Compton Suppression Research Articles

Comparison of two spectrometric counting modes for fast analysis of selected radionuclides activity

The two counting modes: a normal with a single HPGE detector and second with the additional anti-Compton shield of the annular NaI(Tl) detector have been compared for fast determination of the activity concentration of thorium 232Th in the building materials. The 232Th activity concentration was calculated by measurement of its decay products: 212Pb, 212Bi and 208Tl as well 228Ac content. Although the Compton suppression mode applied in gamma spectrometry systems in general increase sensitivity of the analysis, but in case of 583 keV the most abundant 208Tl γ-line, the significant reduction of photon counting rate was observed.

Erratum to: Measurement and simulation of a Compton suppression system for safeguards application

Erratum to: Measurement and simulation of a Compton suppression system for safeguards application

Development of an optimized Compton suppression gamma-ray spectrometric system using Monte Carlo simulation

We have chosen to establish the Compton Suppression Spectrometer (CSS) for low activity environmental samples with a high purity germanium (HPGe) primary detector and a removable plug-in detector (NaI(Tl)) surrounded with a cylindrical annulus guard detector (NaI(Tl)). Monte Carlo simulation with PENELOPE (PENetration and Energy LOss of Positrons and Electrons) is used to determine the optimal geometry of the CSS. To verify a correlation between experiment and simulation, the energy distribution of 137Cs and 60Co point sources is measured and simulated for each condition. The CSS parameters are studied to determine optimal detector geometry and Compton Suppression Factor (CSF). The timing resolution of the CSS was found to be 44ns (FWHM), which is an outstanding result in the semiconductor-based gamma-ray spectrometry. All measured values of CSF agree within 5% with the values obtained from the simulation. The optimum geometry and CSF values are discussed.

Application of the ML-EM algorithm in the suppression of Compton background of gamma-ray spectroscopy system

In the present study, the Compton background of the measured gamma-ray spectrum was suppressed by using the deconvolution method with applying the maximum likelihood fitting by expectation maximization (ML-EM) algorithm. The MATLAB program for deconvolution of the measured spectrum were written based on the applying of ML-EM algorithm in conjunction with a matrix of detector response functions within the energy range 0–1.9 MeV. The Compton Suppression Factor (SF) ratio of the deconvolved spectrum is increased by approximately 3–9 times relative to the measured spectrum of 137Cs and 60Cs, respectively. Additionally, the photopeak areas of deconvolved spectra were considerably raised to compare with ones of measured spectra owing to accumulating the counting numbers of the background into appropriate photopeaks.

Experimentally validated Monte Carlo simulation of an XtRa-NaI(Tl) Compton Suppression System response

In this work the response of an XtRa-NaI(Tl) Compton Suppression System is simulated using the Monte Carlo code PENELOPE. The main program PENMAIN is properly modified in order to couple two energy deposition detectors and simulate the coincidence gating. The modified main program takes into account both the active shielding and the True Coincidence phenomenon. The program is evaluated by comparing simulation results with experimental data for both non-cascade and cascade emitters and concluding that no statistically significant biases are observed.

Measurement and simulation of a Compton suppression system for safeguards application

Plutonium (Pu) contents in spent nuclear fuels, recovered uranium (U) or uranium/transuranium (U/TRU) products must be measured in order to secure the safeguardability of a pyroprocessing facility. Self-induced X-Ray fluorescence (XRF) and gamma-ray spectroscopy are useful techniques for determining Pu-to-U ratios and Pu isotope ratios of spent fuel. Photon measurements of spent nuclear fuel by using high-resolution spectrometers such as high-purity germanium (HPGe) detectors show a large continuum background in the low-energy region, which is due in large part to Compton scattering of energetic gamma rays. This paper proposes a Compton suppression system for reducing of the Compton continuum background. In the present study, the system was configured by using an HPGe main detector and a BGO (bismuth germanate: Bi4Ge3O12) guard detector. The system performances for gamma-ray measurement and XRF were evaluated by means of Monte Carlo simulations and measurements of the radiation source. The Monte Carlo N-Particle eXtended (MCNPX) simulations were performed using the same geometry as for the experiments, and considered, for exact results, the production of secondary electrons and photons. As a performance test of the Compton suppression system, the peak-to-Compton ratio, which is a figure of merit to evaluate the gamma-ray detection, was enhanced by a factor of three or more when the Compton suppression system was used.

