Fast Neutron Detection Research Articles

Particles Detection System with CR-39 Based on Deep Learning

We present a novel method that we call FAINE, fast artificial intelligence neutron detection system. FAINE automatically classifies tracks of fast neutrons on CR-39 detectors using a deep learning model. This method was demonstrated using a LANDAUER Neutrak® fast neutron dosimetry system, which is installed in the External Dosimetry Laboratory (EDL) at Soreq Nuclear Research Center (SNRC). In modern fast neutron dosimetry systems, after the preliminary stages of etching and imaging of the CR-39 detectors, the third stage uses various types of computer vision systems combined with a manual revision to count the CR-39 tracks and then convert them to a dose in mSv units. Our method enhances these modern systems by introducing an innovative algorithm, which uses deep learning to classify all CR-39 tracks as either real neutron tracks or any other sign such as dirt, scratches, or even cleaning remainders. This new algorithm makes the third stage of manual CR-39 tracks revision superfluous and provides a completely repeatable and accurate way of measuring either neutrons flux or dose. The experimental results show a total accuracy rate of 96.7% for the true positive tracks and true negative tracks detected by our new algorithm against the current method, which uses computer vision followed by manual revision. This algorithm is now in the process of calibration for both alpha-particles detection and fast neutron spectrometry classification and is expected to be very useful in analyzing results of proton-boron11 fusion experiments. Being fully automatic, the new algorithm will enhance the quality assurance and effectiveness of external dosimetry, will lower the uncertainty for the reported dose measurements, and might also enable lowering the system’s detection threshold.

Boron nitride neutron detector with the ability for detecting both thermal and fast neutrons

The detection of fast neutrons is regarded technically challenging because the interaction probability of fast neutron with matter is extremely low. Based on our recent development of hexagonal boron nitride (BN) semiconductor thermal neutron detectors with a record high efficiency of 59%, we report here the feasibility studies of BN detectors for detecting fast neutrons. A BN detector with a detection area of 2.1 cm2 was fabricated from a 90 μm thick BN epilayer. In the presence of a bare Cf-252 source emitting fast neutrons ranging from 1 to 9 MeV, the detection efficiency was estimated to be about 0.1%. The measured mean free path of fast neutron in BN is about 7.6 cm. Together with the capability of BN for thermal neutron detection, the present results indicate that by incorporating BN with a large thickness, BN neutron detectors are expected to possess the unique capability of directly detecting thermal to fast neutrons as well as outstanding features resulting from the ultrawide bandgap of BN. The identification of a single material that is sensitive to both thermal and fast neutrons is valuable for the development of novel neutron detection technologies.

The polysiloxane-based scintillator for measurements of fast neutron spectra in nuclear physics experiments

Next generation radioactive ion beam (RIB) facilities among which the SPES facility in construction at INFN-LNL require selective detection apparatuses of high resolution and efficiency as well as high granularity and then the highest covering of the solid angle. On this line the fast neutron detection still represents an uneasy task. Among the organic scintillators, the new polysiloxane-based scintillators have appealing features for measurements of neutron spectra in RIBs applications. In this work a prototype of polysiloxane-based scintillator was fully tested to gamma, alfa and neutron radiation. The scintillator calibration was studied by comparing more than one method and the pulse shape discrimination capabilities were appropriately assessed. Three fast neutron spectra were produced at the INFN-LSN tandem accelerator by means of the 7Li(p,n)7Be reaction at different energies of the incident protons. The measurements of the produced neutron yield together with theoretical estimations based on FLUKA simulations allowed first measurements of the detection efficiency. The fast response, non-toxicity, non-flammability, cheapness and high radiation resistance together with good efficiency and pulse shape capabilities make these scintillators an interesting detector for fast neutron spectroscopy in applications with RIBs.

