Geant4 Monte Carlo radioxenon beta-gamma coincidence efficiency simulation for a phoswich detector

In this work, a Monte Carlo (MC) simulation model is established to accurately characterize a phoswich beta-gamma coincidence detector system. This model can be easily used to predict the beta-gamma coincidence efficiencies of xenon radioisotopes at various stable xenon concentrations in the counting cell. The results demonstrate that there is a significant inverse correlation between beta-gamma coincidence efficiency and stable xenon concentration. The influence of stable xenon concentration on beta-gamma coincidence counting efficiency has been investigated for each individual xenon radioisotope. The results indicate that the effect of stable xenon concentration on beta-gamma coincidence efficiency depends on the xenon radioisotope and its decay modes. The coincidence efficiency of ¹³³Xe with 31.0-keV X-ray decay mode is the most affected one; and then followed by ^131mXe, ¹³³Xe with 81.0-keV gamma-ray decay mode, ^133mXe and finally ¹³⁵Xe. The study also indicates that the gamma absorption by xenon gas plays more of a role in the decrease of beta-gamma coincidence efficiency for ¹³³Xe and ¹³⁵Xe, and that the conversion electron spectrum shifting and broadening plays more of a role in the reduction of beta-gamma coincidence efficiency for the metastable radioxenon of ^131mXe and ^133mXe.     

A well-type phoswich detector for nuclear explosion monitoring

In this work, a well-type phoswich detector with three scintillation layers has been designed and tested for measuring atmospheric xenon radioisotopes in order to monitor nuclear explosions. The detector was made by optically coupling three concentric cylindrical scintillation layers (BC-400, CsI(Tl) and BGO) to a single photomultiplier tube. Beta-gamma coincidence technique was used to detect beta particles and gamma rays. Other important features of this detector are its Compton suppression capability and simple, compact and cost effective design. Our calculations and measurements with the well-type phoswich detector show that the minimum detectable concentrations are close to or below 1 mBq/m³ for the four xenon radioisotopes.     

Comparison of phoswich and ARSA-type detectors for radioxenon measurements

The monitoring of atmospheric radioxenon to ensure compliance with the Comprehensive Nuclear Test Ban Treaty (CTBT) has driven the development of improved detectors for measuring xenon, including the development of a phoswich detector. This detector uses only one PMT to detect β–γ coincidence, thus greatly reducing the bulk and electronics of the detector in comparison to the ARSA-type detector. In this experiment, ¹³⁵Xe was produced through neutron activation and a phoswich detector was used to attain spectra from the gas. These results were compared to similar results from an ARSA-type β–γ coincidence spectrum. The spectral characteristics and resolution were compared for the coincidence and beta spectra. Using these metrics, the overall performance of the phoswich detector for β–γ coincidence of radioxenon was evaluated.     

A compton-suppressed phoswich detector for gamma spectroscopy

A phoswich detector with two scintillation layers has been designed and assembled at Oregon State University. This detector is able to identify and reject Compton events and ultimately reduce the Compton continuum in gamma energy spectra. In this detector, CsI(Tl) crystal is used to primarily detect photoelectric events. The CsI(Tl) crystal is partially surrounded by a BGO crystal layer to capture and identify Compton-scattered photons. Both crystals are optically coupled to a single photomultiplier tube. A real-time, FPGA-based digital pulse shape analysis was developed to discriminate and reject Compton-induced pulses from the CsI(Tl) crystal. All the digital pulse processing functions including pulse shape discrimination analysis, pile-up rejection and energy measurement were implemented in an on-board FPGA device. In this paper, the results of recent measurements using radioactive lab sources will be presented and discussed.     

