Digital Real-Time Multiple Channel Multiple Mode Neutron Flux Estimation on FPGA-based Device

This paper presents a complete custom full-digital instrumentation device that was designed for real-time neutron flux estimation, especially for nuclear reactor in-core measurement using subminiature Fission Chambers (FCs). Entire fully functional small-footprint design (about 1714 LUTs) is implemented on FPGA. It enables real-time acquisition and analysis of multiple channels neutron's flux both in counting mode and Campbelling mode. Experimental results obtained from this brand new device are consistent with simulation results and show good agreement within good uncertainty. This device paves the way for new applications perspectives in real-time nuclear reactor monitoring

Digital Real-Time Multiple Channel Multiple Mode Neutron Flux Estimation on FPGA-based Device

This paper presents a complete custom full-digital instrumentation device that was designed for real-time neutron flux estimation, especially for nuclear reactor in-core measurement using subminiature Fission Chambers (FCs). Entire fully functional small-footprint design (about 1714 LUTs) is implemented on FPGA. It enables real-time acquisition and analysis of multiple channels neutron's flux both in counting mode and Campbelling mode. Experimental results obtained from this brand new device are consistent with simulation results and show good agreement within good uncertainty. This device paves the way for new applications perspectives in real-time nuclear reactor monitoring

Neutron/gamma discrimination enhancement: plastic scintillators high dose irradiation and recovery time

International audienceIn the context of high-energy physics experiments, particle accelerators create a significant dose of radiations, up to 106 Gy for example at the Large Hadron Collider (LHC, Cern). Control detectors, such as scintillators, are affected by these high irradiation levels. The literature mentions that the light yield of organic scintillators dramatically drops when strongly irradiated. However, the tested scintillators can recover some of their light output with time. To the best of our knowledge, only the luminescent properties of plastic scintillators were analyzed under high radiation fluxes. But, plastic scintillators are also able to discriminate fast neutrons from gamma rays. In this work, we characterized neutron/gamma discriminating as well as emissive propertiesof plastic scintillators after high dose irradiations. Two identical lab-made plastic scintillators containing a polystyrene-based matrix and two fluorophores were analyzed before and after high dose irradiation. Irradiation was performed using a Gamma-Cell 220 Excel with twelve 60Co sources and a 53.7 Gy/min dose rate at isocenter. These two scintillators were irradiated to reach a cumulative dose equal to 104 Gy.In order to measure their neutron/gamma discrimination ability, scintillators were coupled to a Hamamatsu R7724-100 photomultiplier tube and placed in front of a 252Cf source (Activity 580 kBq). The anode signal fed a digitizer. Scintillation pulses were then recorded and post-processed. A charge-comparison method was implemented and FoM was evaluated. Offlinetreatment allowed the estimation of fast and slow decay times of neutron pulses, as well as their relative intensities. In parallel, characterization of radioluminescence properties of irradiated and non-irradiated samples was performed.Results indicate a strong modification in the neutron/gamma discrimination capability before and after high dose irradiations and a redshift of the radioluminescence spectrum. In fact, a 103 Gy irradiation increases the FoM of both sensors by a factor 2.5 at least. Further, as recovery time passes after a 104 Gy cumulative dose, FoM improves for scintillators and is multiplied by 6 compared to the value at the zero dose. Thanks to evaluated decay times and relative intensities, we could infer that a strong irradiation does not produce a higher yield of triplet excited states but it impacts the slow decay time of the tested scintillator. This leads to a better neutron/gamma discrimination than at the zero dose. These observations lead us to believe that the intrinsic nature of the plastic material is modified under high dose irradiation.In this paper we present the current iteration of this ongoing work. The neutron/gamma discrimination properties are presented for both plastic scintillators and first characterization results are discussed. We show that material modification under high dose irradiation manages to an improvement in neutron/gamma discrimination opening the field to applications of very high dose measurements

Detection and quantification of copper in scrap metal by linac-based neutron activation analysis

International audienceThis paper presents the investigation carried out by CEA List and ArcelorMittal R&D in order to assess the potential of linac-based neutron activation analysis to detect and quantify copper in scrap metal. Performances are evaluated using MCNP6 and then validated experimentally using a 6 MeV linac coupled with heavy water. It is shown that (γ, n) reaction cross-sections for deuterium are likely to be undervalued in ENDF/B-VII and suggested that photoneutron production algorithms in Monte Carlo codes should be reexamined

The role of the secondary fluorophore in ternary plastic scintillators aiming at discriminating fast neutrons from gamma-rays

International audienceSince Helium-3 shortage announcement, organic scintillators play a major role in neutron detection. Our laboratory decided to focus on plastic scintillators and their ability to discriminate fast neutrons from gamma rays. In this work, we highlight the influence of the secondary fluorophore in lab-made plastic scintillators. The secondary fluorophore is generally added in the scintillating mixture to shift the emission wavelength towards the transparency domain of the material to improve its attenuation length. Thus, it is considered as a harmless molecule and is barely seen as a key criterion that could enhance the performances of the organic scintillator. In our work, we demonstrate that this molecule, even added at a small concentration (typically in the range 0.02–0.2 wt%), directly impacts the neutron/gamma discrimination ability of plastics. Not only the secondary fluorophore plays a role in self-absorption of the scintillating material, but also the couple it creates with the primary fluorophore has to be carefully chosen, as some specific triplet energy transfers between the two fluorophores can influence the neutron/gamma discrimination abilities of the plastic scintillator. Aside from classical photophysical inconveniences such as self-absorption or diffusion, the possibility that the whole, bulk material was heterogeneous in a photochemical point of view was also checked. Thus, various samples were cut from bulk monoliths and their pulse shape discrimination compared with the parent scintillator in terms of Figure of Merit and light output

