We report new measurements on photoneutron spectra from graphite, glucose, and melamine, revealing distinct signatures corresponding to carbon, oxygen, and nitrogen individual elements. Using a 23-MV electron linear accelerator (LINAC) and EJ-309 liquid scintillators with advanced pulse shape discrimination and pile-up rejection algorithms, we successfully detected fast neutrons from photo-nuclear (gamma,Xn) reactions within an intense pulsed photon field. Energy deposition from fast neutrons was unfolded using two well-known independent algorithms ML-EM and GRAVEL. Our findings indicate discrepancies between the experimental results and Monte-Carlo simulations performed with the widely-used code MCNP6, highlighting the need for new data in order to improve the models used for the simulation of photoneutron production. These results have significant implications for various nuclear physics applications, including electron accelerator facilities decommissioning, illicit material detection for homeland security, and global radiotherapy patient dosimetry including neutron dose.

Active photon interrogation (API) has been used for a long time in the detection of special nuclear materials and the characterization of nuclear waste, primarily relying on neutron counting from photo-fission reactions. However, recent advancements have opened new ways for extending the capabilities of API techniques. In this study, we introduce a novel approach aimed at broadening the scope of API by incorporating neutron spectrometry with an organic scintillator to unveil the signatures of light elements like nitrogen, oxygen, and carbon. These elements are commonly associated with conventional explosives, narcotics, and chemical weapons and can be identified through their photo-neutron spectra. This endeavor presents a significant challenge due to the intense and pulsed nature of the photon flux when using electron LINACs as interrogation sources. Our method entailed the utilization of a 22-MV electron linear accelerator (LINAC) in conjunction with a BC501A liquid scintillator, coupled with pulse shape discrimination and pile-up rejection algorithms. To assess the efficacy of our approach, we subjected to irradiation melamine powder (C 3 N 6 H 6 ), a simulant for conventional explosives from the point of view of nitrogen content. The results of our investigation are very promising. We successfully detected fast neutrons originating from (γ,Xn) reactions, despite mixed short-pulse fields of photon and neutron radiation characterized by intense photon flashes. Moreover, we achieved the unfolding of energy deposited in the detector, enabling the extraction of photo-neutron spectra that highlight distinct nitrogen signatures from (γ,pn) reactions. This pioneering work represents the first experimental proof-of-concept for leveraging photo-neutron spectrometry within API techniques, offering a promising alternative for the enhanced detection of illicit materials.

The production of neutrons in photon-induced nuclear reactions in the giant-dipole-resonance energy domain remains a topic of high interest for various applications, including the activation and decommissioning of electron accelerator facilities, the detection of illicit materials for homeland security, and the evaluation of neutron dose received by patients during radiotherapy treatments. General-purpose Monte-Carlo (MC) simulation codes for particle transport are intensively used to account for photoneutron production in these applications. However, due to the current scarcity of measured photoneutron energy spectra in the literature, experimental validation of MC-simulated photoneutron energy distributions is not always feasible. Therefore, a critical benchmark among simulation results from various MC codes presently appears as the only option to systematically assess their capabilities in accurately simulating photoneutron production for nuclear reactions of interest. In this work, neutron energy spectra from several targets under irradiation by 20 MeV photons are simulated, employing various state-of-the-art MC codes (FLUKA, Geant4, MCNP6, and PHITS) in their default or generally employed settings. A detailed analysis of the simulated neutron spectra allows one to not only assess the performance of various MC codes in applications such as those mentioned above, but also to partially gauge the incurred systematic uncertainty, and to highlight the present need for more comprehensive evaluated nuclear data in this domain. Ultimately, this work suggests that more prudence is required when using MC codes for applications where photonuclear reactions play a dominant role and where not only the production rate but also the energy spectrum of the emitted neutrons matters.

