Gas Proportional Counter Research Articles

Effect of the nuclear medium onα-cluster excitation inLi6

The giant dipole resonance (GDR) in $^{6}\mathrm{Li}$ was investigated via the $^{6}\mathrm{Li}(\ensuremath{\gamma},xn)$ reactions by using quasi-mono-energy $\ensuremath{\gamma}$ rays in an energy range from 4.9 to 53.6 MeV. The $\ensuremath{\gamma}$ rays were generated via Compton backscattering of Nd laser photons with relativistic energy electrons in an electron storage ring, NewSUBARU. The energy resolution in a full width at half maximum of $\ensuremath{\gamma}$ ray was simulated to be $5%$ at 50 MeV. Photoneutrons were detected with a $4\ensuremath{\pi}$-type neutron detector consisting of 41 $^{3}\mathrm{He}$-gas proportional counters. The $(\ensuremath{\gamma},n)$ cross sections were dominant, while the $(\ensuremath{\gamma},2n)$ and $(\ensuremath{\gamma},3n)$ cross sections were negligibly small. The energy integral of photoneutron cross sections up to 53.6 MeV was 59 $\mathrm{MeV}\phantom{\rule{0.16em}{0ex}}\mathrm{mb}$, which exhausted $65%$ of the Thomas-Reiche-Kuhn sum rule. The GDR in $^{6}\mathrm{Li}$ was found to consist of mainly two components. The peak energy and the width for the low-energy component were ${E}_{r}=12\ifmmode\pm\else\textpm\fi{}1\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ and $\mathrm{\ensuremath{\Gamma}}=21\ifmmode\pm\else\textpm\fi{}2\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$. Those for the high-energy component were ${E}_{r}=33\ifmmode\pm\else\textpm\fi{}2\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ and $\mathrm{\ensuremath{\Gamma}}=30\ifmmode\pm\else\textpm\fi{}2$ MeV. The low-energy component corresponded to the GDR in $^{6}\mathrm{Li}$. The high-energy component was inferred to be the GDR owing to an $\ensuremath{\alpha}$-cluster excitation in $^{6}\mathrm{Li}$. The existence of this component was recently proposed and was suggested by the experimental studies of the $(p,{p}^{\ensuremath{'}})$, $(^{3}\mathrm{He},t)$, and $(^{7}\mathrm{Li},^{7}\mathrm{Be})$ reactions. The observed resonance shape of the high-energy component was well reproduced by modifying the GDR shape of a theoretical prediction for $^{4}\mathrm{He}$ at ${E}_{r}=26\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ with $\mathrm{\ensuremath{\Gamma}}=20\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$; with increasing the excitation energy by 7 MeV ($Q$ value was more negative), widening the width by $1.5\ifmmode\pm\else\textpm\fi{}0.1$ times, and decreasing a peak height by $0.29\ifmmode\pm\else\textpm\fi{}0.02$ times. As a result, the magnitude of the energy integral of the cross sections for the high-energy component observed in the present work was $0.86\ifmmode\pm\else\textpm\fi{}0.06$ times that in the theoretical prediction of the $^{4}\mathrm{He}(\ensuremath{\gamma},n)$ reaction. It is a well-known fact that a frequency of a vibrating system is inversely proportional to the size of the system. We suggest that in excitation of the $\ensuremath{\alpha}$ cluster in $^{6}\mathrm{Li}$, the mass of the $\ensuremath{\alpha}$ cluster increases by $7\ifmmode\pm\else\textpm\fi{}2\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$, the size of the $\ensuremath{\alpha}$ cluster in $^{6}\mathrm{Li}$ is smaller than that of the free $^{4}\mathrm{He}$ by $\ensuremath{\sim}20%$, and the width of the GDR is broader than that of $^{4}\mathrm{He}$ by 1.5 times owing to the nuclear medium effect.

Analytical method for the determination of gross beta, 90Sr, 226Ra and Pu isotopes in environmental samples

This study presents analytical methods for the determination of gross beta, 90Sr, 226Ra and Pu isotopes using samples in the IAEA-TEL-2015-04 ALMERA Proficiency Test exercise. Samples for gross beta were prepared by evaporation and then analyzed using a gas proportional counter. 90Sr in the liquid sample was concentrated as SrCO3 precipitates and purified by Sr resin. Pu isotopes and 90Sr in the soil sample were extracted from the sample by mineral acid leaching and separated using TEVA and Sr resin, respectively. Pu isotopes were determined by alpha spectrometry and 90Sr were determined with a liquid scintillation counter. Radium in the soil sample was extracted by LiBO2 fusion, and the radon-emanation method using LSC was applied for the determination of 226Ra.