Further investigation of epithermal neutron activation analysis in the determination of heavy metals in the Arctic atmosphere

We have further explored the use of epithermal NAA with Compton suppression to establish the presence of barium, potassium, strontium and zinc in Arctic air filters. Silver was determined using cyclic epithermal NAA in air filters. For one-sixteenth of a Whatman air filter detection limits for barium, potassium, silver strontium, and zinc were 5, 7, 0.01, 1 and 0.9 μg, respectively. Results revealed that longer counting times for the activation products of barium, strontium and zinc would be needed to consistently achieve uncertainties less than 20 %.

Fission product analysis of HEU irradiated within a boron carbide capsule: comparison of detection methodology at PNNL and AWE

The fission products from HEU formed under a fast-pooled neutron spectrum generated using a boron carbide shield were analyzed at Pacific Northwest National Laboratory and the Atomic Weapons Establishment. The results from each laboratory using chemical separation, high-purity germanium gamma spectroscopy and/or Compton suppression gamma spectroscopy are compared with the potential benefits and limitations of the different gamma spectroscopy methods discussed.

Compton background suppression with a multi-element scintillation detector using high speed data acquisition and digital signal processing

A multi-element scintillation detector, consisting of eight NaI(Tl)/BGO scintillators surrounding a single NaI(Tl)/CsI(Tl) scintillator, was initially developed for locating and measuring concealed special nuclear materials that emit primarily low energy photons. Signal digitizers and LabView virtual instrument (VI) subroutines process and analyze pulses from each of the dual scintillators to suppress Compton interactions occurring in the central detector and discriminate between low and high energy photon events occurring within NaI(Tl) and CsI(Tl) crystals, respectively. Digital signal processing significantly improved the signal-to-noise ratio of the central detector and greatly reduced the analog electronic equipment required in the same time.

Simulation of background reduction and Compton suppression in a low-background HPGe spectrometer at a surface laboratory

High-purity germanium (HPGe) detectors are well suited to analyse the radioactivity of samples. In order to reduce the environmental background for an ultra-low background HPGe spectrometer, low-activity lead and oxygen free copper are installed outside the probe to shield from gamma radiation, with an outer plastic scintillator to veto cosmic rays, and an anti-Compton detector to improve the peak-to-Compton ratio. Using Geant4 tools and taking into account a detailed description of the detector, we optimize the sizes of these detectors to reach the design requirements. A set of experimental data from an existing HPGe spectrometer was used to compare with the simulation. For the future low-background HPGe detector simulation, considering different thicknesses of BGO crystals and anti-coincidence efficiency, the simulation results show that the optimal BGO thickness is 5.5 cm, and the peak-to-Compton ratio of 40K is raised to 1000 when the anti-coincidence efficiency is 0.85. In the background simulation, 15 cm oxygen-free copper plus 10 cm lead can reduce the environmental gamma rays to 0.0024 cps/100 cm3 Ge (50 keV-2.8 MeV), which is about 10−5 of the environmental background.

Determination of Ag, Au, Cu and Zn in ore samples from two Mexican mines by various thermal and epithermal NAA techniques

Concentrations of Ag, Au, Cu and Zn were determined via neutron activation analysis in ore prospecting samples from the Cozamin and Tizapa Mexican mines. Ag concentrations were determined by applying cyclic epithermal neutron activation analysis. The method combined with an automated fast-pneumatic transfer system allows increased sample through-put which improves the analytical precision in silver prospecting. Combinations of thermal, epithermal and Compton suppression NAA were used to improve signal-to-noise ratios. Mining depths with significantly higher levels of Ag were determined. Reference material concentrations for quality control were found to be in good agreement with the certified values.

