Prompt Gamma Research Articles

Chemical analyses on late antique glass finds from Histria, Romania

AbstractThis paper reports the chemical composition of 36 glass finds from Histria, Romania, mainly dated to the Late Antique period (4th–6th c. AD) obtained by Prompt Gamma Activation Analysis (PGAA) at the Budapest Neutron Centre (BNC). Histria glass fragments were identified as Série 2.1, Série 3.2, and Série 3.3 of Foy, HIMT, Roman, and Sb decolorized. Most of the analyzed objects were manufactured from glass originating in Egyptian primary workshops. These analytical results are an additional proof for the trade connection of Histria with the rest of the Roman Empire.

Feasibility of Prompt Gamma Ray Detection and Imaging Using CdTe Detectors for BNCT ― Monte Carlo Study

Boron neutron capture therapy (BNCT) has experienced a renaissance in recent years, due to the availability of accelerator-based neutron sources and more effective delivery vehicles of boron-10 (10B). For successful BNCT, 10B concentration and distribution in the tumor (as well as in the critical organs) must be determined non-invasively prior to BNCT treatments. While conventional nuclear imaging (e.g., PET/SPECT), in conjunction with radiolabeled 10B, may serve for this purpose, another approach, based on the detection of prompt gamma (PG) rays from the BNC reaction, appears to be more attractive, most notably because it can be implemented within the BNCT setup without radiolabeling of 10B. The detectability of PG rays (478 keV) from the BNC reaction has been shown experimentally within the context of BNCT utilizing energy-resolving solid-state detectors. However, the feasibility of this approach under the clinically relevant conditions is currently unknown. Thus, the present work investigated this feasibility by performing Monte Carlo (MC) simulations using the simulation toolkit.MC models of various phantom cases were created to simulate epithermal neutron beam irradiation relevant to accelerator-based BNCT (a-BNCT). For benchmarking and future experimental verification, the phantom geometry (20 cm-diameter/24 cm-height cylinder) and material (PMMA) were chosen based on a published experimental study. The phantom had 3 cm-diameter/3.8 cm-height cylindrical inserts (located at 5 cm depth along the long-axis of the phantom) that contained 10B solution at different concentrations ranging from 1 - 30,000 parts-per-million (ppm). For detection of PG rays, a 23.1 cm-diameter ring detector consisting of 120 cadmium telluride (CdTe) crystals was modeled. CdTe was chosen because of its high photon counting efficiency and energy resolution. Each CdTe detector crystal (5 × 5 × 1 mm3) contained an inherent 0.1mm-thick beryllium window and a novel/custom thermal neutron filter made of gadolinium. Two billion incident neutron histories were used during each MC simulation. The detected PG ray signals were used to test both direct mapping and CT techniques for quantitative imaging.The current MC simulations showed PG ray signals from the10B-loaded tumor-mimicking cylindrical insert were above the background noise (with a 95% confidence level), down to the clinically achievable tumor 10B concentration of 30 ppm. The custom thermal neutron filter was effective in suppressing the inherent background from CdTe detectors.This MC study demonstrated the detectability of PG rays from the BNC reaction using CdTe detectors under the conditions closely mimicking realistic a-BNCT scenarios. It also showed that clinically acceptable quantitative imaging of 10B distribution could be performed utilizing the PG ray signals from the BNC reaction.H. Moktan: None. C. Lee: None. S. Cho: Research Grant; TAE Life Sciences.