Measurement of the gamma-ray energy spectrum of the educational Kinki University Reactor (UTR-KINKI)

The gamma-ray energy spectrum of the Kinki University Reactor (UTR-KINKI) was estimated from Ge detector measurements combined with Monte Carlo N-particle transport criticality calculations. The gamma rays mainly originated from prompt fission components, although small amounts of gamma rays from (n,γ) reactions, fission product gamma rays, and activation gamma rays were detected. The averaged gamma-ray tissue kerma rate in the irradiation port during UTR-KINKI operation at 1W was calculated as 10.5cGy/h based on the estimated gamma-ray energy spectrum. This value is consistent with a previous measurement with paired ionization chambers and a tissue equivalent gas proportional counter. This result demonstrates the reliability of the estimated gamma-ray energy spectrum.

10B+ZnS(Ag) as an alternative to 3He-based detectors for Radiation Portal Monitors

Typical radiation portal monitor systems, RPM, deployed to detect illicit trafficking of radioactive materials include a set of gamma-ray detectors and neutron detectors. Usually the employed neutron detectors are pressurized 3 He-based neutron detectors tubes. Due the shortage of 3 He reported since 2009, the amount of 3 He available for use in gas proportional counter neutron detectors has become limited, while the demand has significantly increased, especially for homeland security applications. For this reason, many different alternatives are being investigated for its use in RPM systems. The aim of this work is to study a scintillation detector ZnS(Ag) mixed with highly enriched 10 B, 10 B+ZnS(Ag). Using Monte Carlo methods, MCNPX code, the response of two neutron detectors based on 10 B+ZnS(Ag), manufactured by BridgePort Instruments LLC with different geometries, were estimated by calculating the number of 10 B(n,α)7 Li reactions for 29 monoenergetic neutron sources. Measurements and models were made, and both detectors were compared. The importance of the distance with respect to the ground was studied. The response with a 252 Cf moderated neutron source (0.5 cm lead and 2.5 cm polyethylene) was calculated in order to compare with other studied alternatives in the USA by Pacific National Northwest Laboratory, PNNL. With these results we conclude that neutron detectors using 10 B+ZnS(Ag) are an interesting alternative for replacing 3 He detectors. From the analysis with MCNPX we propose an improvement in the detector design.

A Gas Proportional Scintillation Counter with krypton filling

A Gas Proportional Scintillation Counter filled with pure krypton was studied. Energy resolution below 10% for 5.9-keV X-rays was obtained with this prototype. This value is much better than the energy resolution obtained with proportional counters or other MPGDs with krypton filling. The krypton electroluminescence scintillation and ionisation thresholds were found to be about 0.5 and 3.5 kV cm−1bar−1, respectively.

High-photon-yield scintillation detector with Ar/CF4 and glass gas electron multiplier

The glass made gas electron multiplier (GEM) and Ar/CF4-gas-based gaseous detector is developed as a scintillation detector and ultra high photon yield is demonstrated. The light yield of a glass GEM (G-GEM)-based gaseous detector is estimated to be 85,000 photons/keV, which is three orders of magnitude brighter than inorganic scintillators. The radioluminescence spectrum peak appeared at around 620 nm, which matches the spectral response of commonly used photosensors such as photomultiplier tubes, photodiodes, CMOSs, CCDs, and other photo-sensors. In X-ray spectroscopy, the light yield showed excellent proportionality and the device was successfully operated as a gas proportional scintillation counter. With this design, we obtained a high photon yield of the G-GEM, which has the further advantage of being much more sensitive to low-energy radiation than solid-scintillator-based detectors.

A rapid sequential separation of actinides and radiostrontium coupled to ICP-MS and gas proportional counting

A new protocol designed for the rapid determination of U, Th, Pu, Np, Am and Sr in up to 500 mL of river water samples has been developed. The new method employs chromatographic separation, using TEVA, TRU and Sr resins, coupled to an inductively coupled plasma mass spectrometry and to a gas proportional counting (GPC). Excellent figures of merit characterized by recoveries and accuracies exceeding 80 and 90 %, respectively and detection limits below emergency thresholds are obtained. The new GPC methodology for the quantification of radiostrontium led to accurate results even with activity ratios (A89Sr/A90Sr) as high as 95.