First TDCR measurements at low energies using a miniature x-ray tube

International audienceDeveloped for radionuclide standardization using liquid scintillation, the Triple to Double Coincidence Ratio (TDCR) method is applied using coincidence counting obtained with a specific three-photomultiplier system. For activity determination, a statistical model of light emission is classically used to establish a relation between the detection efficiency and the experimental TDCR value. At LNE-LNHB, a stochastic approach of the TDCR modeling was developed using the Monte Carlo code Geant4. The interest of this TDCR-Geant4 model is the possibility to simulate the propagation of optical photons from their creation in the scintillation vial to the production of photoelectrons in photomultipliers. As an alternative to the use of radionuclide sources, first TDCR measurements are presented using a miniature x-ray tube closely coupled to the scintillation vial. The objective of this new set-up was to enable low-energy depositions (lower than 20 keV) in liquid scintillator in order to study the influence of both time and geometrical dependence between PMTs already observed with radioactive sources. As for the statistical TDCR model, the non-linearity of light emission is implemented in the TDCR-Geant4 model using the Birks formula which depends on the kB factor and the scintillation yield. Measurements performed with the x-ray tube are extended to the assessment of these parameters and they are tested afterwards in the TDCR-Geant4 model for activity measurements of (3)H

Preliminary TDCR measurements at low energies using a miniature x-ray tube

International audienceDeveloped for radionuclide standardization using liquid scintillation, the TDCR method (Triple to Double Coincidence Ratio) is applied using coincidence counting obtained with a detection system composed of three photomultiplier tubes. For activity determination, a statistical model of light emission is classically used to establish a relation between the detection efficiency and the experimental TDCR value. Among the usual assumptions specified for the standard TDCR model, the condition of stochastic independence between PMTs is not explicitly mentioned. The validity of this condition can be tested using a stochastic approach of the TDCR modeling based on the Geant4 simulation code. The interest of this TDCR-Geant4 model is the possibility to simulate the propagation of optical photons from their creation in the scintillation vial to the production of photoelectrons in PMTs. Previous investigations revealed the existence of stochastic dependence between PMTs of geometrical origin in the case of low-energy depositions (lower than 20 keV). Not considered in the standard model, this effect can entail non-negligible deviations on calculated detection efficiencies and in turn on activity determination

On the use of pixelated plastic scintillator and silicon photomultipliers array for coded aperture gamma-neutron imaging

International audienceWe report the investigations made on the use of pixelated plastic scintillator (PS) and silicon photomultipliers (SiPMs) array applied to coded aperture gamma-neutron imaging. Specifically, verification of the ability of a multiplexing readout to discriminate and localize neutron interactions was studied. In its intended configuration, the gamma-neutron imager design consists of a coded aperture aligned with a matrix of 12 × 12 PS each coupled to a SiPM. The coded aperture is a rank 7 modified uniformly redundant array (MURA), composed of 1.2 cm of tungsten, with a surface area of 100.4 mm × 100.4 mm and placed at 5 cm from the detector. The pixelated PS is composed of polystyrene and standard fluorophores (20 wt% PPO, 0.03 wt% POPOP) loaded with a lithium carboxylate (Li α -valerate), which allows the triple discrimination between thermal neutrons, fast neutrons, and photons. Each pixel of PS has a dimension of 3.6 mm × 3.6 mm × 3.6 mm and they are separated from each other by 0.6 mm of polytetrafluoroethylene (PTFE). The photonic and electronic readout consists of the ArrayC-30035-144P SiPM from SensL, Cork, Ireland, connected to the diode coupled charge division readout from AiT. First, this neutron imager design was modeled and simulated using the MCNP6 Monte Carlo code. The encoding capability, field of view, and spatial resolution of the neutron imager were therefore evaluated by simulation. Then, we detailed the experimental setups implemented to demonstrate the feasibility of coupling pixelated PS to SiPM to localize radioactive sources and showed the results obtained. Finally, based on this position-sensitive gamma-neutron detector, a gamma-neutron imager was prototyped and tested

Neutron/gamma discrimination and localization with pixelated plastic scintillators and SiPM dedicated multiplexing readout

International audienceThe development of instruments for measuring radioactivity and more particularly systems for characterizing and locating particles is an important issue in many fields, such as nuclear industry (gamma-neutron imaging and radiography) and medicine (scintigraphy, SPECT and PET), high-energy physics (tracking and calorimetry) and astrophysics (space observatory). These areas are not exempt from the need of technologies to reduce size and energy consumption along with the increase of durability. In this context, the use of silicon photomultipliers (SiPM), instead of a photomultiplier tube, addresses to these issues thanks to its compactness, modularity, low cost and robustness. Moreover, their assembly in a matrix form allows the position of interactions to be measured.The aim of this work is to develop a compact, scalable and position-sensitive neutron detector with high sensitivity based on a pixelated plastic scintillator (PS) and a SiPM array coupled with a multiplexing readout. The chemical composition of manufactured PS was chosen for its gamma/neutron discrimination abilities. The SiPM array used in these experiments is from SensL, the ArrayC-30035-16P . In order to minimize the number of channels to be digitized, we employed the multiplexing readout fro