Study of silicon photomultipliers (SiPM) with organic scintillator for neutron diagnostics of thermonuclear plasma

The spectrometry of neutrons produced by fusion reactions of plasmatic ions is the most powerful neutron diagnostic tool for monitoring reactor operating power, temperature and concentration of ions. Currently, new generations of silicon photomultipliers (SiPMs) are being used in several light detection fields, including nuclear domain; they have performances similar to conventional photomultipliers tubes (PMTs), while benefiting advantages of solid-state technology such as insensitivity to magnetic and electric fields, excellent temperature stability, robustness, low operating voltage, small size, and low cost. Consequently, they could be a useful device in neutron spectrometer based on recoil proton method for neutron diagnostics of hot plasmas. In this paper, we have demonstrated SiPMs capabilities to be used for fast neutron detection as well as their dynamic range for thermonuclear fusion neutron spectrometry (14 Mev). The responses of SiPMs having different sizes of active areas and microcells manufactured by Ketek and SensL have been studied. Excellent pulse shape discrimination of PuBe source radiations by SiPMs combined with a stilbene crystal has been proven; the figure of merit has reached 3.33. The study has also allowed the determination of the size parameters of SiPMs that are suitable for neutron diagnostics of thermonuclear plasmas.

Neutron-γ discrimination with organic scintillator crystal: 9-Phenylcarbazole (9-PCz) grown by Bridgman – Stockbarger method

Organic scintillator crystal 9-Phenylcarbazole (9-PCz) has been grown using Bridgman -Stockbarger technique. The crystal structure, lattice parameter and bond angle values are measured from single-crystal X-ray diffraction (SXRD) analysis. C–H inplane bending and out of plane bending and skeletal vibrations of 9-PCz molecule were identified from vibrational spectral analysis. UV–visible NIR spectral study shows that the crystal exhibits around 50% of transmittance in the infrared region and the direct optical bandgap energy is calculated to be 3.36 eV. Thermal properties of grown 9-PCz material were measured using thermogravimetric and differential thermal analyses (TG-DTA). The photoluminescence (PL) measurements show two emission bands with a maximum peak at 365 nm and a shoulder peak at 381 nm. X-ray induced luminescence spectrum of 9-PCz crystal exhibits a maximum emission peak at 381 nm. Scintillation decay time measurement shows the major component of 18 ns decay time. The pulse shape discrimination (PSD) capability of the grown crystal sample was studied for the signals induced by α-particles and γ-rays from 241Am and 137Cs sources, respectively. The figure of merit (FOM) is found to be 2.69. The preliminary results showed that the present studied organic crystal (9-PCz) scintillator can be considered in the field of fast neutron detection application.

Optimization of fast neutron and X-ray pulse shape discrimination (PSD) using an EJ276G scintillator in high radiation mixed conditions

Organic crystalline, liquid, and plastic scintillators with low Z-number materials are commonly used in fast neutron detectors. Pulse shape discrimination (PSD) is used to distinguish neutrons from X-rays because these detectors are affected by X-rays due to Compton scattering during fast neutron measurement. PSD was performed with a 1 × 1 × 3 cm3 EJ276G plastic scintillator, SiPM, and DAQ (10-bit resolution, 400 MHz) using the charge comparison method, which compares the total charge (Q body) and the delayed charge (Q tail) from the peak. Most studies have been conducted under laboratory conditions, such as with 252Cf or 241Am-Be sources. This study will perform PSD in a 15 MeV electron accelerator with a total flux of 6.72 × 1014 #/sec and an X-ray-to-neutron ratio of up to 4071:1. The PSD was optimized before the measurement in high flux conditions because it was difficult to perform PSD due to the pile-up effect in these conditions. Optimization focused on the figure of merit (FoM), which is an index of PSD performance. To distinguish neutrons from X-rays under these conditions, lead shielding is necessary to reduce the X-ray-to-neutron ratio. We performed Monte Carlo N-Particle Transport Code (MCNP6) simulations to determine the optimal shielding thickness. Fast neutrons interact with lead due to its high density, which results in small neutron energy loss and direction changes by scattering. This effect can affect other pixels as noise. We plan to evaluate the neutron images under high X-ray flux conditions by comparing the images of the MCNP6 simulation results and the measurement results.