Upgrade of gamma electron vertex imaging system for high-performance range verification in pencil beam scanning proton therapy

In proton therapy, a highly conformal proton dose can be delivered to the tumor by means of the steep distal dose penumbra at the end of the beam range. The proton beam range, however, is highly sensitive to range uncertainty, which makes accurately locating the proton range in the patient difficult. In-vivo range verification is a method to manage range uncertainty, one of the promising techniques being prompt gamma imaging (PGI). In earlier studies, we proposed gamma electron vertex imaging (GEVI), and constructed a proof-of-principle system. The system successfully demonstrated the GEVI imaging principle for therapeutic proton pencil beams without scanning, but showed some limitations under clinical conditions, particularly for pencil beam scanning proton therapy. In the present study, we upgraded the GEVI system in several aspects and tested the performance improvements such as for range-shift verification in the context of line scanning proton treatment. Specifically, the system showed better performance in obtaining accurate prompt gamma (PG) distributions in the clinical environment. Furthermore, high shift-detection sensitivity and accuracy were shown under various range-shift conditions using line scanning proton beams.

Improvement of Neutron Safety Performance of Devices Used in the Prompt Gamma Activation Analysis Technique (PGAA) in Morocco: Modeling and Simulation

Improvement of Neutron Safety Performance of Devices Used in the Prompt Gamma Activation Analysis Technique (PGAA) in Morocco: Modeling and Simulation

Performance of CVD diamond detectors for single ion beam-tagging applications in hadrontherapy monitoring

In the context of online ion range verification in particle therapy, the CLaRyS collaboration is developing Prompt-Gamma (PG) detection systems. The originality in the CLaRyS approach is to use a beam-tagging hodoscope in coincidence with the gamma detectors to provide both temporal and spatial information of the incoming ions. The ion range sensitivity of such PG detection systems could be improved by detecting single ions with a 100ps (σ) time resolution, through a quality assurance procedure at low beam intensity at the beginning of the treatment session. This work presents the investigations that led to assessment of the Chemical Vapor Deposition (CVD) diamond detectors performance to fulfill these requirements. A 90Sr beta source, 68MeV protons, 95 MeV/u carbon ions and a synchrotron X-ray pulsed beam were used to measure the time resolution, single ion detection efficiency and proton counting capability of various CVD diamond samples. An offline technique, based on double-sided readout with fast current preamplifiers used to improve the signal-to-noise ratio, is also presented. The different tests highlighted Time-Of-Flight resolutions ranging from 13ps (σ) to 250ps (σ), depending on the diamond crystal quality and the particle type and energy. The single 68MeV proton detection efficiency of various large area polycrystalline (pCVD) samples was measured to be >96% using coincidence measurements with a single-crystal reference detector. Single-crystal CVD (sCVD) diamond proved to be able to count a discrete number of simultaneous protons while it was not achievable with a polycrystalline sample. Considering the results of the present study, two diamond hodoscope demonstrators are under development: one based on sCVD, and one of larger size based on pCVD. They will be used for the purpose of single ion as well as ion bunches detection, either at reduced or clinical beam intensities.

Obsidian in the Early Neolithic of the Upper Vistula basin: origin, processing, distribution and use – a case study from Tominy (southern Poland)

Abstract The inflow of the Carpathian obsidian into the areas on the northern side of the Carpathians and the Sudetes is confirmed as early as in the Palaeolithic. However, its greatest intensity occurred in the Early Neolithic, i. e. in the late 6th and in the first half of 5th millennia BC. During that period, the phenomenon was closely related with the development of the Danubian cultural groups in the upper Vistula river basin, including especially Linear Pottery culture (LBK) and Malice Culture. The constant presence of this raw material products in mentioned areas is documented from the classical (musical-note) phase of LBK, constituting one of the most expressive pieces of evidence of permanent and intense intercultural contacts with communities of the northern Carpathian Basin. This phenomenon has been repeatedly emphasized in the literature. One of the most numerous LBK obsidian inventories in the upper Vistula river basin was obtained at site 6 in Tominy, located in southern Poland, in the non-loess zone of the Sandomierz Upland northern foreground. The above-mentioned collection, its non-destructive elemental analysis, using Prompt Gamma Activation Analysis (PGAA) and also traceological analysis, is the subject of this article. The results supplement the published data to a significant extent, simultaneously providing partial verification and updating of the current state of knowledge on the basic issues related to the Early Neolithic obsidian inflow into areas located North of the Carpathians, including primarily the origin of the raw material, the scale of its processing and distribution ways, as well as the range of its use by the LBK communities.

