Fast Neutron Detection Research Articles

A Study of Reactions with Light Nuclei Using a Position Sensitive Fast Neutron Detector

A Study of Reactions with Light Nuclei Using a Position Sensitive Fast Neutron Detector

250 μm Thick Detectors for Neutron Detection: Design, Electrical Characteristics, and Detector Performances

Solid State Detectors (SSD) are crucial for fast neutron detection and spectroscopy in tokamaks due to their solid structure, neutron-gamma discrimination, and magnetic field resistance. They provide high energy resolutions without external conversion stages, enabling compact array installations in the harsh environment of a tokamak. Research comparing diamond and 4H-SiC detectors highlights thickness as a key efficiency factor. A 250 μm SiC epilayer with low doping, grown using a high-growth-rate process, exhibits sharp interfaces and minimal defects, essential for neutron detectors. The study evaluates detector designs, and performance using a 4H-SiC substrate. Various detector designs, such as Schottky diodes and p/n diodes, are assessed via I-V and C-V measurements, addressing high depletion voltage challenges. Preliminary neutron irradiation tests validate detector functionality, energy resolution and confirming detector reliability.

Performance stability of plastics for neutron-gamma pulse shape discrimination

The introduction of the first commercially available plastic scintillators with pulse shape discrimination (PSD) offered by Eljen Technology marked progress towards potentially replacing liquid scintillators in neutron detection. However, use of these plastics over several recent years has revealed an important flaw in these materials: the eventual degradation of scintillation light output and PSD performance. Studies described in this paper considered possible reasons for this degradation. Experiments conducted with numerous lab-prepared and commercial EJ-276 samples showed that the main factor affecting the instability is oxidation that involves highly reactive radicals generated during the polymerization process or from the further breakdown of polymer chains under oxygen/air exposure. Based on the obtained results, the stability of scintillation performance for PPO (2,5-Diphenyloxazole)-based PSD plastics has been improved through modifications of the composition via the utilization of scintillation dyes and compounds with antioxidant properties that diminish the effects of oxidation. Elements of these studies were used in the commercial production of the most recent EJ-276D PSD plastic version for fast neutron detection and 6Li-loaded plastics for thermal neutron and antineutrino detection applications. Performance projections of the new PSD plastics indicate a likely degradation of less than 10 % over 5–10 years in comparison to previous EJ-276 that might lose up to 30–40 % of the scintillation light during 1–2 years of storage or deployment under ambient conditions.

Compact Ion Beam System for Fusion Demonstration

We demonstrate a compact ion beam device capable of accelerating H+ and D+ ions up to 75 keV energy, onto a solid target, with sufficient beam current to study fusion reactions. The ion beam system uses a microwave driven plasma source to generate ions that are accelerated to high energy with a direct current (DC) acceleration structure. The plasma source is driven by pulsed microwaves from a solid-state radiofrequency (RF) amplifier, which is impedance matched to the plasma source chamber at the S-band frequency in the range of 2.4–2.5 GHz. The plasma chamber is held at high positive DC potential and is isolated from the impedance matching structure (at ground potential) by a dielectric-filled gap. To facilitate the use of high-energy-particle detectors near the target, the plasma chamber is biased to a high positive voltage, while the target remains grounded. A target loaded with deuterium is used to study D-D fusion and a B4C or LaB6 target is used to study p-11B fusion. Detectors include solid-state charged particle detector and a scintillation fast neutron detector. The complete ion beam system can fit on a laboratory table and is a useful tool for teaching undergraduate and graduate students about the physics of fusion.

Performance of NB-CTMFD Detector Versus Ludlum 42-49B, and Fuji NSN3 Detectors for Hard (Am-Be) and Soft (Cf-252 Fission) Energy Spectra Neutron Sources Within Lead/Concrete Shielded Configurations

