76×10−6mSv/h. The maximum exposure doses on the building manager and visitors in the first year were 1.82×10−4 and 1.07×10−6mSv/y, respectively, satisfying the dose limit for unrestricted release of the building. Thus, the radiological safety of the KRR-1 building was confirmed.