Neutron Detection Efficiency Research Articles

Thermal neutron measurement by single crystal CVD diamond detector applied with the pulse shape discrimination during deuterium plasma experiment in LHD

Abstract The Pulse shape discrimination (PSD) technique for single crystal CVD diamond detector (SDD) was applied to the real-time thermal neutron measurement during the 3rd campaign of Deuterium-Deuterium (D-D) plasma experiment in the Large Helical Device (LHD). The PSD method is based upon the different shape of electrical pulses produced in diamond by gamma-ray (triangular-shaped pulse) and energetic ions (rectangular-shaped pulse), respectively. An improved PSD was developed which makes use of the full width at half maximum (FWHM) and the full width at 2/3 of the peak height (FW2/3 PH). These two parameters reflect the difference in the pulse shape produced by gamma-rays and energetic ions. The performance of this improved PSD technique was first tested irradiating the SDD by gamma-rays from 60Co and alphas from 241Am radiation sources, respectively. Then, using a 6LiF thermal neutron converter, a successful discrimination between gamma-rays and alpha particles and tritons generated by the 6Li(n,α)3H reaction induced by neutrons from 252Cf spontaneous fission neutron source was achieved. Thanks to this PSD processing technique, the thermal neutron detection efficiency increased about 1.7 times compared to previous measurements performed without the PSD technique. The real-time thermal neutron measurement by SDD with this enhanced PSD processing was also used during D-D plasma discharges in the Large Helical Device (LHD). It was found that both the time integrated counts and the time evolution count rate measured by the SDD reproduced well that of the fission chamber used as official LHD neutron monitor. The capability of the SDD detector using the PSD technique of precise real-time thermal neutron measurement in LHD was demonstrated.

A Plutonium Mass Uncertainty Assessment Using a Cherenkov-Based Neutron Multiplicity Water Detector

We present a new analysis of the sensitivity of a water Cherenkov-based neutron multiplicity counter for nondestructive assay of trace quantities of 240Pu. The multiplicity counter [water-based neutron detector (WaND)] contains 1.0 m3 of water doped with 0.2% gadolinium in the form of a gadolinium salt (0.4% GdCl3). It can be used for testing the presence of trace quantities of 240Pu within a sample of unknown material by observing the correlated timing behavior of neutron capture candidates in the detector. The new analysis takes advantage of the fact that the detector is comprised almost entirely of a homogeneous medium, which permits the use of a simple model to reproduce the observed neutron capture timing behavior. The results of this analysis indicate that the detector has an absolute neutron detection efficiency of 23.4 ± 1.1% and is sensitive to a 240Pu mass as small as 2.3 mg (at $1\sigma $ ) after a 1-h data acquisition.

Thermal Neutron Discrimination Using a Novel Phoswich Detector of Gd3Ga3Al2O12:Ce,B and CsI:Tl Single Crystals

A phoswich detector was fabricated using a combination of single-crystal scintillators of CsI:Tl and Gd3Ga3Al2O12:Ce,B. The performance characteristics of this novel phoswich detector were investigated for thermal neutron detection in the presence of different gamma backgrounds using an Am–Be source and in a research reactor beam line. High atomic density and excellent thermal neutron capture cross section of Gd leads to the high detection efficiency for thermal neutrons in a 1-mm thin disk of Gd3Ga3Al2O12 crystal. The high figure of merit of ~6.5 obtained for thermal neutron detection ensures the detector’s excellent discrimination property in the presence of high gamma background.

The research of laser-based rapid measurement system for scintillator neutron detectors arrays

Scintillator Neutron Detectors Arrays (SNDA) were successfully installed at General Purpose Powder Diffractometer (GPPD) at the China Spallation Neutron Source (CSNS). The inhomogeneity of the detection efficiency in each detector module, which caused by the gain nonuniformity of the multi-anode photo-multiplier tubes (MA-PMTs) and the inconsistency of the wave-length shifting fibers in collecting scintillation photons, need to be mitigated before the installation. An automated rapid measurement system based on the blue laser and the two-dimensional mobile platform was developed to calibrate the light response of each channel in detector modules. According to the test results of this system, the electronics threshold of each channel of the SNDA is adjusted. Before the installation of the all 40 SNDA modules in GPPD, the electronics thresholds of each channel are adjusted according to the measurement results of this rapid measurement system. Compared with the unadjusted detector module, the adjusted one obtained a better uniformity of the neutron detection efficiency. The inhomogeneity of the detection efficiency is improved from 27.4% to 10.9%. The test result of the diffraction peak of the standard sample Si showed that the adjusted SNDA works well in GPPD.

