Escape Peak Research Articles

Carbon-based thin films as a suitable alternative to metallized films for the preparation of radioactive sources

A new method for radionuclide labeling by the use of graphene thin films was previously presented. In this work, a comparison among low energy radioactive sources supported on carbonaceous thin films on polyvinyl chloride-polyvinyl acetate copolymer (VYNS), based on the use of aqueous solutions is investigated as a feasible alternative to the traditional metallized films avoiding the downside of the loss of many broken films. Graphene-based materials were prepared by both oxidation-exfoliation-reduction and direct graphite exfoliation routes. In addition, multiwalled carbon nanotubes (MWCNTs) thin films were also evaluated. The stability of both carbonaceous materials aqueous dispersions were studied by using ionic and non-ionic surfactants. Solid carbon-based materials were characterized by X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) whereas the colloidal nature of the aqueous dispersions was verified by the measurement of Tyndall effect and the morphology of thin films was evaluated by Scanning Electron Microscopy (SEM). 55Fe solutions were used to prepare the radioactive sources on the thin films by quantitative drop deposition. The quality of spectra was measured in a pressurized proportional counter. Results showed a resolution higher than 0.9 keV for all the tested sources. However, MWCNT-based along with non-surfactant sources presented non-adequate escape peaks and low energy tails. On the contrary, all the graphene-based sources prepared using surfactants to stabilize aqueous solutions presented an energy resolution comparable to that of the metallized source while offering notable advantages in terms of cost efficiency and reliability of the as-prepared supports.

Virtual segmentation of a small contact HPGe detector: inference of hit positions of single-site events via pulse shape analysis

Exploring hit positions of recorded events can help to understand and suppress backgrounds in rare event searches. We propose a pulse shape analysis method to discriminate single-site events (SSEs) in the inner and outer layer of a small contact P-type germanium detector (HPGe). SSEs in the inner and outer layer have different pulse shape features, of which the rise time of the (TQ)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(T_{Q})$$\\end{document} and current pulse (TI)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(T_{I})$$\\end{document} are selected for discrimination. A 500 Bq Thorium-228 (Th-228) source is used to determine the boundaries between the two layers. The double escape peak events from 2614.5 keV γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}-ray are selected as typical SSEs, their numbers in the two layers are used to calculate the volumes and shapes of those layers. Considering the statistical and systematic uncertainties, the inner layer volume is evaluated to be 47.2% ± 0.26%(stat.) ± 0.18%(sys.) ± 0.22%(sys.) of the total sensitive volume. Selecting the inner layer as the analysis volume can reduce the external background in the signal region of Ge-76 neutrinoless double beta (0νββ)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ u \\beta \\beta )$$\\end{document} decay. We use the Th-228 data to validate the inner layer model and evaluate the background suppression power in the 0νββ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ u \\beta \\beta $$\\end{document} signal region (Qββ=2039\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(Q_{\\beta \\beta }=2039$$\\end{document} keV). The virtual segmentation further reduces the background from the external Th-228 source by about 10%. The virtual segmentation could be used to efficiently suppress surface background like electrons from Ar-42 decay in 0νββ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ u \\beta \\beta $$\\end{document} experiments using germanium detectors immersed in liquid argon.

Research on the minimum measurable mass of explosives hidden in concrete walls based on SVM and tagged neutron method

A method based on the combination of the tagged neutron method and the support vector machine (SVM) algorithm was proposed for the fast and effective identification of explosives behind concrete walls. Geant4 was used for modeling the experimental setup. The high degree of agreement in the experimental and simulated gamma spectra from selected time window validated the developed methodology. The difference between the experimental and simulated spectra could be inferred that the difference between the experimental and simulated spectra mainly comes from the difference in the composition of the cement. Geant4 was used for modeling the situation where explosives were hidden behind walls with thicknesses of 5 cm, 10 cm, and 15 cm, and the minimum detectable mass was calculated. The minimum detection limit (MDL) for C element in explosives hidden behind concrete walls is used to determine the minimum mass of explosives that can be detected and identified. The types of explosives hidden inside the wall were identified using SVM. The mass of explosives with 95% identification accuracy was considered to be the minimum measurable mass that can identify the type of explosives hidden within the wall. Cph/N and Cse/N were selected as input vectors to the SVM where Cph is the peak area of the inelastic scattering peak of element C, Cse is the peak area of the first escape peak of element C, and N is the peak area of the inelastic scattering peak of element N. Calculations of the minimum detectable mass of the type of explosive (TNT, AN, RDX) that could be effectively identified behind walls of 5, 10, and 15 cm resulted in 452 g, 539 g, and 893 g, respectively.