Monte Carlo evaluation of a LYSO-based Compton camera using two origin ensemble algorithms with resolution recovery.

Due to the lack of depth-of-interaction information, a Compton camera made of lutetium-yttrium orthosilicate (LYSO) crystals suffers from poor spatial resolution, which may lead to an unreliable range verification in proton therapy. The aim of this study is to evaluate the performance of a LYSO-based Compton camera using the origin ensemble algorithm with resolution recovery (OE-RR). We also proposed a regularized version of OE-RR called ROE-RR. We simulated a two-layer LYSO-based Compton camera which was used to detect prompt gammas (PGs) produced by a proton beam irradiated on a water phantom. PG images reconstructed by the OE-RR algorithm were evaluated and compared with those reconstructed by the proposed ROE-RR algorithm. Our simulated results show that both the OE-RR and ROE-RR algorithms could provide an accurate estimate of the Bragg peak position, with a mean positioning error of 2.5mm. Compared to the OE-RR algorithm, the proposed ROE-RR algorithm is less sensitive with respect to initial conditions and requires less iterations for converging to equilibrium. More importantly, the proposed ROE-RR algorithm could provide better image quality than the OE-RR algorithm, especially in low-count data. For LYSO-based Compton cameras, using a resolution-recovery image reconstruction algorithm is essential for reliable range verification.

First-In-Human Validation of CT-Based Proton Range Prediction Using Prompt Gamma Imaging in Prostate Cancer Treatments

Uncertainty in computed tomography (CT)-based range prediction substantially impairs the accuracy of proton therapy. Direct determination of the stopping-power ratio (SPR) from dual-energy CT (DECT) has been proposed (DirectSPR), and initial validation studies in phantoms and biological tissues have proven a high accuracy. However, a thorough validation of range prediction in patients has not yet been achieved by any means. Here, we present the first systematic validation of CT-based proton range prediction in patients using prompt gamma imaging (PGI). A PGI slit camera system with improved positioning accuracy, using a floor-based docking station, was used. Its overall uncertainty for range prediction validation was determined experimentally with both x-ray and beam measurements. The accuracy of range prediction in patients was determined from clinical PGI measurements during hypofractionated treatment of 5 patients with prostate cancer - in total 30 fractions with in-room control-CTs. For each pencil-beam-scanning spot, the range shift was obtained by comparing the PGI measurement to a control-CT-based PGI simulation. Three different SPR prediction approaches were applied in simulations: a standard CT-number-to-SPR conversion (Hounsfield look-up table [HLUT]), an adapted HLUT (DECT optimized), andDirectSPR. The spot-wise weighted mean range shift from all spots served as a measure for the accuracy of the respective range prediction approach. A mean range prediction accuracy of 0.0% ± 0.5%, 0.3% ± 0.4%, and 1.8% ± 0.4% was obtained for DirectSPR, adapted HLUT, and standard HLUT, respectively. The overall validation uncertainty of the second-generation PGI slit camera is about 1mm (2σ) for all approaches, which is smaller than the range prediction uncertainty for deep-seated tumors. For the first time, range prediction accuracy was assessed in clinical routine using PGI range verification in prostate cancer treatments. Both DECT-derived range prediction approaches agree well with the measured proton range from PGI verification, whereas the standard HLUT approach differs relevantly. These results endorse the recent reduction of clinical safety margins in DirectSPR-based treatment planning in our institution.