Abstract This paper presents the results of neutron detection efficiency and dosimetry between a nonborated centrifugally tensioned metastable fluid detector (NB-CTMFD) configured to detect fast (>0.1 MeV) versus two widely used combined thermal and fast neutron detection devices of similar form factors: moderated He-3 based Ludlum-42-49BTM neutron detector, and, the Fuji NSN3TM pressurized nitrogen-methane filled neutron detector. The one-on-one performance comparisons were conducted using hard (Am-Be) and soft (Cf-252 fission) neutron spectra isotope neutron sources positioned behind various levels of lead and concrete shielding ranging in thickness from 0 cm (unshielded) to up to 30 cm. The comparisons were conducted together with Monte Carlo N-Particle (MCNP) code simulations to account for 3-D effects and to relate the detection sensitivity with the dose rate. The MCNP model results for the neutron energy spectrum were validated versus experimental measurements using the H*TMFD. While the Ludlum and NSN3 detectors operate at a fixed sensitivity setting, the NB-CTMFD detector could be operated at various sensitivity levels by varying the tensioned metastable negative pressure (Pneg) from 0.3 MPa to 0.7 MPa. The NB-CTMFD (configured for fast: >0.1 MeV neutron detection at Pneg = 0.7 MPa) offered relative sensitivity enhancements of up to 15x greater than the Ludlum and ∼5x greater than the NSN3 detector for low shielding thicknesses. For larger thicknesses, the advantage factor for NB-CTMFD unit reduces with increased fast neutron removal via down-scattering, which benefits the Ludlum and NSN3 detectors. Our companion paper compares performance with a Cf-252 spectrum using a borated CTMFD (covering dual energy bins: thermal-epithermal and fast energy ranges) wherein, it is demonstrated that the advantage factor for the CTMFD (if borated) remains elevated at the 5–10x higher level for low and large shielding thicknesses and soft and hard neutron spectra.

Response of a high-pressure 4He scintillation detector to nuclear recoils up to 9 MeV

Helium-4-based scintillation detector technology is emerging as a strong alternative to pulse-shape discrimination-capable organic scintillators for fast neutron detection and spectroscopy, particularly in extreme gamma-ray environments. The 4He detector is intrinsically insensitive to gamma radiation, as it has a relatively low cross-section for gamma-ray interactions, and the stopping power of electrons in the 4He medium is low compared to that of 4He recoil nuclei. Consequently, gamma rays can be discriminated by simple energy deposition thresholding instead of the more complex pulse shape analysis. The energy resolution of 4He scintillation detectors has not yet been well-characterized over a broad range of energy depositions, which limits the ability to deconvolve the source spectra. In this work, an experiment was performed to characterize the response of an Arktis S670 4He detector to nuclear recoils up to 9 MeV. The 4He detector was positioned in the center of a semicircular array of organic scintillation detectors operated in coincidence. Deuterium–deuterium and deuterium–tritium neutron generators provided monoenergetic neutrons, yielding geometrically constrained nuclear recoils ranging from 0.0925 to 8.87 MeV. The detector response provides evidence for scintillation linearity beyond the previously reported energy range. The measured response was used to develop an energy resolution function applicable to this energy range for use in high-fidelity detector simulations needed by future applications.

Pulsed fast neutron yield measurements based on 79mBr activation in LaBr3(Ce)

This work aims to test the concept of an activation detector for pulsed DD fusion neutron sources, based on the production of metastable Br79m within a LaBr3(Ce) scintillator crystal via (n,n′) inelastic scattering. The pulsed neutron source employed is the NX3 Plasma Focus (PF) device operated in deuterium gas, which yields about 109 neutrons per shot. A range of D2 gas pressures, from 1 to 13 mbar are used to vary the test conditions. For the sake of comparison, a beryllium fast-neutron activation detector is used simultaneously with the LaBr3(Ce), and for each NX3 PF shot we derive neutron yield values from both Be and LaBr3(Ce) detectors, denoted YnBe and YnLaBr. The two detectors are positioned in the equatorial plane (θ=90°) of the NX3 to expose them to bursts of neutrons with energies close to 2.5 MeV, to simulate a thermonuclear DD fusion source. Overall, the shot-to-shot values of YnBe and YnLaBr obtained compare reasonably well. At each D2 gas pressures the 10-shot averaged values ⟨YnBe⟩ and ⟨YnLaBr⟩ are mostly within 10% of one another; for the worst case (10 mbar) ⟨YnLaBr⟩ is 25% higher than ⟨YnBe⟩. Overall, it is concluded that LaBr3(Ce) scintillation detectors can function as a capable and readily obtainable fast-neutron activation detector for measuring neutron yields from pulsed DD fusion sources.

HETEROSTRUCTURED SCINTILLATORS BASED ON ORGANIC SINGLE CRYSTAL GRAINS FOR A HIGH PULSE SHAPE DISCRIMINATION

This article is related to studying the properties and improving the characteristics of the new types of organic heterostructured scintillators as detectors of fast neutrons and short-range charged particles. This research is aimed to find the opportunities to improve the characteristics of the detector, based on a heterostructured scintillation material, and to expand the possibilities of its practical applications, in particular, for the tasks of separate detection of ionizing radiations of different types.