First results of a simultaneous measurement of tritium and 14C in an ultra-low-background proportional counter for environmental sources of methane

Simultaneous measurement of tritium and 14C would provide an added tool for tracing organic compounds through environmental systems and is possible via beta energy spectroscopy of sample-derived methane in internal-source gas proportional counters. Since the mid-1960's atmospheric tritium and 14C have fallen dramatically as the isotopic injections from aboveground nuclear testing have been diluted into the ocean and biosphere. In this work, the feasibility of simultaneous tritium and 14C measurements via proportional counters is revisited in light of significant changes in both the atmospheric and biosphere isotopics and the development of new ultra-low-background gas proportional counting capabilities for small samples (roughly 50 cc methane). A Geant4 Monte Carlo model of a Pacific Northwest National Laboratory (PNNL) proportional counter response to tritium and 14C is used to analyze small samples of two different methane sources to illustrate the range of applicability of contemporary simultaneous measurements and their limitations. Because the two methane sources examined were not sample size limited, we could compare the small-sample measurements performed at PNNL with analysis of larger samples performed at a commercial laboratory. These first results show that the dual-isotope simultaneous measurement is well matched for methane samples that are atmospheric or have an elevated source of tritium (i.e. landfill gas). However, for samples with low/modern tritium isotopics (rainwater), commercial separation and counting is a better fit.

A model for the secondary scintillation pulse shape from a gas proportional scintillation counter

Proportional scintillation counters (PSCs), both single- and dual-phase, can measure the scintillation (S1) and ionization (S2) channels from particle interactions within the detector volume. The signal obtained from these detectors depends first on the physics of the medium (the initial scintillation and ionization), and second how the physics of the detector manipulates the resulting photons and liberated electrons. In this paper we develop a model of the detector physics that incorporates event topology, detector geometry, electric field configuration, purity, optical properties of components, and wavelength shifters. We present an analytic form of the model, which allows for general study of detector design and operation, and a Monte Carlo model which enables a more detailed exploration of S2 events. This model may be used to study systematic effects in current detectors such as energy and position reconstruction, pulse shape discrimination, event topology, dead time calculations, purity, and electric field uniformity. We present a comparison of this model with experimental data collected with an argon gas proportional scintillation counter (GPSC), operated at 20 C and 1 bar, and irradiated with an internal, collimated 55Fe source. Additionally we discuss how the model may be incorporated in Monte Carlo simulations of both GPSCs and dual-phase detectors, increasing the reliability of the simulation results and allowing for tests of the experimental data analysis algorithms.

Optimization of simultaneous tritium–radiocarbon internal gas proportional counting

Specific environmental applications can benefit from dual tritium and radiocarbon measurements in a single compound. Assuming typical environmental levels, it is often the low tritium activity relative to the higher radiocarbon activity that limits the dual measurement. In this paper, we explore the parameter space for a combined tritium and radiocarbon measurement using a natural methane sample mixed with an argon fill gas in low-background proportional counters of a specific design. We present an optimized methane percentage, detector fill pressure, and analysis energy windows to maximize measurement sensitivity while minimizing count time. The final optimized method uses a 9-atm fill of P35 (35% methane, 65% argon), and a tritium analysis window from 1.5 to 10.3keV, which stops short of the tritium beta decay endpoint energy of 18.6keV. This method optimizes tritium-counting efficiency while minimizing radiocarbon beta-decay interference.

Shielding concepts for low-background proportional counter arrays in surface laboratories

Development of ultra low background gas proportional counters has made the contribution from naturally occurring radioactive isotopes – primarily α and β activity in the uranium and thorium decay chains – inconsequential to instrumental sensitivity levels when measurements are performed in above ground surface laboratories. Simple lead shielding is enough to mitigate against gamma rays as gas proportional counters are already relatively insensitive to naturally occurring gamma radiation. The dominant background in these surface laboratory measurements using ultra low background gas proportional counters is due to cosmic ray generated muons, neutrons, and protons. Studies of measurements with ultra low background gas proportional counters in surface and underground laboratories as well as radiation transport Monte Carlo simulations suggest a preferred conceptual design to achieve the highest possible sensitivity from an array of low background gas proportional counters when operated in a surface laboratory. The basis for a low background gas proportional counter array and the preferred shielding configuration is reported, especially in relation to measurements of radioactive gases having low energy decays such as 37Ar.

Energy Dependent Efficiency in Low Background Alpha Measurements and Impacts on Accurate Alpha Characterization

A difference in low emissivity alpha particle measurements for the same samples was observed between an Alpha Sciences model 1950 gas proportional counter and the XIA UltraLo-1800 ionization chamber. The energy dependent efficiency was evaluated for each instrument to reconcile the difference, and the implication of instrument design bias on measurement results is presented.

