Beta-gamma Coincidence Counting Research Articles

A multi-channel beta–gamma coincidence counting system using well-HPGe and plastic scintillation detectors for radioactive Xenon measurements

Abstract A new type of multi-channel beta–gammacoincidence counting system was developed for the analysis of radioactive Xenon samples with low-level radioactivity . The proposed system consists of a state-of-the-art well-HPGe detector with a large well volume ( ∅ 28 mm × 40 mm) and a cylindrical plastic scintillation detector with an interior volume of 8.8 cm3. A two-dimensional beta–gamma coincidence histogram was obtained, and the beta–gamma coincidence counting efficiency was estimated using gaseous radioxenons and Monte Carlo simulation with the MCNP code. The energy resolution of the plastic scintillation detector for the 129.4 keV internal conversion electron was 29%, and the minimum detectable concentration for 131m Xe, 133Xe, 133m Xe, and 135Xe was calculated as 0.27 mBq/m3, 0.23 mBq/m3, 0.16 mBq/m3 and 0.24 mBq/m3 under the assumed conditions of a 20000 s measurement and a 10 m3 air sample with the beta–gamma​ coincidence mode, respectively.

Beta–gamma coincidence counting efficiency and energy resolution optimization by Geant4 Monte Carlo simulations for a phoswich well detector

A single-channel phoswich well detector has been assessed and analysed in order to improve beta-gamma coincidence measurement sensitivity of (131m)Xe and (133m)Xe. This newly designed phoswich well detector consists of a plastic cell (BC-404) embedded in a CsI(Tl) crystal coupled to a photomultiplier tube (PMT). It can be used to distinguish 30.0-keV X-ray signals of (131m)Xe and (133m)Xe using their unique coincidence signatures between the conversion electrons (CEs) and the 30.0-keV X-rays. The optimum coincidence efficiency signal depends on the energy resolutions of the two CE peaks, which could be affected by relative positions of the plastic cell to the CsI(Tl) because the embedded plastic cell would interrupt scintillation light path from the CsI(Tl) crystal to the PMT. In this study, several relative positions between the embedded plastic cell and the CsI(Tl) crystal have been evaluated using Monte Carlo modeling for its effects on coincidence detection efficiency and X-ray and CE energy resolutions. The results indicate that the energy resolution and beta-gamma coincidence counting efficiency of X-ray and CE depend significantly on the plastic cell locations inside the CsI(Tl). The degraded X-ray and CE peak energy resolutions due to light collection efficiency deterioration by the embedded cell can be minimised. The optimum of CE and X-ray energy resolution, beta-gamma coincidence efficiency as well as the ease of manufacturing could be achieved by varying the embedded plastic cell positions inside the CsI(Tl) and consequently setting the most efficient geometry.

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.

Simulation of Cherenkov photons emitted in photomultiplier windows induced by Compton diffusion using the Monte Carlo code GEANT4

The implementation of the TDCR method (Triple to Double Coincidence Ratio) is based on a liquid scintillation system which comprises three photomultipliers; at LNHB, this counter can also be used in the beta-channel of a 4pi(LS)beta-gamma coincidence counting equipment. It is generally considered that the gamma-sensitivity of the liquid scintillation detector comes from the interaction of the gamma-photons in the scintillation cocktail but when introducing solid gamma-ray emitting sources instead of the scintillation vial, light emitted by the surrounding of the counter is observed. The explanation proposed in this article is that this effect comes from the emission of Cherenkov photons induced by Compton diffusion in the photomultiplier windows. In order to support this assertion, the creation and the propagation of Cherenkov photons inside the TDCR counter is simulated using the Monte Carlo code GEANT4. Stochastic calculations of double coincidences confirm the hypothesis of Cherenkov light produced in the photomultiplier windows.

Radioactivity measurement and standardization in Thailand

An absolute measurement method for disintegration rates of radioisotopes by 4p beta-gamma coincidence counting systems is described. Absolute activity of 60Co and 99Mo was determined by the counting systems of Japan and Thailand. Radon gas measurement and standardization were also performed. A radon chamber was constructed and employed for the comparative measurements by a pulse-counting ionization chamber and an environmental-level scintillation chamber. The background radon concentration of the radon chamber was also determined.