High-energy photon interrogation has established itself as a valuable tool for detecting special nuclear materials and characterizing nuclear waste. Previous research predominantly uses around 9-MV linear electron accelerators (LINACs) as photon sources and limited exploration has been conducted on the use of organic scintillators to determine the energy deposited in the detector and to separate photon and neutron radiation, crucial when the photon interrogation is based on the measurement of the neutron emission. The challenge arises from the intense photon flux typically produced by electron accelerators, resulting in issues such as pulse pile-up, detector saturation, and a suboptimal signal-to-background ratio. This study aims to extend the applicability of the conventional Active Photon Interrogation (API) techniques by introducing a novel method enabling the detection, in addition to nuclear materials, of light elements—specifically nitrogen, oxygen, and carbon—known to be present in conventional explosives, narcotics, and chemical weapons. The approach relies on active photon interrogation at high energies above 12 MeV, coupled with photoneutron spectrometry. Using a 22-MV electron LINAC, pulse shape discrimination with an organic liquid scintillator demonstrated promising performance. Our results highlight that the conventional pulse shape discrimination capabilities and rapid time-scale operation of organic scintillators enable the detection of fast neutrons from (γ,Xn) reactions, even in a mixed short-pulsed field of photon and neutron radiation with intense photon flashes. This exploration of the initial experimental aspects of photoneutron detection induced by high-energy photons establishes a foundation for a promising new method for the detection of illicit materials.

Induced radioactivity in particle accelerators is currently not sufficiently addressed, particularly for radiotherapy electron LINACs when the activation occurs via secondary neutrons created in photo-nuclear reactions. Methodologies based on Monte-Carlo simulations coupled with activation calculation codes are often used to address this issue. Their accuracy, which is potentially affected by the limited capabilities of the calculation tools to simulate nuclear reactions at the origin of the materials activation, can be deeply analyzed only through comparisons with experimental values but the latter are not widely available. New macroscopic data for the activity induced by neutrons in the materials commonly present in medical electron LINACs are presented. Neutron-induced activation has been measured by sample irradiation at SPIRAL2/NFS facility in accurately characterized configurations. Experimental results were compared to the simulations predictions allowing to assess the precision that can be achieved by a fully simulation-based methodology, mainly related to the energy-dependent reaction cross-sections.

The detection of illicit materials is a critical task in the field of homeland security, as international trade has contributed to the increase of smuggling activities. Nonintrusive on-site inspections are crucial in this context, but the current active interrogation methods have limitations. Neutron-induced reactions have been used, but the measurement of gamma spectra is complex due to background noise. Active photon interrogation methods have also been overlooked but they are currently limited to actinides detection using photo-fission reactions. This work presents a novel method for the detection of illicit materials based on active photon interrogation and photo-neutron spectrometry. This approach extends the application of active photon interrogation by including the detection of conventional explosives, narcotics, and chemical weapons based on the use photo-nuclear reactions to determine the content of light elements such as nitrogen, oxygen, and carbon. Monte-Carlo codes are the main tool used to simulate this process for the application need. However, because of the lack in the present literature of measured neutron spectra, the experimental validation of the simulations is not straight forward. At present, benchmarking the Monte-Carlo codes seems to be the sole option for testing their ability to accurately simulate photo-neutron production and spectra for the nuclear reactions of interest. Simultaneously, we designed a test bench based on a linear accelerator to generate photons, induce photonuclear reactions, and acquire photo-neutron spectra. This study on the fundamental aspects of photo-neutron production lays the groundwork for a promising new detection method for illicit materials.

The whole treatment process undergone by patients in clinics with Volumetric Modulated Arc Therapy (VMAT) can be tested by implementing 3D end-to-end (E2E) quality assurance with gel dosimetry. In this work, a 3D E2E test was performed in a head phantom for the verification of a VMAT treatment, using FXG (Fricke-Xylenol orange-Gelatin) gel dosimetry and a newly developed dual-wavelength reading method on a cone-beam optical CT scanner. This dosimetric method intends to enable accurate measurements in the out-of-field zone and in the tumor volume, with an effective dose range up to 10 Gy. CT images of the phantom with a gel flask were used to create a treatment plan with a brain tumor of complex shape. A very good agreement between 90 %, 80 %, 60 % and 40 % isodose curves and high 3D γ passing rates (2%/2mm) of 98.6 % and 96.7 % between measured and computed dose maps showed that E2E tests can be successfully implemented with this novel dosimetric method.