Cadmium Telluride (CdTe) Compound and Silicon (Si) Semiconductor Materials Detectors for X-Ray

There are different approaches and also materials to construct a detector for x-rays. the available semiconductor materials, Silicon (Si) is mainly used for charged particle detectors and soft X-ray detectors. Cadmium Telluride (CdTe) compound semiconductors for x-ray detectors have experienced a rather rapid development in the last few years, due to their appealing performance. In this paper we review the physical properties of semiconductor detectors for x-ray. In particular, we focus on compound semiconductor detectors. In addition, Si detector has better energy resolution achievement. However, it does not have good detection efficiency for higher energy above (40Kev). While CdTe detector supplies higher detection efficiency for x -rays about 100% for up to 100 keV in energy. The response functions of Si detector to reduce small x-ray, which has limited sensitivity for energy about 30keV. The XR-100T is high performance for x-ray and gamma ray detector by using 241Am (59.5keV), so the cooler are mounted the input FET a feedback components to the Amptek to charge sensitive preamplifier. Both the Si and CdTe detectors are connected to the PX2 combined amplifier and power supply, that was provide the voltage needed to operate XR-100T CdTe. The PX2 T CdTe amplifier has a Rise Time Discrimination circuit, measure the FWHM energy resolution of 55Fe (5.89) the peak in each spectrum hence a graph of energy resolution. Moreover, the Rise Time Discrimination So the escape peak of 55Fe was determined with Si detector was 11.66 keV, also k- sell x-ray energy was calculated to 5.77keV and the Rise Time Discrimination effect was studied on the spectrum when is it switched on and off. Its influence was found in decreasing the noise of the spectrum.

Electron non-linear light yield of LaBr[formula omitted] detector aboard GECAM

Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) is mainly designed to detect Gamma-Ray Bursts associated with gravitational wave events. The lanthanum bromide (LaBr3) scintillator with two types of doping (5% Ce3+ only, 5% Ce3+ co-doped with 1.5% Sr2+) are used in the Gamma-Ray Detectors (GRDs) of GECAM. Here, by analyzing the on-ground calibration data, we find different characteristics of these two doping types of LaBr3 scintillator, including the Energy-Channel (E-C) relation, photon non-proportional response, energy resolution, as well as the electron non-proportional response which is derived from photon response and Monte Carlo simulation with Bayesian inference method. The results also show that the photon scintillation light yield and energy resolution can be improved by co-doping Sr2+ in LaBr3:Ce3+ scintillator, owing to a direct inhibitory effect on the electron non-proportional response. By taking the electron non-proportional response into account, we find that the simulated spectrum is in good agreement with the measured one, including Compton structure, escape peak of Lanthanum and Bromine as well as full energy peak, indicating that the electron non-proportional response is an essential factor in the energy response of scintillator detector thus should be considered in the data analysis.

Pyrolysis characteristics, gas products, volatiles, and thermo–kinetics of industrial lignin via TG/DTG–FTIR/MS and in–situ Py–PI–TOF/MS

The lignosulfonates and de–alkalized lignin pyrolysis characteristics were evaluated by using TG/DTG–FTIR/MS and in–situ Py–PI–TOF/MS. TG/DTG experiments showed that lignin sample pyrolysis proceeded in three stages from 303.15 to 1173.15 K, and the thermographs shifted to higher temperatures with increasing heating rate. Gases MS analysis showed that the pyrolysis of sodium lignosulfonate produced more CH4 and CO2 than the pyrolysis products of calcium lignosulfonate and de–alkalized lignin. The escape temperature of volatile matter in the lignin samples were basically consistent with the order of its organic content, but there were obvious differences in product composition. The escape peak temperature of olefins, aromatics, monophenols, and bisphenols showed a decline trend with the increase of substituent carbon number. The sample pyrolysis thermo–kinetics was estimated by Coats–Redfern, FWO, KAS, and integral Master–plots methods. The activation energies were 66.74–678.20 kJ mol−1 (calcium lignosulfonate) > 32.24–598.38 kJ mol−1 (sodium lignosulfonate) > 44.27–265.69 kJ mol−1 (de–alkalized lignin). The most potential kinetic models were not all consistent with the standard curves for the stages of sample pyrolysis. This study provides theoretical and practical guidance for solving the engineering problems of lignin wastes pyrolysis in papermaking wastewater.