Simulations of electron avalanches in an ultra-low-background proportional counter

New classes have been added to the simulation package Garfield++ to import the potential and electric field solutions generated by ANSYS ® MaxwellTM v.16. Using these tools we report results on the simulation of electron avalanches and induced signal waveforms in comparison to experimental data of the ultra-low-background gas proportional counters being developed at Pacific Northwest National Laboratory. Furthermore, an improved mesh search algorithm based on Delaunay triangulation was implemented and provided at least a three order of magnitude time savings when compared to the built-in point-location search class of Garfield++.

High-precision half-life measurements for the superallowed Fermiβ+emitterNe18

The half-life of the superallowed Fermi β+ emitter Ne18 has been determined via two high-precision β counting experiments at TRIUMF's Isotope Separator and Accelerator facility. Using two different 4π continuous-flow gas-proportional counters, two independent measurements were made, yielding a weighted average of T1/2=1.66400−0.00048+0.00057 s, which is consistent with but approximately 2 times more precise than a previous high-precision measurement based on γ-ray counting. The present work achieves ±0.034% precision for the Ne18 half-life and will enable the inclusion of Ne18 among the set of precisely measured superallowed Fermi β-decay ft values once improved measurements are made for its Q value and superallowed branching ratio. As a test of systematic uncertainties, the half-life of Ne23 was measured and the world average has been improved, by a factor of 1.7, to 37.148±0.032 s.7 MoreReceived 1 June 2015DOI:https://doi.org/10.1103/PhysRevC.92.025502©2015 American Physical Society

Broad energy range neutron spectroscopy using a liquid scintillator and a proportional counter: Application to a neutron spectrum similar to that from an improvised nuclear device

A novel neutron irradiation facility at the Radiological Research Accelerator Facility (RARAF) has been developed to mimic the neutron radiation from an Improvised Nuclear Device (IND) at relevant distances (e.g. 1.5km) from the epicenter. The neutron spectrum of this IND-like neutron irradiator was designed according to estimations of the Hiroshima neutron spectrum at 1.5km. It is significantly different from a standard reactor fission spectrum, because the spectrum changes as the neutrons are transported through air, and it is dominated by neutron energies from 100keV up to 9MeV. To verify such wide energy range neutron spectrum, detailed here is the development of a combined spectroscopy system. Both a liquid scintillator detector and a gas proportional counter were used for the recoil spectra measurements, with the individual response functions estimated from a series of Monte Carlo simulations. These normalized individual response functions were formed into a single response matrix for the unfolding process. Several accelerator-based quasi-monoenergetic neutron source spectra were measured and unfolded to test this spectroscopy system. These reference neutrons were produced from two reactions: T(p,n)3He and D(d,n)3He, generating neutron energies in the range between 0.2 and 8MeV. The unfolded quasi-monoenergetic neutron spectra indicated that the detection system can provide good neutron spectroscopy results in this energy range. A broad-energy neutron spectrum from the 9Be(d,n) reaction using a 5MeV deuteron beam, measured at 60 degrees to the incident beam was measured and unfolded with the evaluated response matrix. The unfolded broad neutron spectrum is comparable with published time-of-flight results. Finally, the pair of detectors were used to measure the neutron spectrum generated at the RARAF IND-like neutron facility and a comparison is made to the neutron spectrum of Hiroshima.

Lineal energy calibration of a spherical TEPC.

Tissue-equivalent proportional counters (TEPCs) do not always allow built-in calibration alpha-particle sources, and the lineal energy calibration of these counters must be performed with an external radiation able to penetrate the detector walls. The irradiation field can be used for calibration if a particular marker point of known lineal energy is identified in the measured spectrum. This point is often identified with the proton edge, which corresponds to the maximum energy deposited by protons in the given volume. If the proton edge cannot be identified precisely in the measured spectrum, a gamma source can be used instead, identifying the maximum lineal energy due to electrons (e-edge). The technique was already described and applied for cylindrical TEPCs, allowing a calibration with an overall uncertainty smaller than 5 % (Conte et al. Lineal energy calibration of mini tissue equivalent gas-proportional counters (TEPC). AIP Conf. Proc. 1530, 171-178 (2013)). In the present work, this study was repeated for spherical detectors. First a marker point was identified in the microdosimetric spectrum of a (137)Cs gamma source, then a precise value of lineal energy was assigned to it. Gas pressures were varied to simulate diameters from 0.5 and 3 µm at density 1 g cm(-3). A simple power equation is given for allowing calibration of TEPCs filled with C3H8-TE gas at different pressures, using an external (137)Cs gamma source.