Determining detection limits and minimum detectable concentrations for noble gas detectors utilizing beta-gamma coincidence systems

Beta-gamma coincidence counting is one of two acceptable noble gas monitoring measurement modes for Comprehensive Nuclear-Test-Ban-Treaty (CTBT) verification purposes defined in CTBT/PC/II/WG.B/1. Rigorous derivations of detection limits and minimum detectable activity concentrations for β-γ coincidence data are derived in this paper. Different sampling methodologies are modeled to show how the MDC is affected by different sample collection times, spectral collection times, background radon levels, and other factors.

Measurements of ambient radioxenon levels using the automated radioxenon sampler/analyzer (ARSA)

The Pacific Northwest National Laboratory has developed an Automated Radioxenon Sampler/Analyzer (ARSA) in support of the Comprehensive Nuclear-Test-Ban-Treaty (CTBT) to measure four radioxenon isotopes: 131mXe, 133mXe, 133gXe, and 135gXe. This system uses a beta-gamma coincidence counting detector to produce two-dimensional plots of gamma-energy versus beta-energy. Betas and conversion electrons (CE) are detected in a cylindrical plastic scintillation cell and gamma and X-rays are detected in a surrounding NaI(Tl) scintillation detector. The ARSA has been field tested at several locations to measure the radioxenon concentrations. Most recently it has been deployed at the Institut fur Atmospharische Radioaktivitat in Freiburg, Germany. During the first 4 months of 2000 the measured 133Xe oncentrations have varied between 0.0±0.1 and 110±10 mBq/m3 air. The longer lived 131mXe (T 1/2 = 11.9 d) and short lived 135Xe (T 1/2 = 9.1 h) have also been detected in small quantities, while 133mXe concentrations have been consistent with zero. Minimum detectable concentration (MDC) calculations for 133gXe fell well below the 1 mBq per standard-cubic-meter of air requirement adopted by the CTBT Preparatory Commission.1 A description of the radioxenon detector, the concentration and MDC calculations and preliminary results of the field test in Germany are presented.

Beta-gamma counting system for Xe fission products

A beta-gamma coincidence counting system has been developed for automated analysis of Xe gas samples separated from air. The Xe gas samples are contained in a cylindrical plastic scintillator cell located between two NaI(T1) scintillation detectors. The X-ray and gamma spectra gated by coincident events in the plastic scintillator cell are recorded for each NaI(T1) crystal. The characteristic signatures of the131mXe,133gXe,133mXe, and135gXe isotopes of interest for nuclear test-ban verification as well as the procedures and results of absolute efficiency measurements are described. A NaI(T1) crystal with provision for 4 sample cells has been implemented for the system to be deployed in the field. Examples of data on ambient air samples in New York City obtained with the field prototype are presented.

Standards for radioiodines.

The National Institute of Standards and Technology, NIST (formerly National Bureau of Standards), is the nation's standards laboratory for civilian technology. NIST develops and maintains the nation's physical measurement standards for medical therapy and diagnostics. For the past 50 years, NIST has developed radioactivity Standard Reference Materials (SRMs) for radioiodines as well as decay-scheme data and test methods for use by the radiopharmaceutical manufacturers in their quality assurance and quality control at the point of manufacture. Methods of standardizing radioiodines include 4 pi beta-gamma coincidence counting (131I), 4 pi beta-gamma anti-coincidence counting (129I), 4 pi(e,x)-gamma coincidence counting (123I), and x-gamma sum peak coincidence counting (125I). NIST also uses sources standardized by these techniques to calibrate re-entrant ionization chambers (dose calibrators) and scintillation counters. SRMs of 131I and 125I are now available on an annual basis, and the long-lived 129I has recently been reissued.

Standardization of selenium-75: some observations

An international intercomparison of activity measurements of a solution of selenium-75 was organized by the Bureau International des Poids et Mesures, France in May 1992. The solution was standardized by a 4π beta-gamma coincidence counting system using the efficiency extrapolation technique. The beta efficiency was varied by changing the high voltage of the proportional counter below the knee of the plateau, the absorber thickness and the solid content of the sources. The measurements were taken for two window settings of the γ-channel, namely, from 15 to 340 keV and 340 to 640 keV energies. The extrapolation was done by a linear least squares fit. It was found that the extrapolated values obtained by different methods differ by as much as 4%. The results of the measurements are discussed in detail. A correction factor for the metastable state was calculated using the most recent decay scheme parameters.