Variation in cosmic ray flux during Solar Eclipse on 21 June, 2020 at Jaipur, India

Variation in gamma ray flux was recorded during the Annular Solar Eclipse on 21 June, 2020 at Jaipur, India where 88.3% of the solar disk was eclipsed. Two Sodium Iodide NaI (Tl) scintillation detectors were employed for the experiment and flux was recorded in the energy range 300 keV to 2 MeV. The first detector employed to record data for the duration of 3 h and 30 min records a sizeable enhancement at the characteristic energy 1460 keV and the corresponding single escape peak at 949 keV. No substantial variation in the radiations was noticed by the detector employed for recording data for 20 critical minutes during the peak of the eclipse.

Boosting background suppression in the NEXT experiment through Richardson-Lucy deconvolution

Next-generation neutrinoless double beta decay experiments aim for half-life sensitivities of ∼ 1027 yr, requiring suppressing backgrounds to < 1 count/tonne/yr. For this, any extra background rejection handle, beyond excellent energy resolution and the use of extremely radiopure materials, is of utmost importance. The NEXT experiment exploits differences in the spatial ionization patterns of double beta decay and single-electron events to discriminate signal from background. While the former display two Bragg peak dense ionization regions at the opposite ends of the track, the latter typically have only one such feature. Thus, comparing the energies at the track extremes provides an additional rejection tool. The unique combination of the topology-based background discrimination and excellent energy resolution (1% FWHM at the Q-value of the decay) is the distinguishing feature of NEXT. Previous studies demonstrated a topological background rejection factor of ∼ 5 when reconstructing electron-positron pairs in the 208Tl 1.6 MeV double escape peak (with Compton events as background), recorded in the NEXT-White demonstrator at the Laboratorio Subterráneo de Canfranc, with 72% signal efficiency. This was recently improved through the use of a deep convolutional neural network to yield a background rejection factor of ∼ 10 with 65% signal efficiency. Here, we present a new reconstruction method, based on the Richardson-Lucy deconvolution algorithm, which allows reversing the blurring induced by electron diffusion and electroluminescence light production in the NEXT TPC. The new method yields highly refined 3D images of reconstructed events, and, as a result, significantly improves the topological background discrimination. When applied to real-data 1.6 MeV e−e+ pairs, it leads to a background rejection factor of 27 at 57% signal efficiency.

Differential cross section measurements of the 6.13 MeV gamma ray from proton-induced reaction of fluorine

Fundamental cross section measurements are essential for particle-induced gamma emission (PIGE) analysis. 19F(p,αγ2-0)16O can be utilized in PIGE analysis; however, differential cross section measurements for this reaction do not exist due to the difficulty in deconvolving overlapping peaks in the gamma spectrum. Although gamma yield measurements for this reaction exist (Dababneh et al., 1993), these can only be used for relative measurements. This work presents the 6.13 MeV gamma production differential cross sections for the 19F(p,αγ2-0)16O reaction in the incident proton kinetic energy range of 837 to 1517 keV. The yield of the 6.13 MeV gamma was obtained by subtracting the contribution of the 7.12 MeV double escape peak using the experimentally-determined ratio of the escape peaks. The corrected yields were converted to differential cross sections, which are presented here for the first time, as a contribution to the current knowledge and utilization of PIGE techniques.

Development of Gamma-Ray Position-Sensitive Transition-Edge-Sensor Microcalorimeters

Position-sensitive transition-edge sensor (TES) microcalorimeters (PoSTs) were developed to detect gamma rays up to a few MeV. Each gamma-ray PoST comprised a 0.5 mm × 0.5 mm × 19 mm lead absorber with a TES on each end and worked as a 1D imaging spectrometer. Only one TES worked at low temperature and its results are reported herein. We irradiated the PoST device with gamma rays from a Cs-137 source, and the resultant pulses showed strong correlations between the pulse height and the rise time. To determine effective pixels, we separately divided the photopeak and lead-K escape peak pulses into 19 groups after sorting them by their rise times. From the pulse shape distributions, we concluded that the TES was sensitive to the gamma-ray interaction position as long as it was not located too far away from the TES, and that it was probably possible to determine the interaction positions of the entire absorber, if both TESs were working. The PoST device was then modeled and the average pulses of the 19 effective pixels were compared to those of numerical simulations, where the rise time distributions of the actual pulses and simulated pulses were in good agreement.