Environmental applications of stable xenon and radioxenon monitoring

Characterization of transuranic waste is needed for decisions about waste site remediation. Soil-gas sampling for xenon isotopes can be used to define the locations of spent fuel and transuranic waste. Radioxenon in the subsurface is characteristic of transuranic waste and can be measured with extreme sensitivity using large-volume soil-gas samples. Measurements at the Hanford Site showed ¹³³Xe and ¹³⁵Xe levels indicative of ²⁴⁰Pu spontaneous fission. Stable xenon isotopic ratios from fission are distinct from atmospheric xenon background. Neutron capture by ¹³⁵Xe produces an excess of ¹³⁶Xe in reactor-produced xenon, providing a means of distinguishing spent fuel from separated transuranic material.     

Contribution to the development of atmospheric radioxenon monitoring

Within the frame of Comprehensive Nuclear-Test Ban Treaty (CTBT), this paper deals with the development of the new techniques necessary for the xenon monitoring requested by the CTBT. An automatic system called SPALAX™, devoted to the on-site sampling and measurement was developed by French atomic energy commission (CEA). Analytical methods and equipments have been studied at our laboratory, using dual X-γ-spectrometry in order to get independent means with better sensitivity within a robust quality assurance program. In the case of a wide number of potential existing sources and depending on meteorological conditions, several solutions can be arrived at.     

A review of the developments of radioxenon detectors for nuclear explosion monitoring

Journal of Radioanalytical and Nuclear Chemistry - Developments in radioxenon monitoring since the implementation of the International Monitoring System are reviewed with emphasis on the most...     

A radioxenon detection system using PIPS and CZT

Journal of Radioanalytical and Nuclear Chemistry - This paper introduces and describes the initial characterizations of a prototype beta-gamma coincidence detection system that utilizes a PIPSBox...     

Development of a neutron beam line and detector system for multiple prompt gamma-ray analysis

A neutron beam line for multiple prompt gamma-ray analysis was constructed at the Japan Atomic Energy Agency. A detector system for the MPGA was constructed at the C2-3-2 beam line in January 2005. It comprised eight (upgraded in March 2007) clover Ge detectors with a BGO Compton suppressor. High efficiency detector system provides an advantage in terms of the detection limit of MPGA when compared to the result of PGA. The supermirror neutron bender was improved and a supermirror neutron guide was installed upstream of the sample position.     

Development of a universal Raman detector for microchromatography

Summary A detector for microchromatography in which Raman spectroscopy is used to identify the eluted species has been developed. The detector is designed to be applicable to a wide range of compounds without requiring the presence of a chromophore. Its use is illustrated in the analysis of nitro compounds on a 250 μm i.d. column. Raman spectra of each of the compounds could be identified as they passed the detector. The advatages of the use of fully deuterated solvents are demonstrated by the analysis of nitrobenzenes in methanol/water mobile phases. The detection limit for nitrobenzene using the Raman line at 1342 cm⁻¹ was 75ng.     

Development of a detection tablet for a portable NO2 monitoring system.

We have already developed a HCHO monitoring system which is called FP-30. In this experiment, we have developed a NO(2) detection tablet which can be used by the monitoring system. The detection tablet for the NO(2) was constructed with the sensing paper: porous cellulose paper that contains silica gel as an adsorbent, N-1-naphthylethylenediamine dihydrochloride (NED), and glycerin. The NO(2) in sample gas was blown over and adsorbed on the surface of the sensing paper. Then the NO(2) reacted with NED, producing a yellow compound. The coloring reaction took place on the surface of the sensing paper. The degree of color change of paper from white to yellow was monitored as a function of the intensity of the reflected light (lambda = 475 nm) of an LED. The detection limit was 0.01 ppm when the sampling time was 30 min, and the flow rate of sample gas was 250 ml/min. This sensing paper process was not interfered with by acetaldehyde, acetone, alcohols, hydrocarbons, carbon monoxide or carbon dioxide. The NO(2) concentrations in the rooms of a house or school were monitored using this monitoring system and the standard chemiluminescence method. The concentrations of NO(2) monitored by both methods were within 18% of the average. This highly sensitive, selective, and handy NO(2) gas monitoring system will be widely applicable and convenient for users who are not specialists in this field.     