Purpose:The intensive use of Cone-Beam Computed Tomography (CBCT) during radiotherapy treatments raise some questions about the dose to healthy tissues delivered during image acquisitions. We hence developed a Monte Carlo (MC)-based tool to predict doses to organs delivered by the Elekta XVI kV-CBCT. This work aims at assessing the dosimetric accuracy of the MC tool, in all tissue types.Methods:The kV-CBCT MC model was developed using the PENELOPE code. The beam properties were validated against measured lateral and depth dose profiles in water, and energy spectra measured with a CdTe detector. The CBCT simulator accuracy then required verification in clinical conditions. For this, we compared calculated and experimental dose values obtained with OSL nanoDots and XRQA2 films inserted in CIRS anthropomorphic phantoms (male, female, and 5-year old child). Measurements were performed at different locations, including bone and lung structures, and for several acquisition protocols: lung, head-and-neck, and pelvis. OSLs and film measurements were corrected when possible for energy dependence, by taking into account for spectral variations between calibration and measurement conditions.Results:Comparisons between measured and MC dose values are summarized in table 1. A mean difference of 8.6% was achieved for OSLs when the energy correction was applied, and 89.3% of the 84 dose points were within uncertainty intervals, including those in bones and lungs. Results with XRQA2 are not as good, because incomplete information about electronic equilibrium in film layers hampered the application of a simple energy correction procedure. Furthermore, measured and calculated doses (Fig.1) are in agreement with the literature.Conclusion:The MC-based tool developed was validated with an extensive set of measurements, and enables the organ dose calculation with accuracy. It can now be used to compute and report doses to organs for clinical cases, and also to drive strategies to optimize imaging protocols.

L'objet de cette étude est de proposer une solution pour répondre à la demande émise par les fabricants de dosimètres et les exploitants du secteur nucléaire pour disposer de faisceaux de photons de haute énergie (6 MeV à 9 MeV) afin de procéder à la caractérisation des dosimètres (test de type) en vue de leur mise sur le marché et de les étalonner.Les installations de production de rayonnements photoniques de haute énergie sont des installations « lourdes » et très rares (accélérateur de protons, réacteurs nucléaires type piles piscines...).L'utilisation d'un accélérateur médical permet de mutualiser les installations entre la radioprotection et la radiothérapie et de diminuer les coûts d'exploitation.Dans un premier temps, nous avons défini (par simulations de type Monte-Carlo) puis réalisé un ensemble cible de conversion électrons/photons-atténuateur-égalisateur, qui permet l'obtention d'un faisceau homogène de photons de haute énergie (énergie moyenne pondérée par la fluence égale à 6,17 MeV) pour la radioprotection à partir d'un faisceau d'électrons de 18 MeV, fourni par l'accélérateur linéaire médical du LNE-LNHB.Le faisceau ainsi obtenu est homogène en termes de kerma dans l'air sur une surface de (30 × 30) cm 2 à 1 m.Dans un deuxième temps, nous avons fabriqué, assemblé et caractérisé deux chambres d'ionisation à cavité en graphite pour réaliser les mesures ionométriques.Pour l'une de ces chambres, nous avons mesuré le volume de collection des charges permettant ainsi de l'utiliser en tant qu'étalon primaires.L'autre chambre d'ionisation étant un étalon de transfert, elle a été étalonnée dans un faisceau de photons issu d'une source de 60 Co et dans le faisceau de photons de haute énergie pour la radioprotection.Les mesures effectuées avec les chambres d'ionisation ont permis d'évaluer la valeur du débit de kerma dans l'air dans le faisceau de photons de haute énergie pour la radioprotection : celleci couvre une gamme entre 80 mGy•h -1 et 210 mGy•h -1 , ce qui est compatible avec les besoins dans ce domaine.Enfin, nous avons calculé à l'aide de simulations de type Monte-Carlo des coefficients de conversion du kerma dans l'air vers les équivalents de dose pour des énergies de photons discrètes de 10 keV à 22,4 MeV dans des configurations géométriques spécifiques et pour la distribution spectrale de la fluence produite sur le LINAC du LNE-LNHB.