Comprehensive characterization of ExacTrac stereoscopic image guidance system using Monte Carlo and Spektr simulations

The purpose of this work is to develop accurate computational methods to comprehensively characterize and model the clinical ExacTrac imaging system, which is used as an image guidance system for stereotactic treatment applications.The Spektr toolkit was utilized to simulate the spectral and imaging characterization of the system. Since Spektr only simulates the primary beam (ignoring scatter), a full model of ExacTrac was also developed in Monte Carlo (MC) to characterize the imaging system. To ensure proper performance of both simulation models, Spektr and MC data were compared to the measured spectral and half value layers (HVLs) values.To validate the simulation results, x-ray spectra of the ExacTrac system were measured for various tube potentials using a CdTe spectrometer with multiple added narrow collimators. The raw spectra were calibrated using a 57Co source and corrected for the escape peaks and detector efficiency. HVLs in mm of Al for various energies were measured using a calibrated RaySafe detector. Spektr and MC HVLs were calculated and compared to the measured values. The patient surface dose was calculated for different clinical imaging protocols from the measured air kerma and HVL values following the TG-61 methodology. The x-ray focal spot was measured by slanted edge technique using gafchromic films. ExacTrac imaging system beam profiles were simulated for various energies by MC simulation and the results were benchmarked by experimentally acquired beam profiles using gafchromic films. The effect of 6D IGRT treatment couch on beam hardening, dynamic range of the flat panel detector and scatter effect were determined using both Spektr simulation and experimental measurements.The measured and simulated spectra (of both MC and Spektr) for various kVps were compared and agreed within acceptable error. As another validation, the measured HVLs agreed with the Spektr and MC simulated HVLs on average within 1.0% for all kVps. The maximum and minimum patient surface doses were found to be 1.06 mGy for shoulder (high) and 0.051 mGy for cranial (low) imaging protocols, respectively. The MC simulated beam profiles were well matched with experimental results and replicated the penumbral slopes, the heel effect, and out-of-field regions. Dynamic range of detector (in terms of air kerma at detector surface) was found to be in the range of [6.1 × 10−6, 5.3 × 10−3] mGy.Accurate MC and Spektr models of the ExacTrac image guidance system were successfully developed and benchmarked via experimental validation. While patient surface dose for available imaging protocols were reported in this study, the established MC model may be used to obtain 3D imaging dose distribution for real patient geometries.

Using GEANT4 Monte Carlo simulations to resolve low energy [formula omitted]-ray spectra: The study of [formula omitted] decay using a broad energy HPGe detector

Within the present work a peak analysis and unfolding method for low energy γ-ray spectroscopy is presented. This method can be used to facilitate the determination of the peak integral of a photopeak, when Ge X-ray escape peaks contaminate the latter and in parallel the source activity and the emission rate of the recorded photons which produce the escape peaks are unknown. It is based on extensive Monte Carlo simulations of the spectra by taking the full advantage of power and accuracy provided by the GEANT4 simulation toolkit.

Obra-aula: processos, procedimentos e criação de uma artistagem docente

Este artigo versa sobre a contribuição que a arte contemporânea pode dar à docência. Objetiva-se evidenciar a possibilidade de uma Obra-Aula através da produção artística do pesquisador e como esta se relaciona com a artistagem (CORAZZA, 2013). Ao perceber os vazamentos que a arte contemporânea ocasiona à educação, mostra-se os encontros e experimentações com essas duas áreas. Delineia-se aqui um plano de consistência nas fronteiras borradas da filosofia, da arte e da educação. Nas Filosofias da Diferença de Gilles Deleuze e Félix Guattari (2010, 2011a, 2011b, 2015) encontra-se potência para manifestar as transformações dos significados hegemônicos incrustados nos significantes e nos signos. Partindo desse desenho monta-se um agenciamento, responsável por evidenciar os picos de fuga das relações estabelecidas. Procura-se referências de arte no fazer junto de Allan Kaprow (2003, 2004, 2010), nas sensações de Kazimir Malevich (GIL, 2010) e na zona invisível de Marcel Duchamp (PAZ, 2014), orientação para a prática artística do pesquisador na qual a representação de uma intenção em obra é rompida. O artigo se desenha em um método que se monta fazendo. Um passarinhar à moda de uma cartografia (DELEUZE; GUATTARI, 2011a) que voa por um território encontrando forças passarinhar. Pousando sobre os artistas referência e bicando frutos poéticos, ele canta uma Obra-Aula que faz melodia com a artistagem docente (CORAZZA, 2012). Uma maneira de justapor elementos variados para pensar o impensado, bem como flautear o inflauteável.