Study on scintillation properties and proton-induced radiation damage of LaCl[formula omitted] crystals

A Cs2LiYCl6 (CLYC) scintillation crystal is a promising candidate for fast neutron spectroscopy due to its dual mode gamma/neutron capability and good energy resolution. Despite promising features, CLYC’s limited radiation tolerance and inability to separate alpha/proton particles using pulse shape discrimination (PSD) method restrict its applicability in fast neutron spectroscopy. The significant cross-sections for 35Cl(n,p)35S and 35Cl(n, α)32P reactions make 35Cl-containing crystals attractive candidates for fast neutron detection, prompting their development as a promising new solution. This study reports the growth of LaCl3 crystals via the Bridgman technique, enabling further exploration of their scintillation and material properties for fast neutron detection applications. The effects of the proton irradiation on LaCl3 crystals were investigated by irradiating them with a 100 MeV proton beam at the Korea Multi-purpose Accelerator Complex. The study quantified radiation damage by comparing the pre- and post-irradiation scintillation properties and PSD of the LaCl3 crystals. The results of the measurements demonstrate that LaCl3 crystals are promising candidates for applications in fast neutron identification, spectroscopy, and space mission, maintaining performance even under high-radiation environments.

Operation of a 250μm-thick SiC detector with DT neutrons at high temperatures

The Silicon Carbide detector (SiC) is an object of research as an alternative to diamond detectors for fast neutron detection and spectrometry where harsh environments are an issue, like in Tokamaks. Since future breeding blankets mock-ups will feature temperatures up to 550 °C, diamond detectors were characterized in the past, finding limitations in their functionality at high temperatures. This paper expands on the previous work by proving the detection of fast neutrons with good detection parameters of a 250 μm-thick 4 H-SiC detector prototype at temperatures up to 250 °C, highlighting the detector's excellent resilience to temperature. The experiment is conducted with instrumentation similar to the one used in the past with diamond detectors, using as source of irradiation the Frascati Neutron Generator (FNG) in ENEA, which is accelerator driven neutron source based on deuterium-tritium (DT) fusion reaction.

Vaporized purification and growth of optically transparent Trans-Stilbene for fast neutron detection applications

The paper reports the successful growth of large, crack-free trans-stilbene (TSB) single crystals using an in-house developed vertical Bridgman setup. The material purification involved a novel vaporized method at 130 °C. Parameters like furnace setup and ampoule’s cone angle were optimized during the growth process. The Powder XRD pattern confirms the phase of material and crystallinity. The crystal exhibited high transmittance (78 %) in the visible region, with an optical band gap of 3.4 eV. Photoluminescence study indicated strong blue emission at 380 nm, with radioluminescence spectroscopy showing emissions at 387 nm under X-ray radiation. The crystal exhibited a scintillation decay time of 6 ns under 137Cs gamma source, highlighting its fast decay and efficient PSD property with a figure of merit of 2.24 for fast neutron detection applications.

Neutron detection in mixed short-pulsed fields with intense photon flashes for LINAC-based active interrogation applications

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.

Testing of an organic metal halide perovskite for fast neutron detection

In this work, we synthesized and characterized the Methylhydrazinium Lead Trichloride MHyPbCl3(CH3NH2NH2PbCl3) perovskite as a fast neutron detector. The high hydrogen density of MHyPbCl3 enables efficient energy conversion from a fast neutron into a recoiled proton through the 1H(n,n)1H elastic scattering interaction, thereby, allowing for direct charge detection. Through IV characterization and X-Ray excitation, the crystal demonstrated a high resistivity at 4.43E11Ωcm and a good mobility-lifetime product (μτ) of 9.1E-3 cm2V, respectively, under C60/BCP/Cu and Au contact configuration to form an ohmic-ohmic detector. The crystal showed a good sensitivity to X-rays using an x-ray tube. The feasibility of the direct neutron conversion detector is demonstrated using the fast neutron beam at a Research Reactor. Waveforms from a charge-sensitive pre-amplifier showed distinct radiation-induced pulses from the MHyPbCl3 detector in response to the reactor neutron beam. Using a thermal neutron filter and gamma shielding in the beam, we showed that the pulses produced were more likely from neutron interactions, despite the Pb containing MHyPbCl3 is also sensitive to gamma-rays. With those fast neutron pulses, a post-pulse processing code was used to conduct pulse height analysis (PHA) and reconstruct an energy spectrum.