PURPOSEThe intensive use of Cone-Beam Computed Tomography (CBCT) during radiotherapy treatments raise some questions about the dose to healthy tissues delivered during image acquisitions. We hence developed a Monte Carlo (MC)-based tool to predict doses to organs delivered by the Elekta XVI kV-CBCT. This work aims at assessing the dosimetric accuracy of the MC tool, in all tissue types.METHODSThe kV-CBCT MC model was developed using the PENELOPE code. The beam properties were validated against measured lateral and depth dose profiles in water, and energy spectra measured with a CdTe detector. The CBCT simulator accuracy then required verification in clinical conditions. For this, we compared calculated and experimental dose values obtained with OSL nanoDots and XRQA2 films inserted in CIRS anthropomorphic phantoms (male, female, and 5-year old child). Measurements were performed at different locations, including bone and lung structures, and for several acquisition protocols: lung, head-and-neck, and pelvis. OSLs and film measurements were corrected when possible for energy dependence, by taking into account for spectral variations between calibration and measurement conditions.RESULTSComparisons between measured and MC dose values are summarized in table 1. A mean difference of 8.6% was achieved for OSLs when the energy correction was applied, and 89.3% of the 84 dose points were within uncertainty intervals, including those in bones and lungs. Results with XRQA2 are not as good, because incomplete information about electronic equilibrium in film layers hampered the application of a simple energy correction procedure. Furthermore, measured and calculated doses (Fig.1) are in agreement with the literature.CONCLUSIONThe MC-based tool developed was validated with an extensive set of measurements, and enables the organ dose calculation with accuracy. It can now be used to compute and report doses to organs for clinical cases, and also to drive strategies to optimize imaging protocols.

As an example, differences in PPD and NPD, for 3D-CRT and IMRT in low and high energies, are shown in the table.Taking into account leakage, field size and MU, an average increase in PPD values of 8.6% and 12.6% has been obtained for Varian and Elekta linacs with respect to Siemens, when considering for the here studied 3D-CRT treatment in 6 MV.However, a decrease in 19% was noticed when using FFF mode.

In this work, we present the results of the first part of a research project aimed at offering a complete response to dosimeters providers and nuclear physicists’ demands for high-energy (6 – 9 MeV) photon beams for radiation protection purposes. Classical facilities allowing the production of high-energy photonic radiation (proton accelerators, nuclear reactors) are very rare and need large investment for development and use. A novel solution is proposed, consisting in the use of a medical linear accelerator, allowing a significant decrease of all costs.Using Monte Carlo simulations (MCNP5 and PENELOPE codes), a specifically designed electron-photon conversion target allowing for obtaining a high energy photon beam (with an average energy weighted by fluence of about 6 MeV) has been built for radiation protection purposes. Due to the specific design of the target, this “realistic” radiation protection high-energy photon beam presents a uniform distribution of air kerma rate at a distance of 1 m, over a 30 × 30 cm2 surface. Two graphite cavity ionizing chambers for ionometric measurements have been built. For one of these chambers, the charge collection volume has been measured allowing for its use as a primary standard. The second ionizing chamber is used as a transfer standard; as such it has been calibrated in a 60Co beam, and in the high energy photon beam for radiation protection.The measurements with these ionizing chambers allowed for an evaluation of the air kerma rate in the LINAC based high-energy photon beam for radiation protection: the values cover a range between 36 mGy/h and 210 mGy/h, compatible with radiation protection purposes.Finally, using Monte Carlo simulations, conversion coefficients from air kerma to dose equivalent quantities have been calculated in the range between 10 keV and 22.4 MeV, for the spectral distribution of the fluence corresponding to the beam produced by the linear accelerator of the LNE-LNHB.