Enhancement of Fast Neutron Detection in Liquid Scintillator Detectors

Organic liquid scintillators, such as EJ-309, are capable of detecting fast neutrons and discriminating gamma rays through pulse shape. Higher detection efficiency is a common objective for detector designs and research. This paper describes two methods to enhance fast neutron detection by increasing neutron collection and reducing gamma-ray interference. Neutron collection can be increased by using strong scattering material to reflect neutrons toward scintillators. Gamma-ray interference can be reduced by using heavy material to shield gamma rays; such a material could have a minimal impact on neutron detection because neutrons and gamma rays have different interaction cross sections. In this work, both effects were investigated, experimentally and by simulation. Using a graphite reflector with simple geometry, the fast neutron detection was measured to have an increase of 9%, and simulations predicted an approximately 50% increase for optimized geometry. Using a lead shielding of 8-mm thickness, the neutron detection with a Pu source was measured to have a factor of 2 increase. These methods could be useful when cost-effective and highly efficient fast neutron detection is desired.

Concept of a fast neutron detector based on 10B-RPCs

We propose an alternative approach for the detection of fast neutrons in the energy range from 10-4 to 5 MeV based on 10B-RPCs (hybrid double-gap Resistive Plate Chambers with 10B4C neutron converters) surrounded by a polyethylene moderator. The detection efficiency as a function of the neutron energy is obtained in Monte Carlo simulations performed with the Geant4 toolkit for several detector configurations. The thickness of the neutron converter is optimized for the maximum efficiency. The results show that for this type of detector it is possible to obtain an average detection efficiency larger than 50% with a weak dependence on the neutron energy. The dark count rate and gamma sensitivity are also discussed.

Quantifying water in spent fuel assemblies with neutrons: A simulation-based approach

A simulation-based study concerning three non-destructive approaches by which water in spent nuclear fuel assemblies might be quantified with neutrons is described. Three fuel types have been considered: thirty-six spent Advanced Gas-cooled Reactor (AGR) fuel pins contained in a stainless-steel can; a prototype fast reactor (PFR) spent fuel assembly and a light water reactor (LWR) spent fuel assembly – with the PFR and LWR assemblies containing mixed oxide fuels. The three approaches are investigated with MCNP5 based on neutron interrogation: fast neutron detection of the perturbed fast neutron flux and two approaches based on the 2.223 MeV γ-ray photon emission resulting from the 1H(n,γ)2H capture reaction, stimulated with moderated and unmoderated neutrons. For each of these approaches the following perspectives have been considered: neutron transmission, the influence of radiation emitted by the associated spent fuel inventory, and the dependencies on water quantity and location. The moderated γ-ray assay technique is observed to return the most significant distinction between scenarios with and without water in the fuel assemblies, notwithstanding the need for efficiency response functions to be overlaid on the neutron models as part of the interpretation of the MCNP model results. Water present in all of the spent fuels considered is observed to perturb the incident neutron flux to a degree significant within the simulation uncertainties. The AGR and PFR cases are not undermined by the intrinsic neutron field from the fuel; whereas for the LWR-MOX case, the simulations suggest that this will limit its potential. Successful detection of water quantities down to 10 g is anticipated for AGR, whereas reduced mass sensitivity is forecast for PFR and LWR-MOX, where it is assumed that the water will be more dispersed. Water located in fewer locations is observed to be harder to discern, suggesting that small, localised quantities of water could pose a challenge for these techniques.