Pure CaF2 crystal for fast neutron detection

Pure CaF2 crystals have been widely used for optical functional crystals due to their good optical properties, mechanical properties, and chemical stability. This study discovered the crystal's pulse shape discrimination (PSD), proving it a promising scintillator for fast neutron detection via the 40Ca neutron capture reaction. Luminescence emission spectra were studied by X-ray luminescence measurements. The maximum emission peak was observed between 250 and 300 nm, corresponding to self-trap exciton emission. The crystal response to gamma, alpha, and neutron were studied under 137Cs, 241Am, and 252Cf radiation sources, respectively. The difference in gamma and alpha decay times enabled the PSD capability of pure CaF2. Large neutron reaction cross-sections, PSD capability, and good chemical stability make pure CaF2 crystal candidates for fast neutron beam monitoring detectors. Moreover, the crystal can be used for 40Ca(n,p)40K and 40Ca(n,α)37Ag neutron capture cross-section study.

Design and performance evaluation of a compact thermal and fast neutron spectrometer

Measurement of the space neutron radiation environment has put forward new requirements for the miniaturization and lightweight design of neutron spectrometers. In this paper, a compact broad-spectrum neutron spectrometer was designed, in which the fast neutron detector was based on the EJ-254 scintillator-coupled with SiPMs array, and the thermal and epithermal neutron detectors were based on the NaI(Tl + Li) (NaIL) scintillator coupled with SiPMs array encapsulated in Al and Cd shells, respectively. The overall weight of the neutron spectrometer was only 2.4 kg, and its dimensions were 154 mm × 123 mm × 115 mm. The fast neutron energy spectrum was obtained based on the capture-gated method and the Maximum Likelihood Expectation Maximization (MLEM) unfolding algorithm; the counts of thermal and epithermal neutrons were obtained based on the optimized frequency-domain Pulse Shape Discrimination (PSD) method and cadmium difference method. The proposed neutron spectrometer with all applied methods was tested as a whole system with a252Cf and a241Am–Be source. The spectrum result was compared to an ISO standard source. The accuracy of fast part of 0.5–10 MeV was 5.9% in definition of Relative Root Mean Squared Error (RRMSE). The thermal and epithermal neutron counts were far higher than standard spectrum, and we proved it being effected by laboratory introduced neutron scattering through a simulation, thus the thermal and epithermal flux measurements was believed to be decent. The Figure of Merit (FoM) of the NaIL's PSD neutron gamma discrimination were 2.57 and 2.90 respectively.

Response of LaBr2.85Cl0.15:Ce, LaBr[formula omitted]:Ce and NaI:Tl crystals to fast and thermal neutrons

This communication reports the measurement of direct response for fast and thermal neutrons of a newly marketed scintillation crystal LaBr2.85Cl0.15:Ce, along with the widely used LaBr3:Ce and NaI:Tl crystals. It continues our investigation on the possible utility of LaBr2.85Cl0.15:Ce crystal for the detection of high-energy γ-rays and neutrons. This is the first report of the neutron response of the LaBr2.85Cl0.15:Ce crystal. The neutron response was measured for the three detectors using a calibrated Am-Be source, which emits both neutrons and γ-rays. To eliminate the events due to the interaction of the 4.4 MeV γ-ray emitted from Am-Be, the γ-ray response of all three crystals was simulated using the Monte Carlo simulation toolkit GEANT4. Events due to 2.22 MeV γ-ray produced by the capture of thermal neutrons in the paraffin moderator were also eliminated with the aid of simulations. In addition, the response due to fast neutrons was also simulated using GEANT4 and compared with the measured spectrum. This is the first report of the simulation of fast neutron response of LaBr2.85Cl0.15:Ce using GEANT4. The fast neutron detection efficiency of the three detectors has been obtained from the measured spectra.