Purpose/Objective: Cone-Beam Computed Tomography (CBCT) is progressively more used in clinical practice to ensure precision in target localization and patient positioning required by new radiotherapy treatment techniques. However, intensive use of image guidance procedures could add a significant extra dose to normal tissues and potentially amplify the risk for patients to develop radiation-induced cancer. Therefore, there is an increasing interest to evaluate the dose delivered by CBCT scans. The most accurate tool to evaluate this imaging dose is the Monte Carlo (MC) method. To this end, this study aims at developing a MC-based dose calculation tool to compute the imaging dose, and to validate it in pre-clinical conditions against dosimetric measurements.

The process of design of building composites, like concrete is a complex one and involves many aspects like physical and mechanical properties, durability, shielding efficiency, costs of production and dismantlement etc. There are plenty of parameters to optimize and computer tools can help to choose the best solution. A computer aided design plays an important role nowadays. It becomes more accurate, faster and cheaper, so laboratories often apply computer simulation methods prior to field testing. In case of nuclear engineering, the radiation shielding problems are of much importance, because safety of such facilities is a key point. In this article the most effective methods for neutron shielding studies based on Monte-Carlo simulations of neutron transport and nuclide activation studies in concrete are presented. Two codes: MCNPX and CINDER'90 are extensively used to compare the shielding efficiency of commonly used concretes and to study the influence of concentration of B, Ba and Fe elements on shielding efficiency.

Inelastic neutron scattering for C-12, Fe-58, Y-89 and Pb-208 have been measured at 96 MeV at the The Svedberg Laboratory in Uppsala and double-differential cross sections are reported. Data cover an excitation energy range of 0-45 MeV and the angular intervals are 28 - 58 degrees for C-12, 26 - 65 degrees for Fe-58 and 26 - 52 degrees for Y-89 and Pb-208. In this experiment, neutron detection is based on conversion to protons in an active scintillator converter. An analysis technique in which the neutron spectra have been obtained through a folding procedure using the response of the detector system has been used. The results are compared to and are in reasonable agreement with several model predictions and with inelastic neutron scattering data at 65 MeV from University of California, Davis, USA.

Double-differential cross sections for neutron production were measured in 96-MeV neutron-induced reactions at The Svedberg Laboratory in Uppsala, Sweden. Measurements for Fe and Pb targets were performed using two independent setups: DECOI-DEMON, time-of-flight telescope dedicated to the detection of emitted neutrons with energies between a few and 50 MeV and CLODIA-SCANDAL device devoted to measuring emitted neutrons with energies above 40 MeV. Double-differential cross sections were measured for an angular range between 15 and 98 deg and with low-energy thresholds (approximate to 2 MeV). Angular and energy distributions and total neutron emission cross sections have been obtained from those measurements. Results have been compared with predictions given by different models included in several transport codes (MCNPX, GEANT, TALYS, PHITS, and DYWAN) and with other experimental data (the EXFOR database).

Double-differential cross sections for neutron production were measured in 96-MeV neutron-induced reactions at The Svedberg Laboratory in Uppsala, Sweden. Measurements for Fe and Pb targets were performed using two independent setups: DECOI-DEMON, time-of-flight telescope dedicated to the detection of emitted neutrons with energies between a few and $50\phantom{\rule{0.16em}{0ex}}\text{MeV}$ and CLODIA-SCANDAL device devoted to measuring emitted neutrons with energies above $40\phantom{\rule{0.16em}{0ex}}\text{MeV}$. Double-differential cross sections were measured for an angular range between 15 and 98 deg and with low-energy thresholds ($\ensuremath{\approx}$2 MeV). Angular and energy distributions and total neutron emission cross sections have been obtained from those measurements. Results have been compared with predictions given by different models included in several transport codes (MCNPX, GEANT, TALYS, PHITS, and DYWAN) and with other experimental data (the EXFOR database).