Modeling of the response function of CdTe detectors for a hard X-ray synthetic diagnostic

Abstract The response function of CdTe detectors used in a hard X-ray spectrometer system (HXRS) on the TCV tokamak fusion experiment is modeled based on the measured energy spectra from multiple gamma-ray sources. The response function consists of an asymmetric Gaussian photopeak, an exponentially inclined shelf structure below the photopeak, and CdTe escape peaks. It is demonstrated that the measured energy spectra of radioactive sources can be correctly reconstructed using this response function. This model is applied to a hard X-ray synthetic diagnostic used to convert a modeled electron distribution function to a measured hard X-ray signal, for the study of energetic electrons in the TCV tokamak.

Active interrogation of Special Nuclear Material containers using AmBe quasi-forward biased directional source and PGNAA

Special Nuclear Material (SNM) including 95% 235U and 239Pu is capable of being identified by utilizing a quasi-forward directional AmBe source from Patent No: US20190013109A1 using Prompt Gamma Neutron Activation Analysis (PGNAA) simulated with Monte-Carlo N-Particle transport 6.2 (MCNP). HPGe and LaBr3 detector arrays were used to identify and quantify the peak-to-background and peak-to-total ratios of the associated photon spectra from the SNM encased in a polyethylene shield. The conducted simulations varied the volume of the SNM and neutron source strength in the MCNP data card to conduct an uncertainty analysis. Photopeaks identified include K-shell X-rays from 235U and 239Pu, 61 keV from fission, 2.223 MeV prompt gamma from hydrogen, 511 keV annihilation, and a single and double escape peak from the prompt gamma interaction from hydrogen. Relationships between peak-to-total and peak-to-background as a function of SNM and particle history were investigated to aid in the analysis. The capabilities of both detector systems to acquire well resolved photopeak with a 5% relative error or less, with a 1 Ci source activity, and a peak-to-background ratio of 1.15. This was determined to take 326 s for LaBr3 and 163 s for HPGe which is comparable to current methods for material detection which take between 100 and 900 s to acquire.

The Influence of Spectral Interferences on Critical Element Determination with Portable X-Ray Fluorescence (pXRF)

Field portable X-ray fluorescence (pXRF) spectrometers are routinely used in mineral resources studies. To date, mineral resources studies have largely focussed on the application of pXRF to the exploration for deposits of base and precious metals. By contrast, studies using pXRF for the quantification of critical elements in geological materials are scarce since these elements are difficult to determine with energy-dispersive pXRF technology. This study explores the capability of pXRF spectrometers to detect and quantify critical elements (Ba, P, Nb, V, Co, REE, W, Bi, Hf, and Ta) in certified reference materials (CRMs). While precision of many critical elements is acceptable (&lt;20% RSD), accuracy can be poor (&gt;50% difference) when using pre-installed factory calibration software. Spectra collected during the pXRF measurements show that poor accuracy and false positives tend to be associated with spectral interferences. Distinct combinations of spectral interferences (line overlaps, Compton scattered peaks, and Si escape peaks) were observed in the different matrix types. Our results show that critical elements may be determined in common geological materials when pronounced peaks occur in the spectra and that matrix-match of standards and samples is essential. Hence, XRF spectra should be routinely reviewed to identify erroneous quantification due to spectral interferences.

Precision imaging of 4.4 MeV gamma rays using a 3-D position sensitive Compton camera

Imaging of nuclear gamma-ray lines in the 1–10 MeV range is far from being established in both medical and physical applications. In proton therapy, 4.4 MeV gamma rays are emitted from the excited nucleus of either 12C* or 11B* and are considered good indicators of dose delivery and/or range verification. Further, in gamma-ray astronomy, 4.4 MeV gamma rays are produced by cosmic ray interactions in the interstellar medium, and can thus be used to probe nucleothynthesis in the universe. In this paper, we present a high-precision image of 4.4 MeV gamma rays taken by newly developed 3-D position sensitive Compton camera (3D-PSCC). To mimic the situation in proton therapy, we first irradiated water, PMMA and Ca(OH)2 with a 70 MeV proton beam, then we identified various nuclear lines with the HPGe detector. The 4.4 MeV gamma rays constitute a broad peak, including single and double escape peaks. Thus, by setting an energy window of 3D-PSCC from 3 to 5 MeV, we show that a gamma ray image sharply concentrates near the Bragg peak, as expected from the minimum energy threshold and sharp peak profile in the cross section of 12C(p,p)12C*.