A time-of-flight-based reconstruction for real-time prompt-gamma imaging in proton therapy

We propose a novel prompt-gamma (PG) imaging modality for real-time monitoring in proton therapy: PG time imaging (PGTI). By measuring the time-of-flight (TOF) between a beam monitor and a PG detector, our goal is to reconstruct the PG vertex distribution in 3D. In this paper, a dedicated, non-iterative reconstruction strategy is proposed (PGTI reconstruction). Here, it was resolved under a 1D approximation to measure a proton range shift along the beam direction. In order to show the potential of PGTI in the transverse plane, a second method, based on the calculation of the centre of gravity (COG) of the TIARA pixel detectors’ counts was also explored. The feasibility of PGTI was evaluated in two different scenarios. Under the assumption of a 100 ps (rms) time resolution (achievable in single proton regime), MC simulations showed that a millimetric proton range shift is detectable at 2σ with 108 incident protons in simplified simulation settings. With the same proton statistics, a potential 2 mm sensitivity (at 2σ with 108 incident protons) to beam displacements in the transverse plane was found using the COG method. This level of precision would allow to act in real-time if the treatment does not conform to the treatment plan. A worst case scenario of a 1 ns (rms) TOF resolution was also considered to demonstrate that a degraded timing information can be compensated by increasing the acquisition statistics: in this case, a 2 mm range shift would be detectable at 2σ with 109 incident protons. By showing the feasibility of a time-based algorithm for the reconstruction of the PG vertex distribution for a simplified anatomy, this work poses a theoretical basis for the future development of a PG imaging detector based on the measurement of particle TOF.

GaN-Based Readout Circuit System for Reliable Prompt Gamma Imaging in Proton Therapy

Prompt gamma imaging is one of the emerging techniques used in proton therapy for in-vivo range verification. Prompt gamma signals are generated during therapy due to the nuclear interaction between beam particles and nuclei of the tissue that is detected and processed in order to obtain the position and energy of the event so that the benefits of Bragg’s peak can be fully utilized. This work aims to develop a gallium nitride (GaN)-based readout system for position-sensitive detectors. An operational amplifier is the module most used in such a system to process the detector signal, and a GaN-based operational amplifier (OPA) is designed and simulated in LTSpice. The designed circuit had an open-loop gain of 70 dB and a unity gain frequency of 34 MHz. The slew rate of OPA was 20 V/μs and common mode rejection ratio was 84.2 dB. A simulation model of the readout circuit system using the GaN-based operational amplifier was also designed, and the result showed that the system can successfully process the prompt gamma signals. Due to the radiation hardness of GaN devices, the readout circuit system is expected to be more reliable than its silicon counterpart.

Characterization of (252Cf-ZrH2) Monte Carlo model for detection of nitrogen and chlorine by thermal neutron-capture PGNAA

Monte Carlo calculations were conducted to explore the potentials of zirconium hydride (ZrH2) as possible alternative moderator for high density polyethylene (HDPE) and water (H2O) in a simple (100MBq) 252Cf-based Prompt Gamma Neutron Activation Analysis (PGNAA) assembly. The thickness of moderators was optimized against thermal neutron flux (ϕth) as well as the ratio of (thermal/fast) neutron flux (ϕth/ϕfast), calculated at the sample cavity. The capabilities of moderating 252Cf source neutrons and minimizing the γ-background due to 2525Cf fission γ-rays, 1H(nth,γ)2H γ-rays originates in the moderator as well as other (nth,γ) capture reactions from surroundings were investigated. The optimal selected moderator with sufficient (ϕth) at the sample cavity and minimum γ-contamination was selected as ZrH2 for use in a252Cf-PGNAA for detection of nitrogen and chlorine in bulk sample simulants of melamine (C3H6N6) and sodium chloride (NaCl). The prompt γ-rays spectra were analyzed to detect the 10.83 MeV and 6.11 MeV prompt γ-peaks released by 14N(nth,γ)15N and 35Cl(nth,γ)36Cl, respectively. The results showed that the (252Cf-ZrH2)-PGNAA model has positively identified nitrogen with net counts (1.25 × 105 n.cm−2.s−1) and Chlorine with net counts of (4.19 × 106 n.cm−2.s−1), achieving minimum detectable concentrations of about (350 ppm at 10.83 MeV) and (640 ppm at 6.11 MeV), respectively.