Riptide: a proton-recoil track imaging detector for fast neutrons

Riptide is a detector concept aiming to track fast neutrons. It is based on neutron-proton elastic collisions inside a plastic scintillator, where the neutron momentum can be measured by imaging the scintillation light. More specifically, by stereoscopically imaging the recoil proton tracks, the proposed apparatus provides neutron spectrometry capability and enable the online analysis of the specific energy loss along the track. In principle, the spatial and topological event reconstruction enables particle discrimination, which is a crucial property for neutron detectors. In this contribution, we report the advances on the Riptide detector concept. In particular, we have developed a Geant4 optical simulation to demonstrate the possibility of reconstructing with sufficient precision the tracks and the vertices of neutron interactions inside a plastic scintillator. To realistically model the optics of the scintillation detector, mono-energetic protons were generated inside a 6 × 6 × 6 cm3 cubic BC-408 scintillator, and the produced optical photons were propagated and then recorded on a scoring plane corresponding to the surfaces of the cube. The photons were then transported through an optical system to a 2 × 2 cm2 photo sensitive area with 1 Megapixel. Moreover, we have developed two different analysis procedures to reconstruct 3D tracks: one based on data fitting and one on Principal Component Analysis. The main results of this study will be presented with a particular focus on the role of the optical system and the attainable spatial and energy resolution.

An investigation of the simulation response of GEM-based detector for the fast neutrons by employment of GEANT4 & MCNP MC codes

The current work explores the potential ability to identify fast neutrons with one Gas Electron multiplier (GEM) detector connected to a polyethylene (PE) converter. Hence, a simulation was tested utilizing the GEANT4 Monte Carlo and MCNP simulation codes. The GEM detector functions by detecting the charged particles generated by an (n, p) reaction on a polyethylene. Fast neutrons in the ranging with energy levels of 1.0 MeV to to 25 MeV have the ability to travel towards the detector surface and evaluation was conducted from its response. For the 1 mm, 2 mm and 3 mm converter thickness, the sensitivity remains ∼ 9.8% and 13.4%, and 14.2% respectively via GEANT4 QGSP_BERT_HP physics lists. For the same converter thicknesses, sensitivity remains ∼ 9% and 12%, and 12.5% using the QGSP_BIC_HP physics list. Using the MCNP, with a 1 mm, 2 mm and 3 mm converter thickness, the sensitivity remains ∼ 12.8%, 13.3% and 13.6% via cell-flux tally method, while with the MCNP pulse- height technique with the same converter thicknesses, the sensitivity remains ∼ 10.6%, 12% and 13.3% respectively. The current findings reveals that GEM detector exhibits a clear and efficient response to inserted fast neutrons. Consequently, GEM based detectors have a potential to be a better candidate for fast neutron detection.

GENESIS: Gamma Energy Neutron Energy Spectrometer for Inelastic Scattering

Improved neutron inelastic scattering cross section data are needed to inform integral benchmark studies and advance applications in a wide variety of areas including nuclear energy, stockpile stewardship, nonproliferation, and space exploration. Neutron inelastic scattering also serves as a non-selective probe of low-lying nuclear structure. To help meet these needs, the Gamma Energy Neutron Energy Spectrometer for Inelastic Scattering (GENESIS) was constructed at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. This array couples high-resolution γ-ray detectors and fast neutron detectors to achieve single and coincident n/γ detection over a broad energy range. The current configuration of the array includes 26 organic liquid scintillators and four high-purity germanium detectors (two single-crystal and two four-crystal CLOVER detectors with two-fold segmentation). The array was constructed with minimal supporting material and designed to cover a wide range of secondary particle angles and energies with limited inter-element scattering. Data acquisition is accomplished using Mesytec MDPP-16 multi-channel high-resolution digital pulse processing modules. The array characteristics, including γ-ray and neutron energy resolution, timing resolution, and detection efficiency were measured and used to validate a Geant4 model of the array. The primary sources of neutron background and the uncertainties in the determination of incident and secondary neutron energy were assessed. GENESIS provides a new capability to address nuclear data needs and facilitates the advancement of a wide range of nuclear applications.

Determination of fission barrier height of Fr210 and Ra210 via neutron measurement

Fission barrier heights of short-lived nuclei away from line of β stability are not known reliably. Low-energy fission of Fr210 and Ra210, produced by (d,p) and (d,n) transfer reaction on the re-accelerated unstable beam Fr209 was investigated at HIE-ISOLDE. Four Timepix3 pixel detectors were installed on the body of the ACTAR TPC demonstrator chamber. Polyethylene converters were used for the detection of fast neutrons. Since no significant background was observed, it was possible to measure the spatial distribution of emitted neutrons reflecting the fission excitation function. Subsequent simulations employing the results of the code and available data on fission fragment distributions allowed to estimate directly the value of the fission barrier height for the neutron-deficient nucleus Fr210. This first direct measurement confirmed the reduction of the fission barrier compared to available theoretical calculations by 15–30%. Published by the American Physical Society 2024