Tracing ancient silk route by nuclear-analytical technique

Total potassium content of archaeological artifacts like glass beads was determined by estimating the amount of 40K in the sample using Compton Suppression Spectroscopy which in turn unveiled the trading pattern in past through famous ancient silk route in the Bay of Bengal region. The developed technique neither involved any reactor/accelerator/X-ray source nor any chemical treatment of the samples. We analyzed eight different samples from Tamilnadu, India of which two samples showed elevated potassium content indicating their different origin. This is the first report to discriminate glass beads according to their potassium content, which ultimately helped to predict their origin.

Compton suppressed LaBr3 detection system for use in nondestructive spent fuel assay

Current methods for safeguarding and accounting for spent nuclear fuel in reprocessing facilities are extremely resource and time intensive. The incorporation of autonomous passive gamma-ray detectors into the procedure could make the process significantly less burdensome. In measured gamma-ray spectra from spent nuclear fuel, the Compton continuum from dominant fission product photopeaks obscure the lower energy lines from other isotopes. The application of Compton suppression to gamma-ray measurements of spent fuel may reduce this effect and allow other less intense, lower energy peaks to be detected, potentially improving the accuracy of multivariate analysis algorithms. Compton suppressed spectroscopic measurements of spent nuclear fuel using HPGe, LaBr3, and NaI(Tl) primary detectors were performed. Irradiated fuel was measured in two configurations: as intact fuel elements viewed through a collimator and as feed solutions in a laboratory to simulate the measurement of a dissolved process stream. These two configurations allowed the direct assessment and quantification of the differences in measured gamma-ray spectra from the application of Compton suppression. In the first configuration, several irradiated fuel elements of varying cooling times from the Penn State Breazeale Reactor spent fuel inventory were measured using the three collimated Compton suppression systems. In the second geometry, Compton suppressed measurements of two samples of Approved Test Material commercial fuel elements were recorded inside the guard detector annulus to simulate the siphoning of small quantities from the main process stream for long dwell measurement periods. Compton suppression was found to improve measured gamma-ray spectra of spent fuel for multivariate analysis by notably lowering the Compton continuum from dominant photopeaks such as 137Cs and 140La, due to scattered interactions in the detector, which allowed more spectral features to be resolved. There was a significant advantage demonstrated when measurements were recorded using the beam source configuration as opposed to the standard, enclosed Compton suppression system geometry.

환경 방사능 처리기술에서의 Compton suppression 및 Unsuppression system을 이용한 토양시료의 MDA 측정

환경 방사능 처리기술에서의 Compton suppression 및 Unsuppression system을 이용한 토양시료의 MDA 측정

Monte-Carlo optimisation of a Compton suppression system for use with a broad-energy HPGe detector

Monte-Carlo simulations are used to evaluate and optimise multiple components of a Compton Suppression System based upon a Broad-energy HPGe primary detector. Several materials for the secondary crystal are evaluated, including NaI(Tl), BGO and LaBr3(Ce). BGO was found to be the most effective across the required energy range, with the sizes of the proposed veto detector then optimised to extract the maximum performance for a given volume of material. Suppression factors are calculated for a range of nuclides (both single and cascade emitters) with improvements of 2 for the Compton Suppression Factors, and 10 for the continuum reduction when compared to the Compton suppression system currently in use. This equates to a reduction in the continuum by up to a factor of ~240 for radionuclides such as 60Co, which is crucial for the detection of low-energy, low-activity γ emitters typically swamped by such a continuum.

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.