Neutron guide optimization for the Moroccan PGAA system

The Moroccan TRIGA Mark II research reactor is to be equipped with a PGAA (Prompt Gamma Activation Analysis) facility to assist the country's progression in socioeconomic areas such as the environment and geochemistry, agriculture, health, industry, cultural heritage, and human sciences. The requirements of the PGAA facility include a very high thermal to fast neutron flux ratio and a focused, thin beam. Supermirror neutron guides are generally used to meet such requirements due to their ability to reflect neutrons with a specific energy and scattering angle. This study was undertaken to determine a suitable neutron guide for achieving optimal performance for the PGAA facility, where such a determination needs to be made according to both the available space and the minimum performance needed for PGAA analysis. To better parameterize the neutron guide, a set of simulations were performed with the aim of establishing the best guide specifications. Three types of neutron guides were studied, namely straight, curved, and bender. McStas code was used in this study, and the simulations showed that the guides must be 6 m long and that the coating value m must be equal to 5 for the bender and straight guides and 6 for the curved guide. Among the three guide types, the thermal/epithermal (Фth/Фep) and thermal/fast (Фth/Фfast) ratios were found to be much better when using the curved guide.

Secondary Particle Interactions in a Compton Camera Designed for in vivo Range Verification of Proton Therapy.

The purpose of this study was to determine the types, proportions, and energies of secondary particle interactions in a Compton camera (CC) during the delivery of clinical proton beams. The delivery of clinical proton pencil beams ranging from 70 to 200 MeV incident on a water phantom was simulated using Geant4 software (version 10.4). The simulation included a CC similar to the configuration of a Polaris J3 CC designed to image prompt gammas (PGs) emitted during proton beam irradiation for the purpose of in vivo range verification. The interaction positions and energies of secondary particles in each CC detector module were scored. For a 150-MeV proton beam, a total of 156,688(575) secondary particles per 108 protons, primarily composed of gamma rays (46.31%), neutrons (41.37%), and electrons (8.88%), were found to reach the camera modules, and 79.37% of these particles interacted with the modules. Strategies for using CCs for proton range verification should include methods of reducing the large neutron backgrounds and low-energy non-PG radiation. The proportions of interaction types by module from this study may provide information useful for background suppression.

Experimental determination and simulation of neutron and gamma flux parameters in horizontal channel for Prompt Gamma Neutron activation analysis implementation at Es-Salam research reactor

Since 2004, the k0-standardization method has been applied and evaluated in three experimental channels at Es-Salam research reactor of the Algerian Centre de Recherche Nucléaire de Birine (CRNB). The NAA laboratory at CRNB is well involved in the implementation of the Prompt Gamma Neutron Activation Analysis to extend the field of analyses to some additional elements to the NAA method. In the frame work of the PGNAA research project, several works have been carried out in the present study including the experimental and simulation characterization of neutron and gamma flux parameters of the horizontal channel. The absolute and relative neutron fluxes of the studied channel have been determined by using a set of monitors including Al, Au, Cu, Fe and Zr. Furthermore, measurements of gamma and thermal neutron doses have been achieved using LiF: Mg, Ti (TLD 600 and TLD 700) detectors. The gamma dose rate at the experimental channel center position was found to be 0.6 Gy/min·MW. The experimental results obtained in this study have been used as input information for simulations and design of neutron facilities and radiation shielding, which are successfully established by SCALE code. The results were compared in terms of spectral detail and precision and a good agreement has been revealed. The value of the thermal neutron flux was found to be (6.29 ± 0.25) E+08 n/cm2.s which allows the implementation of PGNAA at the Es-Salam research reactor.