A Gadolinium Metal-Organic Framework Film as a Converter Layer for Neutron Detection.

Metal-organic frameworks (MOFs) are known for their versatility in terms of their crystalline structure, porosity, resistance to temperature, radiation damage, and luminescence among others. Gadolinium (Gd) is one of the elements with the highest reported cross-section for low energy neutron capture, producing internal conversion electrons and γ rays as a result of the neutron absorption. The development of Gd-BTC films (BTC=1,3,5-benzenetricarboxylate) is shown that were deposited on Si and Al substrates by airbrushing, and characterized by profilometry, Raman, EDX and X-ray diffraction. Radiation damage, thermal decomposition and neutron absorption of these films were studied as well. Gd-BTC films were attached to CMOS devices (Complementary Metal-Oxide-Semiconductor), which are sensible to the internal conversion electrons, in order to build a neutron detector. The devices Gd-BTC/CMOS could selectively detect neutrons in the presence of γ rays with a thermal neutron detection efficiency of 3.3±0.1 %, a signal to noise ratio of 6 : 1, and were suitable to obtain images.

Optimization and characterization of a silicon photomultiplier-based ZnS(Ag) proton recoil fast neutron detector for nuclear fuel performance monitoring at TREAT

The restart of the Transient Reactor Test Facility (TREAT) at Idaho National Laboratory and consequent refurbishment of the Fuel Motion Monitoring System (FMMS), or Hodoscope, offers the opportunity to upgrade the detector system used for neutron imaging. Silicon photomultipliers (SiPMs) are a viable option for updating the Hodoscope to yield improved fuel monitoring capability. The Hodoscope uses ZnS(Ag) proton recoil scintillators (PRS) that provide good gamma-ray suppression and discrimination. Previous work showed that the Hamamatsu S13360-6075CS SiPM offers the best neutron detection and gamma-ray discrimination capability with the ZnS PRS. This work optimizes a SiPM-based detector and develops a PRS prototype for testing. Specifically, possible overvoltages for use are determined by confirming steady operation over extended measurement times. In addition, various SiPM-circuit implementations are tested to optimize the detector according to desired properties, and ultimately a PRS prototype is developed with modifiable components for versatile testing. Measurements of the neutron detection efficiency and gamma-ray rejection efficiency of SiPM-based PRS detectors and a reference PMT-based detector are also carried out. Neutron detection efficiency ranges between 1–2%, and detected gamma-ray rejection efficiency is on the order of 10−7. Use of a low-pass filter only or a low-pass filter and 50-ω shunt resistor is recommended for the SiPM-based detector, and both configurations demonstrate improved performance over the PMT-based detector.

Position-dependent neutron detection efficiency loss in 3He gas proportional counters

The position-dependent neutron detection response of a 3He gas proportional counter (GPC) was characterized using a collimated (3-mm-wide), monoenergetic (0.05 eV) neutron beam. For neutrons incident on the GPC near the ends of the active region, the neutron capture peak broadens and the position shifts to lower pulse-height channels. This “edge effect” is due to lower gas gain within the decreasing electric field near the end of the active volume. For simple peak-region-summing analyses, the consequence is a loss of events that is equivalent to a 13% reduction in the active area of our GPC. Summing over all events above the triton wall-effect feature significantly reduces this efficiency loss. Whole-sensor illumination measurements simulated with Geant4 required a correction for the edge effect to accurately reproduce the shape and amplitude of the measurements. Once these corrections were applied, the Geant4 models reproduce the whole-sensor count rates to within 10%.

ABSOLUTE MEASUREMENT OF 14.57MeV NEUTRON FLUENCE RATE USING PROTON RECOIL NEUTRON TELESCOPE.