A modeling tool for detector resolution and incomplete charge collection

The detector response function of X‐ray and gamma‐ray detectors is obtained from the convolution of the energy deposition spectrum with the detector resolution function. The energy deposition spectrum can be computed by using deterministic or Monte Carlo codes, while the energy resolution depends specifically on the detection mechanism, which is characteristic of the single detector. In a first approximation, the energy resolution can be modeled using a normalized Gaussian distribution having its full width at half maximum expressed in terms of specific semiempirical formulas for solid‐state detectors, scintillators, and gas proportional counters. However, this approach is not sufficient with some solid‐state detectors. It is frequent to find that the peaks show a deviation from the Gaussian shape: a long flat shelf structure from the peak centroid to the lower energies and an asymmetry that can be described with an exponential decay on the left side of the peak. These two effects have been introduced in the new tool RESOLUTION by adapting empirical models found in literature. RESOLUTION can be tailored to the specific detector by analyzing measured monochromatic peaks by means of the following strategies: (1) in a first approximation, a Gaussian shape is assumed in order to determine the full width at half maximum parameters, (2) if it is noted a flat background on the left side of the peak, then a shelf function is added, and (3) if a departure of the Gaussian is observed, then an exponential tail function is added. RESOLUTION gives a very precise description of the line shape. Copyright © 2015 John Wiley & Sons, Ltd.

Effect of Air on Energy and Rise-Time Spectra Measured by Proportional Gas Counter

Air exerts a negative effect on radiation detection using a gas counter because oxygen contained in air has a high electron attachment coefficient and can trap electrons from electron-ion pairs created by ionization from incident radiation in counting gas. This reduces radiation counts. The present study examined the influence of air on energy and rise-time spectra measurements using a proportional gas counter. In addition, a decompression procedure method was proposed to reduce the influence of air and its effectiveness was investigated. For the decompression procedure, the counting gas inside the gas counter was decompressed below atmospheric pressure before radiation detection.For the spectrum measurement, methane as well as various methane and air mixtures were used as the counting gas to determine the effect of air on energy and rise-time spectra. Results showed that the decompression procedure was effective for reducing or eliminating the influence of air on spectra measurement using a proportional gas counter.

One-Year-Long Continuous and Synchronous Data Set of Fossil Carbon in Atmospheric PM2.5 and Carbon Dioxide in Debrecen, Hungary

Radiocarbon investigation of atmospheric PM2.5 aerosol synchronized with 14CO2 observations began in Debrecen in the winter of 2010. The aim of the study was to determine the contemporary and fossil carbon fractions in the aerosol and to set them against the fossil CO2 excess data referring to the same period. The mass of the collected PM2.5 mode on prebaked quartz filters was determined gravimetrically, while its total carbon mass was calculated from the pressure of CO2 gas produced after the combustion of the filters. As a result of the applied sampling and preparation method, the stable, nonvolatile carbon forms were principally studied. 14C measurements of the tiny aerosol bulk samples were performed using the EnvironMICADAS accelerator mass spectrometer at ATOMKI. The sample preparation method was tested using several blanks, standards, and real samples. Test results showed good reproducibility for the applied aerosol sample preparation and accelerator mass spectrometry (AMS) 14C analyses. Atmospheric fossil CO2 excess data were calculated according Levin et al. (2003), using the 14C results of collected CO2 samples measured by the gas proportional counting system at ATOMKI. Mass concentration of PM10 involving the PM2.5 mode in the city air exceeded the daily average of 50 μg/m3 (24-hr limit value in the EU) several times in 2011, mainly during the winter. The results showed that recently derived carbon most likely from domestic wood burning was causing the elevated carbon mass concentration of PM2.5 in Debrecen at the time. In the course of the 1-yr-long continuous and systematic comparison of fossil carbon mass concentration of PM2.5 mode and mole fraction of fossil excess of atmospheric CO2, similar and synchronous trends were observed during the studied period in Debrecen.

High-gain effects minimized at the ends of the anodes in position sensitive gas proportional counters for SSM on ASTROSAT

The Scanning Sky Monitor (SSM) on ASTROSAT is a position-sensitive gas-filled proportional counter with a wide field of view. The science objective of SSM is to scan the sky to detect and locate transient X-ray sources in the outburst phase. The energy range of operation of SSM is 2.5 to 10 keV. Gas-filled proportional counters are known to have distorted electric fields at the ends of the anodes inside the detector. The electric field and hence the gas gain is different at the ends of the anodes compared to that of the central region. In SSM, the ends of the anode wires were found to have high electric field values and hence high gas gain initially. These effects had to be minimized as they would result in huge charge collection for incidence of highly energetic photons and charged particles, leading to probable discharge effects which would limit the life time of the detector. They also result in undesirable signals, the amplitude of which may not be proportional to the energy of the incident photon. In this paper, we discuss the technique which we use to reduce the field at the ends of the anodes in SSM detectors.