Bioelectronic detector with monoamine oxidase for halitosis monitoring

Methyl mercaptan (MM) is known as one of the major chemicals of halitosis (bad breath). In this study, a bioelectronic gas sensor (bio-detector) for gaseous MM was developed and was applied to measure halitosis in breath. The bio-detector consisted of a Clark-type dissolved oxygen electrode, a monoamine oxidase type-A (MAO-A) immobilized membrane and a reaction unit that had liquid and gaseous compartments separated by a hydrophobic porous polytetrafluoroethylene (PTFE) diaphragm membrane. The tip of the electrode covered with MAO-A membrane was placed into the liquid compartment as touching to the PTFE diaphragm membrane. In order to amplify the bio-detector output, a substrate regeneration cycle caused by coupling the monooxygenase with l-ascorbic acid as reducing reaction with reagent system, was applied. The results of MM vapor measurements showed the calibration range of the bio-detector for MM vapor was from 0.087 to 11.5 ppm (correlation coefficient: 0.993) and included the human sense of smell level 5 (0.2 ppm). The bio-detector had good selectivity being attributed to enzyme specificity was obtained for several substances (trimethyl amine, ammonia, dimethyl sulfide, etc.). The bio-detector was applied for halitosis measurement. Expired gases in five subjects were sampled every hour and the concentrations of MM in the expired gases were monitored. The output of bio-detector showed behaviour of halitosis level changes in a day such as increasing with passage of time and decreasing after eating.     

Development of a novel neutron detector for imaging and analysis

A hardware system employing dynamic Random Access Memory (dRAM) has been designed to make possible the detection of neutrons. One recognised difficulty with dynamic memory devices is the alpha-particle problem. That is alpha-particle contamination present within the dRAM encapsulating material may interact sufficiently as to corrupt stored data. We essentially utilized the fact that these corruptions, known as soft errors, may be induced in dRAMs by the interaction of charged particles with the chip itself as a basis for system function. A preliminary feasibility study has been carried out to use dynamic RAMs as alpha-particle detectors. Our initial system tests provide information upon detection efficiency, soft error reading rate, energy dependence of the soft error rate and the soft error operating bias relationship. These findings highlight the usefulness of such a device in neutron dosimetry, imaging and analysis, by using a neutron converter with a high cross section for the (n, ) capture reaction.     

Study of silicon detectors for high resolution radioxenon measurements

Measurement of radioactive xenon in the atmosphere is one of several techniques to detect nuclear weapons testing, typically using either scintillator based coincidence beta/gamma detectors or germanium based gamma only detectors. Silicon detectors have a number of potential advantages over these detectors (high resolution, low background, sensitive to photons and electrons) and are explored in this work as a possible alternative. Using energy resolutions from measurements and detection efficiencies from simulations of characteristic electron and photon energies, the minimum detectable concentration for Xe isotopes was estimated for several possible detector geometries. Test coincidence spectra were acquired with a prototype detector.     

Development of a solid surface fluorescence-based sensing system for aluminium monitoring in drinking water

A novel, single and robust solid surface fluorescence-based sensing device assembled in a continuous flow system has been developed for the determination of trace amounts of aluminium in water samples. The proposed method is based on the transient immobilization of the target species on an appropriate active solid sensing zone (C₁₈ silica gel). The target species was the fluorogenic chelate, formed as a result of the on-line complexation of Al(III) with chromotropic acid (CA) at pH 4.1. The fluorescence of the complex is continuously monitored at an emission wavelength of 390 nm upon excitation at 361 nm. The instrumental, chemical and flow-injection variables affecting the fluorescence signal were carefully investigated and optimized. After selecting the most suitable conditions, the sensing system was calibrated in the range 10–500 μg l⁻¹, obtaining a detection limit of 2.6 μg l⁻¹, and a R.S.D. of 2.2%, with a sampling frequency of 24 h⁻¹. In addition, the selectivity of the proposed methodology was evaluated by performing interference studies with different cations and anions which could affect the analytical response. Finally, the proposed method, which meets the EU regulations regarding the aluminium content in drinking waters, was satisfactorily applied to different water samples, with recoveries between 97 and 105%. The simplicity, low cost and easy operation are the main advantages of the present procedure.     