Next Generation Detection Systems for Radioactive Material Analysis

Compton Suppression techniques have been widely used to reduce the Minimum Detectable Activity of various radionuclides when performing gamma spectroscopy of environmental samples. This is achieved by utilising multiple detectors to reduce the contribution of photons that Compton Scatter out the detector crystal, only partially depositing their energy. Photons that are Compton Scattered out of the primary detector are captured by a surrounding detector, and the corresponding events vetoed from the final dataset using coincidence based fast-timing electronics. The current work presents the use of a LynxTM data acquisition module from Canberra Industries (USA) to collect data in 'List-Mode', where each event is time stamped for offline analysis. A post-processor developed to analyse such datasets allows the optimisation of the coincidence delay, and then identifies and suppresses events within this time window. This is the same process used in conventional systems with fast-timing electronics, however, in the work presented, data can be re-analysed using multiple time and energy windows. All data is also preserved and recorded (in traditional systems, coincident events are lost as they are vetoed in real time), and the results are achieved with a greatly simplified experimental setup. Monte-Carlo simulations of Compton Suppression systems have been completed to support the optimisation work, and are also presented here.

Monte Carlo characterisation of a Compton suppressed broad-energy HPGe detector

GEANT4 Monte Carlo simulations have been successfully utilised to characterise a Compton suppressed broad-energy HPGe detector. The detector setup has been fully recreated in the simulation, which has been optimised to consistently reproduce the detector response. The peak efficiencies for both the primary BEGe detector and NaI(Tl) guard detectors agree with the simulated values for multiple test sources within 3 %. Compton suppression has also been simulated, with good agreement seen between the simulated and actual CSF values (<10 %) for multiple radionuclides. A secondary reference source was also simulated, which contained up to 30 radionuclides in a different geometry to that of the previous source. This showed excellent agreement with experimental data in both unsuppressed and suppressed modes of operation.

Performance of a total absorption clover detector for Qβ measurements of neutron-rich nuclei far from the β-stability line

To measure β-decay energies (Qβs) of neutron-rich nuclei far from the β-stability line, we have improved upon the previously described total absorption detector, composed of a clover Ge detector (80mmϕ×90mmL×4 crystals) and 4π BGO Compton suppressors. This detector can directly determine the Qβ from the end-point of the measured spectrum. Nuclei of interest such as new isotopes have Qβ values over 4MeV; therefore, high detection efficiencies are needed. This total absorption detector has a through-hole (alongside its vertical axis) at the center of the four Ge crystals, and the radioactive sources can be placed in this hole to measure the total absorption spectrum. The β- and γ-rays are absorbed by the detector with almost 4π geometry while escaping radiations from the Ge detector can be detected by the 4π BGO Compton suppressors. We also developed a practical analytic procedure based on the folding method, in which response functions of γ- and β-rays were considered with an assumed decay scheme. The systematic uncertainty of the deduced Qβs was evaluated to be ±30keV using 18 fission products whose Qβ values were precisely measured. With the detector and an on-line mass separator, we have determined the Qβ values of 166Eu and 165Gd for the first time, and have proposed more precise Qβ values for 160–165Eu and 163Gd than previously found. Owing to the especially good energy resolution of the detector, the isomeric state in 163Gd was also successfully observed for the first time through end-point analysis and analysis of the observed γ-rays. This result contributes to the determination of reliable Qβ values for 163Gd and 163Eu.

Performance evaluation of Compton suppression gamma spectrometer for low level environmental measurements

A Compton suppression gamma spectrometry system has been commissioned at Environmental Survey Laboratory and the results of performance evaluation are presented in the paper. The Compton suppression system is used to reduce the contribution of scattered gamma rays in the gamma spectrum that originate within the HPGe detector by an assembly of NaI (Tl) guard detectors surrounding the HPGe detector. The HPGe and NaI (Tl) are operated in anticoincidence mode to filter the Compton gamma rays emitting from the HPGe and subsequently resulting in the reduction of Compton continuum. The system was evaluated for various parameters such as energy calibration and efficiency calibration, resolution and Peak to Compton ratio (P/C). The Peak to Compton ratio with point sources of 137 Cs and 60 Co was found to be 1085:1 and 392:1 in Compton suppression mode compared to the normal mode operation of 142:1 and 66:1, respectively. The Minimum Detectable Activity of the system for various nuclides in Compton suppression mode as well as in normal mode of operations are also evaluated and discussed in the paper. The usability of suppression mode of counting for gamma emitters of cascade emissions is also discussed.