Light output quenching in response to deuterium-ions and alpha particles and pulse shape discrimination in deuterated trans-stilbene

We characterized the light output response of a new 140 cm3 stilbene-d12 crystal up to 14.1 MeV neutron energies using a coincidence neutron scattering system. We also characterized its light output response to alpha particles in the 5 to 6 MeV energy range. The excellent PSD capability of the stilbene-d12 detector allowed us to select light pulses produced by particles of increasing ionization density, namely electrons, protons, deuterium-ions, and alpha particles. The measured fast decay component of the light pulses is increasingly quenched as the ionization density of the particle in the crystal increases. Consistently with this finding, the Birks’ quenching parameter of alpha particles is approximately 8.5 times larger compared to the quenching of deuterium ions, produced by neutron scattering interactions. The reported experimental characterization will allow high-fidelity modeling of the detector enabling its application for fast-neutron detection and spectroscopy in nuclear physics, radiation protection, nuclear security, and non-proliferation.

Improvements in scintillation performance of Tl2LaCl5:5%Ce single crystals via Sr2+, Ba2+ and Ca2+ co-doping

High detection efficiency for X- and γ-rays, fast neutron detection capability, and other excellent scintillation performances of Tl2LaCl5 (TLC) make it a potential radiation detector for applications in various industrial and research field.

Modular next generation fast-neutron detector for portal monitoring

Modular next generation fast-neutron detector for portal monitoring

Hydrogen-Rich 2D Halide Perovskite Scintillators for Fast Neutron Radiography.

A fast neutron has strong penetration ability through dense and bulky objects, which makes it an ideal nondestructive technology for detecting voids, cracks, or other defects inside large equipment. However, the lack of effective fast neutron detection materials limits its application. Perovskites have shown excellent optical properties in many areas, but they are absent from fast neutron detection imaging because they cannot directly absorb fast neutrons and emit luminescence. Here, we demonstrate a hydrogen-rich long-chain organic amine modified two-dimensional (2D) perovskite fast neutron scintillator, Mn-(C18H37NH3)2PbBr4(Mn-STA2PbBr4). Its hydrogen density can reach 9.51 × 1028 m-3, and the photoluminescence quantum yield can reach 58.58%, so it is possible to integrate fast neutron absorption and luminescence into a single compound. More importantly, Mn-STA2PbBr4 can be made into a large-area self-supporting fast neutron scintillator plate with satisfactory spatial resolution (0.5 lp/mm (lp: line pairs)). This strategy provides a simple and promising choice for fast neutron scintillator nondestructive testing.

RIPTIDE: a novel recoil-proton track imaging detector for fast neutrons

Neutron detectors are an essential tool for the development of many research fields, as nuclear, particle and astroparticle physics as well as radiotherapy and radiation safety. Since neutrons cannot directly ionize, their detection is only possible via nuclear reactions. Consequently, neutron-based experimental techniques are related to the detection of charged particle or electromagnetic radiation originating from neutron-induced reactions. The study of fast neutrons is often based on the neutron-proton elastic scattering reaction. In this case, the ionization induced by the recoil protons in a hydrogenous material constitutes the basic information for the design and development of neutron detectors. Although experimental techniques have continuously improved and refined, so far, proton-recoil track imaging is still weak in laboratory rate environments because of the extremely small detection efficiency. To address this deficiency, we propose a novel recoil-proton track imaging system in which the light deriving from a fast scintillation signal is used to perform a complete reconstruction in space and time of the event. In particular, we report the idea of RIPTIDE (RecoIl Proton Track Imaging DEtector): an innovative system which combines a plastic scintillator coupled to imaging devices, based on CMOS technology, or micro channel plate sensors. The proposed apparatus aims at providing neutron spectrometry capability by stereoscopically imaging the recoil-protons tracks, correlating the spatial information with the time information. RIPTIDE intrinsically enable the online analysis of the ionization track, thus retrieving the neutron direction and energy, without spoiling the overall efficiency of the detection system. Finally, the spatial and topological event reconstruction enables particle discrimination — a crucial requirement for neutron detection — by deducing the specific energy loss along the track.

Comparison of Neutron Detection Performance of Four Thin-Film Semiconductor Neutron Detectors Based on Geant4.