Development of a monitoring system for vinyl chloride gas in air by using an HCl monitoring tape and pyrolyzer

A continuous monitoring system for vinyl chloride gas in air has been developed using an HCl monitoring tape and pyrolyzer consisting of a heater around a quartz tube. It is based on the color change of the tape by reaction with HCl gas produced by decomposition of vinyl chloride gas in the heated quartz tube. The conversion efficiency of vinyl chloride into HCl depends on the temperature of the pyrolyzer. The tape impregnated with a coloring solution that includes Metanil Yellow (pH indicator; pH 1.2-2.3, red-yellow), glycerin and methanol is a highly sensitive means of detecting HCl gas. When vinyl chloride gas was passed through the heated quartz tube (910 degrees C) and the HCl gas produced was passed through the tape, the color of the tape changed from yellow to red. The degree of color change was proportional to the concentration of vinyl chloride gas with a constant sampling time and flow rate. The degree of color change could be recorded by measuring the intensity of reflecting light (555 nm). This method is scarcely affected by other gases with the exception of chlorinated hydrocarbons such as trichloroethylene and chloroform or strong acids such as HCl gas. Reproducibility tests showed that the relative standard deviation of the relative intensity (n = 10) was 4.5 for 5 ppm vinyl chloride. The detection limit was 0.4 ppm for vinyl chloride with a sampling time of 40 s and a flow rate of 300 ml min (-1).     

A radioxenon detection system using CdZnTe,an array of SiPMs,and a plastic scintillator

This paper presents the design and characterization of a prototype compact beta–gamma radioxenon detection system that utilizes a coplanar CdZnTe crystal, an array of SiPMs, and a plastic scintillator. The detector is directly mounted on a custom PCB. The system provides the advantage of room-temperature operation, while being compact, low noise, and with simple readout electronics. Preliminary measurements using ¹³⁷Cs, ¹³⁵Xe, and ^133/133mXe were conducted to optimize various system parameters to achieve optimal resolution of key photopeaks. The purpose of this research was to explore the potential of these radiation detection elements for use in beta–gamma coincidence applications.     

Utilization of phoswich detectors for simultaneous,multiple radiation detection

Summary A phoswich radiation detector is comprised of a phosphor sandwich in which several different phosphors are viewed by a common photomultiplier. By selecting the appropriate phosphors, this system can be used to simultaneously measure multiple radiation types (alpha, beta, gamma and/or neutron) with a single detector. Differentiation between the signals from the different phosphors is accomplished using digital pulse shape discrimination techniques. This method has been shown to result in accurate discrimination with highly reliable and versatile digital systems. This system also requires minimal component count (i.e., only the detector and a computer for signal processing). A variety of detectors of this type have been built and tested including: (1) a triple phoswich system for alpha/beta/gamma swipe counting, (2) two well-type detectors for measuring low levels of low energy photons in the presence of a high energy background, (3) a large area detector for measuring beta contamination in the presence of a photon background, and (4) another large area detector for measuring low energy photons from radioactive elements such as uranium in the presence of a photon background. An annular geometry, triple phoswich system optimized for measuring alpha/beta/gamma radiation in liquid waste processing streams is currently being designed.     

A non-intrusive very high-frequency conductivity detector for continuous flow monitoring

A non-intrusive inductively-coupled conductance detector operating at 115 MHz is described. The flowing sample passes through a straight glass tube confined within the inductance coil of a parallel tuned high-Q circuit. Changes in Q caused by the resistive component of the sample are measured. Potassium chloride in water can be monitored down to 2 ppm with a linear response over three orders of magnitude of concentration.