Pressure control of a pressurized proportional counter for 4 pi beta-gamma coincidence counting--effects of pressure variation and study of a non-flow type system

Effects of the pressure variation of counting gas on the efficiency function were examined using a 4 pi beta-gamma coincidence counting system with a pressurized proportional counter. The results showed that the pressure variation of about ten kPa could not give large effects on the efficiency function and that a non-flow type of pressurized proportional counter with a simple gas control system could work well in the case of the pressure higher than 1 MPa, an ordinary pressure for the counting.

Emission Probability of the 312-keV Gamma Ray from the Decay of Protactinium-233

The emission probability of the 312-keV gamma ray from the decay of 27-day 233Pa has been measured. A 4π beta-gamma coincidence counting system was used to determine the 233Pa sample disintegration...

The “SAMAR” shared-dead-time method. A new approach to beta-gamma coincidence counting

In a conventional β-γ coincidence counting system, the partially correlated β and γ series of pulses with their associated chain dead times, (τ β, τ γ), gives place to an overlapping process on the coincidence channel, whose transmission factor φ( A 0, τ β , τ γ ) becomes poorly defined for the general case. In this context, the “Shared-Dead-Time” (SDT) system has been conceived to impose a total time correlation between both chains blocking intervals by inserting simultaneously a common dead-time from a single paralysis generator which is triggered by the pooled counting pulses. As a result, identical transmission factors are obtained for the three counting channels. The extra cost in counting losses is well compensated by a good definition of dead-time for coincidences whose two first moments of its interval density get known. A novel dead-time circuit using fast linear gates as blocking elements and post-integration into the paralysis loop is introduced as an option for high count rates. The “SAMAR” instrumentation system incorporates a single “live-time” 1 MHz quartz clock and automatisms. The SDT system has been tested by Müller's two-oscillator method, slightly modified. Preliminary results proved the non-extending character of the new dead-time circuit and the qorking ability of the SDT two-branch loop.

Decay ofSc48

A previously unreported gamma ray of approximately 175 keV and 7% abundance was found in the decay of ${\mathrm{Sc}}^{48}$. This necessitates a revision of the decay scheme to include a second beta group with an end-point energy of approximately 475 keV. The presence of the new gamma and second beta group was confirmed by means of gamma-gamma and beta-gamma coincidence counting techniques.

The application of beta-gamma coincidence methods to radioisotopes with complex decay schemes

The applicability of beta-gamma coincidence counting to the determination of single radioisotopes with multiple decay schemes is demonstrated. An extension of this method to mixtures of radioisotopes is proposed and the necessary conditions are discussed.

Coincidence Counting of Special Samples

AbstractA beta-gamma coincidence counting technique was developed to analyze nuclide pairs such as Zr95-Nb95 and Ru103-Ru106 that are unresolvable by gamma spectrometry. The method provides a means of correcting the count rate for solids on the sample plate so that solids-free mounts or mounts on thin films are not required.

A 4π proportional counter suitable for 4π β-γ coincidence counting and routing use

A 4 pi proportional counter is described that is suitable for 4 pi beta-gamma coincidence counting and routine use. The counter exhibits good plateau and background characteristics and is safe and easy to use. An exploded diagram of the counter showing construction and internal arrangement is presented along with diagrams showing plateau characteristics. (N.W.R.)

Statistical errors in disintegration rate measurements by the coincidence technique

A simplified expression is developed for the fractional standard deviation as a function of the efficiencies of both detectors where the efficiency of one of the detectors can be made nearly equal to unity. The deviation is applicable to any form of the coincidence technique; however the case of 4 pi beta-gamma coincidence counting is considered. For simplicity, backgrounds and accidental coincidences are neglected. Their effects are usually small and can be calculated in the conventional manner. (N.W.R.)

Decay ofMg27

The gamma rays accompanying the decay of 9.45-min ${\mathrm{Mg}}^{27}$ have been studied by use of a NaI scintillation spectrometer and beta-gamma coincidence counting. Three gamma rays of energies 0.834, 1.015, and 0.175 Mev were found with relative intensities of 1.00, 0.43, and 0.009. The isotopic thermal-neutron activation cross section for production of ${\mathrm{Mg}}^{27}$ is found to be 25\ifmmode\pm\else\textpm\fi{}2 millibarns.