Third-generation semiconductor materials have a wide band gap, high thermal conductivity, high chemical stability and strong radiation resistance. These materials have broad application prospects in optoelectronics, high-temperature and high-power equipment and radiation detectors. In this work, thin-film solid state neutron detectors made of four third-generation semiconductor materials are studied. Geant4 10.7 was used to analyze and optimize detectors. The optimal thicknesses required to achieve the highest detection efficiency for the four materials are studied. The optimized materials include diamond, silicon carbide (SiC), gallium oxide (GaO) and gallium nitride (GaN), and the converter layer materials are boron carbide (BC) and lithium fluoride (LiF) with a natural enrichment of boron and lithium. With optimal thickness, the primary knock-on atom (PKA) energy spectrum and displacements per atom (DPA) are studied to provide an indication of the radiation hardness of the four materials. The gamma rejection capabilities and electron collection efficiency (ECE) of these materials have also been studied. This work will contribute to manufacturing radiation-resistant, high-temperature-resistant and fast response neutron detectors. It will facilitate reactor monitoring, high-energy physics experiments and nuclear fusion research.

Investigations of radiation damaged arranged scintillating particle composites

Composites consisting of periodically arranged scintillating particles within an acrylic (poly methyl methacrylate) matrix are excellent templates for the gamma-insensitive detection of fast neutrons. In order to study the impact of radiation damage on acrylic-based scintillating particle composites, we exposed acrylic samples to different doses of fast neutrons up to 119.7 kGy and investigated the change in optical characteristics using optical absorption spectroscopy in the 200–800 nm wavelength range. The experimental results are compared to coupled MCNP6 and optical ray-tracing (FRED) simulations, and qualitative agreement is found. Neutron-induced radiation damage in the acrylic matrix manifests as a red-shift in the ultra-violet absorption edge of the acrylic and a corresponding decrease in the light propagation efficiency, which leads to detector performance degradation. We show for the first time that the effects of radiation damage can be mitigated by the use of wavelength-shifting coatings. We predict that composites with wavelength-shifting coatings can enable neutron detectors with high tolerance against neutron-induced radiation damage, a property that is particularly desired for neutron detection in high radiation environments.

Direct Detection of Fast Neutrons by Organic Semiconducting Single Crystal Detectors

AbstractFast neutron detection is significant for neutron imaging and flux monitoring but cannot be directly achieved by inorganic semiconductors. The traditional detection is mainly mediated by an organic scintillator and a coupled photodetector, resulting in signal losses. Here, a direct detection method for fast neutrons is demonstrated based on organic semiconducting single crystals (OSSCs) detectors. Methyl 4‐hydroxybenzoate (4MHB, C6H5O‐COOCH3) and 4‐hydroxycyanobenzene (4HCB, C6H5O‐CN). The organic semiconductor acts as a fast neutron sensitive material due to its high hydrogen density, simultaneously as a semiconductor that generates the electric signal. The detectors based on 4MHB crystals can quantitatively measure the dose and energy of the fast neutron flux with a response time of 0.5 µs and detection efficiency of 78.5% cm−3. Effects of functional groups on fast neutron detection performances are also investigated as a guideline to synthesis new molecules for this purpose. Furthermore, neutron radiation effects on these detectors are investigated. Hydrogen‐related point defects are generated by fast neutrons, but device performances remain robust after irradiation of 1013n cm−2fast neutrons. This study demonstrates that OSSCs show great potential as direct fast neutron detectors and particularly have highly‐localized and tissue‐equivalent properties that benefit neutron imaging and cancer therapy applications.

Effective exploitation of a geyser bubble-chamber equipment as a background-free fast neutron detector

The MOSCAB equipment, a geyser-concept bubble-chamber originally thought for the search of dark matter in the form of WIMPs, is employed for the detection of fast neutrons. Once the background-free operating conditions are determined such that the detector is sensitive only to neutrons, which occurs when the neutron energy threshold required for nucleation is higher than approximately 2.5 MeV, the detector response to fast neutrons is investigated using a {^{241}}AmBe neutron source. Sets of detection efficiency functions are then produced via Monte Carlo simulations and post-processing, their validation being performed experimentally and discussed. Finally, the use of the detector to measure the fast neutron activity of very weak n-sources in low neutron background environments, as well as to monitor the cosmic ray variations through the neutron component of the Extensive Air Showers, is considered.