Kilogram Sample Analysis by Nuclear Analytical Techniques: Complementary Opportunities for the Mineral and Geosciences

Sample-size reduction including homogenization is often required to obtain a test portion for element compositional analysis. Analyses of replicate test portions may provide insight into the sampling constant, and often much larger quantities are needed to limit the contribution of sampling error. In addition, it cannot be demonstrated that the finally obtained test portion is truly representative of the originally collected material. Nuclear analytical techniques such as neutron and photon activation analysis and (neutron-induced) prompt gamma activation analyses can now be used to study and overcome these analytical problems. These techniques are capable of obtaining multi-element measurements from irregularly shaped objects with masses ranging from multiple grams to multiple kilograms. Prompt gamma analysis can be combined with neutron tomography, resulting in position-sensitive information. The analysis of large samples provides unprecedented complementary opportunities for the mineral and geosciences. It enables the experimental assessment of the representativeness of test portions of the originally collected material, as well as the analysis of samples that are not allowed to be sub-sampled or dissolved, the analysis of materials that are difficult to be homogenized at large, and studies on the location of inhomogeneities. Examples of such applications of large-sample analyses are described herein.

Accounting for prompt gamma emission and detection for range verification in proton therapy treatment planning

Prompt gamma (PG) imaging is widely investigated as one of the most promising methods for proton range verification in proton therapy. The performance of this technique is affected by several factors like tissue heterogeneity, number of protons in the considered pencil beam and the detection device. Our previous work proposed a new treatment planning concept which boosts the number of protons of a few PG monitoring-friendly pencil beams (PBs), selected on the basis of two proposed indicators quantifying the conformity between the dose and PG at the emission level, above the desired detectability threshold. To further explore this method at the detection level, in this work we investigated the response of a knife-edge slit PG camera which was deployed in the first clinical application of PG to proton therapy monitoring. The REGistration Graphical User Interface (REGGUI) is employed to simulate the PG emission, PG detection as well as the corresponding dose distribution. As the PG signal detected by this kind of PG camera is sensitive to the relative position of the camera and PG signal falloff, we optimized our PB selection method for this camera by introducing a new camera position indicator identifying whether the expected falloff of the PG signal is centered in the field of view of the camera or not. Our camera-adapted PB selection method is investigated using computed tomography (CT) scans at two different treatment time points of a head and neck, and a prostate cancer patient under scenarios considering different statistics level. The results show that a precision of 0.8 mm for PG falloff identification can be achieved when a PB has more than 2 × 108 primary protons. Except for one case due to unpredictable and comparably large anatomical changes, the PG signals of most of the PBs recommended by all our indicators are observed to be reliable for proton range verification with deviations between the inter-fractional shift of proton range (as deduced from the PB dose distribution) and the detected PG signal within 2.0 mm. In contrast, a shift difference up to 9.6 mm has been observed for the rejected PBs. The magnitude of the proton range shift due to the inter-fractional anatomical changes is observed to be up to 23 mm. The proposed indicators are shown to be valuable for identifying and recommending reliable PBs to create new PG monitoring-friendly TPs. Comparison between our PB boosting method and the alternative PB aggregation, which combines the signal of nearby PBs to reach the desired counting statistics, is also discussed.

Measuring prompt gamma-ray emissions from elements found in tissue during passive-beam proton therapy

Prompt gamma detection during proton radiotherapy for range verification purposes will need to operate in both active and passive treatment beam environments. This paper describes prompt gamma measurements using a high resolution 2″ × 2″ LaBr3 detector for a 200 MeV clinical passive-scatter proton beam. These measurements examine the most likely discrete prompt gamma rays emitted from tissue by detecting gammas produced in water, Perspex, carbon and liquid-nitrogen targets. Measurements were carried out at several positions around the depth corresponding to the location of the Bragg peak for water and Perspex targets in order to investigate prompt gamma emission as a function of depth along the beam path. This work also focused on validating the Geant4 Monte Carlo model of the passive-scatter proton beam line and LaBr3 detector by making a direct comparison between the simulated and experimental results. The initial prompt gamma measurements were overwhelmed by the high amount of scattered radiation when measuring at isocenter, shifting the target further downstream from the final collimator significantly reduced the background radiation. Prompt gamma peaks were then clearly identified for the water, Perspex and graphite targets. The developed Geant4 Monte Carlo model was able to replicate the measured prompt gamma ray energy spectra, including production for important photopeaks to within 10%, except for the 4.44 MeV peak from the water target, which had more than a 50% overestimation of the number of produced prompt gamma rays. The prompt gamma measurements at various depths correlated well with the proton dose deposition; the 4.44 and 6.13 MeV photopeak profiles peaked within 1 cm of the Bragg peak and the R50% value for the 3–7 MeV energy range predicted the proton range within 8 mm.