Improving sensitivity of a BEGe-based high-purity germanium spectrometer through pulse shape analysis

We performed Pulse Shape Analysis to separate single-scattered gamma energy deposition events from multiple-scattered photons in a high-sensitivity gamma -ray spectrometer. The spectrometer is based on a Broad Energy High Purity Germanium detector and the developed technique uses multivariate analysis by an application of the Multi-Layer Perceptron Neural Network. A very good separation of the single-site- and multi-site events was achieved leading to a significant reduction of the background level of the investigated spectrometer – the double escape peak, rich in single-site events, was reduced by 95%, while the full energy peaks lost at most 25% of their counts. The peak to Compton ratio, calculated for the 2614.5 keV gamma line from ^{208}Tl, was improved by 114.3%.

Gamma spectrum and coincidence summation simulations with Geant4 in the analysis of radionuclide using BEGe detector

A Geant4 application has been developed to simulate the gamma spectrum of a BEGe detector. The summation effects were encompassed for both random and true coincidences through a time-based approach. The application well reproduces the typical spectral features such as full energy peaks, escape peaks, summation peaks and Compton/backscatter continuum. The simulated gamma response is consistent with empirical data within 3%, while simulations of the X-ray and baseline regions are valid within a 10% deviation.

CeBr3 scintillators for 4He prompt gamma spectroscopy: Results from a Monte Carlo optimization study

Range uncertainties limit the potential of charged particle therapy. In vivo and online range verification techniques could increase the confidence in the dose delivery distribution and lead to more conformal treatments. Prompt gamma imaging and prompt gamma spectroscopy (PGS) have been demonstrated for such a purpose. The successful application of these techniques requires the development of a dedicated detector system optimized to the radiation energy ranges and the intensity. In this work, we investigated a detector system based on CeBr3 crystals capable of performing spectroscopy of the prompt gamma radiation induced by 4 He beams. We performed Monte Carlo simulations to optimize the detector system. The study was carried out both with the Geant4 toolkit and the FLUKA package. The simulated system consisted of a primary crystal for spectroscopy and secondary crystals for noise reduction in anticoincidence (AC). For comparison purposes, we considered a configuration without AC crystals. We first defined the dimensions of the primary cerium bromide (CeBr3 ) crystal and the secondary bismuth germanate (BGO) or CeBr3 crystals. We then evaluated their detection performance for monoenergetic gamma radiation up to 7MeV in such way that the probability of the photo-peak detection was maximized in comparison to the number of escape peak and Compton events. We simulated realistic prompt gamma radiation spectra induced by 4 He beams on homogeneous targets (water, graphite, and aluminum) and on implants (water with an aluminum insert). Finally, we tested the performances of the optimized systems in the detection of the realistic gamma spectra. The quantitative analysis was accomplished by comparing the signal-to-noise ratio between the different configurations and the ability to resolve the discrete reactions. We present the optimized dimensions for the primary CeBr3 crystals with and without AC shielding. The specific values are given over a wide range of crystal volumes. The results show an optimal primary CeBr3 crystal with an approximately diameter to length ratio of 1 without AC shielding and 0.5 with AC shielding. The secondary BGO and CeBr3 should have a transverse dimension of 3 and 4.56cm, respectively. The analysis of the prompt gamma spectra from 4 He beams highlighted the presence of specific discrete reactions not observed in 1 H studies, for example, 12 C transition 0+ (7.65MeV) →2+ (4.44MeV). This reaction is responsible for the generation of the 3.21MeV prompt gamma peak. The optimized primary crystal provides a significant increase in the signal-to-noise ratio together with an improved resolution of the discrete gamma lines, especially in the high-energy region. The detection configuration with an optimized anticoincidence crystal improved the signal-to-noise ratio up to a factor of 3.5. This work provides the optimal geometry for primary and secondary crystals to be used in range verification through PGS. The simulations show that such a PGS system may allow for the simultaneous detection of the discrete lines from a thin metal implant within a water phantom.