Detection sensitivity comparison of centrifugally tensioned metastable fluid detector vs Ludlum-42-49B™ for shielded & unshielded neutron source configurations

This paper presents results of neutron detection sensitivity between a ∼ 2.5 kg, non-borated Centrifugally Tensioned Metastable Fluid Detector (CTMFD) as compared to a commercial state of the art moderated, 4.5 kg He-3 based Ludlum (42-49B™) neutron detector of similar form factor. The study used: a collimated 1 Ci plutonium-beryllium (α, n) neutron source emitting 2.2 × 106 n/s. Water, concrete and lead shielding materials of thicknesses ranging from none to up to 0.3 m were used. The CTMFD as deployed was configured for detection of fast energy neutrons. Monte Carlo N-Particle Transport (MCNP) code-based simulations were conducted to account for 3-D effects and for computing cpm/mrem/h sensitivity estimates. At 0.6 MPa (6 bar) negative pressure (Pneg) state, and without benefiting from detecting epithermal neutrons, the CTMFD was found to offer up to ∼5 + times higher cpm/mrem/h sensitivity vs the Ludlum-42-49B. At Pneg ∼ 1.1 MPa (11 bar) the gain exponentially rises to ∼100× higher for the CTMFD vs Ludlum-42-49B.

Gamma-blindness & neutron detection efficiency assessments with centrifugally tensioned metastable fluid detectors in low-scatter environment

A range of tests and associated analyses were performed in a state-of-art low scatter environment to demonstrate and validate the performance of the (Medium) Centrifugally Tensioned Metastable Fluid Detector (MCTMFD) for gamma blind detection of fast and epithermal neutrons for a variety of configurations, using Cf-252 and Am-Li isotope neutron sources. All measurements were performed in the Low Scatter Room (LSR) of Radiological Exposures & Metrology Laboratory at Pacific Northwest National Laboratory (PNNL). Experiments were performed to evaluate intrinsic neutron detection efficiency, ɛint n, the intrinsic gamma-neutron detection efficiency, ɛintγn, and the gamma absolute rejection ratio for neutrons (GARRn) as a function of tensioned metastable state negative pressure, Pneg, varying from 2.5 bar towards 9 bar. The specific embodiment of the MCTMFD utilized for the experiments at PNNL included a 16 cm 3 sensitive volume configured for either fast neutron detection using Decafluoropentane (DFP) as the detection medium, or fast and thermal neutron detection (using DFP with a chemical mixture composed of natural boron). Experiments were performed with Cf-252 neutron sources ranging in intensity from 1 × 104 n/s to 3.45 × 105 n/s, an Am-Li neutron source with intensity of 2.5 × 104 n/s, used in both a bare configuration and in combination with a 30 cm OD moderating sphere of D2O, with and without a 0.5 mm Cd shell, and intense Cs-137 and Co-60 gamma sources offering dose rates ranging from 27 mR/h to 53 R/h. It was found that the MCTMFDs remained gamma-blind (ɛintγn < 10−11) even under 53 R/h gamma background; the associated intrinsic fast neutron detection efficiency (ɛint n) varied from ∼0.2% for Pneg ∼2.5 bar, ∼10% for Pneg ∼5.5 bar and, ∼30% for Pneg ∼9 bar for a Cf-252 fission spectrum. In comparison, for the softer (Am-Li) spectrum, the ɛint n varied from ∼1% for Pneg ∼5.5 bar and approached the ɛint n values for Pneg states above 7 bar. The same MCTMFD when using a borated detection fluid with 20% B-10, offered a ×10–20 improvement in ɛint n for Pneg states ranging from 4.5–5 bar, for detecting epithermal neutrons from the Am-Li source (placed within a 30 cm OD, D2O moderator with and without a 0.5 mm Cd shield).