Neutron beam characterization for the Moroccan TRIGA Mark II reactor

The TRIGA Mark II research reactor is equipped with four horizontal beam tubes and one thermal column. The tangential (NB1) and Percy (NB2) beam tube, which are the subject of this study, are dedicated to Prompt Gamma Neutron Activation Analysis and Neutron Imaging, and (Neutron Diffraction) facilities, respectively. A preliminary neutron characterization is needed for each beam tube. Basic beam parameters, including neutron flux, were measured with threshold activation detectors for the two beam tubes (NB1, NB2). Activity measurement through gamma spectrometry was performed with a high-purity germanium detector to evaluate the neutron flux through multiple analyses of activation detectors. The results were compared with those obtained using an approximated Monte Carlo simulation model for the reactor. A comparison between the experimental and simulated results revealed a good level of agreement.

Characterization of Neutron and Gamma Beams at the Tangential Beam Port of TRIGA 2000 Reactor Using Monte Carlo Methods

Characterization neutron and gamma beams at the tangential beam port of TRIGA 2000 reactor was done in order to prepare the development of Prompt Gamma Neutron Activation Analysis (PGNAA) facility. Characterization was performed by simulation using Monte Carlo method with MCNPX and PHITS computer codes. The MCNPX code was used to simulate the neutron-gamma fluence and energy spectra in the reactor core from fission reactions. The PHITS code was used to simulate the distribution of the neutron-gamma fluence and energy spectra in the tangential beam port. The simulation was done by modeling the geometry and elemental composition of reactor material and radiation source model in the form of fission reaction in the reactor core. The results indicate that the tangential beam port provides better neutron spectrum and neutron-gamma fluence ratio for PGNAA. These results will be used to simulate the colimator design and neutron interaction with samples in PGNAA facility.

Modeling and simulating the induced effect on the steel collimator plug used in the PGAA facility of the Moroccan TRIGA Mark-II reactor under different neutron irradiation levels

The main objective of this study is to assess the behavior of the steel collimator plug (steel plug) dedicated to the Prompt Gamma Neutron Activation Analysis (PGAA) facility in the neutron beam tube (NB1) of the 2 MW Moroccan TRIGA Mark-II research reactor. The main function of this steel plug is to reduce the neutron and gamma beam cross section from 15 cm to 5 cm in diameter. This steel plug plays a crucial role in reactor safety because it replaces the original neutron beam plug while also stopping the entire incoming neutron beam. Three aspects were therefore involved in this study, including: i) the released heat induced by both neutron and gamma radiation, ii) the swelling effect caused by both radiation and temperature increases in the steel and iii) the radioactivity induced by neutron radiation in the steel plug. An MCNP6.2 model for the TRIGA Mark-II reactor was used to calculate the neutron spectrum inside the NB1 beam tube at the inlet part of the steel plug. A gamma spectrum of a 900 MW PWR reactor was used as input to account for the gamma radiation's effects on the steel plug. In order to select a convenient steel, two investigations were carried out for two grades of steel, namely mild steel (E235) and 304L stainless steel (SS304L). The results were calculated using an in-house FORTRAN-based program and validated using COMSOL, SPECTER codes, and “Neutron Activation and Scattering Calculator” tools.The results revealed that both the E235 and 304L steels are convenient from a safety point of view, although the E235 steel is preferred at the decommissioning stage.