A single stage vacuum-type proton recoil neutron telescope (PRT) was used for accurate measurement of 14.57MeV neutron fluence rate from an indigenously developed D-T neutron generator at Purnima, BARC. The telescope consists of a polyethylene radiator having 4cm diameter and CsI (Tl) scintillation crystal having thickness 1.5mm and 4cm diameter separated by 20.5cm kept in a vacuum chamber. The neutron detection efficiency of the telescope for 14.57 MeV neutrons was calculated analytically using n-p scattering cross section data from Evaluated Nuclear Data File VII and also evaluated using fluka simulation. The relativistic transformation of n-p differential scattering cross section from centre-of-mass to laboratory system was used for calculating the efficiency of PRT. The 14.57 MeV neutron fluence rate was also measured using copper foils. The comparison of fluence rate measured using PRT and copper foil activation techniques is presented in this paper. The total uncertainty in measurement using PRT and copper foil activation technique is found to be 3.93 and 6.97%, respectively.

Simulation of charge drift in surface doped, pixelated micro-structured semiconductor neutron detectors

A semiconductor neutron imaging device is proposed (X-MSND) based on high efficiency, Micro-structured Semiconductor Neutron Detector (MSNDs) bump bonded onto a Timepix pixelated readout chip. The device serves as a combined neutron and photon imager with a 256x256 pixel array, using per-pixel time-over-threshold (ToT) energy deposition. A method of simulation was developed by combining finite-element tools (COMSOL), particle transport code (Geant4), and charge transport code (Allpix2), to model the time-dependent charge induction on pixel electrodes to be read-out by the Timepix. Pixel cluster events have been simulated as a result of incident neutron irradiation for the X-MSND and compared to a planar coated diode device. The X-MSND design produced thermal neutron detection efficiency of 14%, significantly greater than the theoretical maximum for planar devices. Simulated pixel clusters showed similar qualitative characteristics as planar neutron sensitive Timepix hybrid detectors.

Characterization of a real-time neutron detector for boron neutron capture therapy using a thin silicon diode

A real-time neutron detector was developed to measure an intense neutron beam, based on both a thin silicon sensor and an extremely thin neutron converter for boron neutron capture therapy (BNCT). Neutron response function and detection efficiency were evaluated at the BNCT facility. The response function consists of neutron events, detecting both triton particles produced from the 6Li (n,t)4He reaction and alpha particles from the 10B (n,α)7Li reaction. The detector is able to clearly separate the BNCT neutron beam from coexisted gamma rays. A depth distribution of slow neutron flux in an acrylic block was experimentally obtained. While the relative depth distribution of over 20 mm in depth is in line with the results of the neutron activation measurements of gold, the absolute values are around 17% smaller than the corresponding neutron activation results, which was due to the incomplete evaluation of the neutron detection efficiency and angular-dependent response of the neutron detector.

Measurement of neutron-proton capture in the SNO+ water phase

The SNO+ experiment collected data as a low-threshold water Cherenkov detector from September 2017 to July 2019. Measurements of the 2.2-MeV $\gamma$ produced by neutron capture on hydrogen have been made using an Am-Be calibration source, for which a large fraction of emitted neutrons are produced simultaneously with a 4.4-MeV $\gamma$. Analysis of the delayed coincidence between the 4.4-MeV $\gamma$ and the 2.2-MeV capture $\gamma$ revealed a neutron detection efficiency that is centered around 50% and varies at the level of 1% across the inner region of the detector, which to our knowledge is the highest efficiency achieved among pure water Cherenkov detectors. In addition, the neutron capture time constant was measured and converted to a thermal neutron-proton capture cross section of $336.3^{+1.2}_{-1.5}$ mb.

Fabrication and performance evaluation of GaN thermal neutron detectors with 6LiF conversion layer**Project supported by the National Natural Science Foundation of China (Grant Nos. 61964001 and 61961001), the State Key Laboratory of Particle Detection and Electronics (Grant No. SKLPDE-KF-2019), the Natural Science Foundation of Jiangxi Province, China (Grant Nos. 20192BAB207033 and 20181BAB202026), the Foundation of State Key Laboratory Breeding Base

A GaN-based pin neutron detector with a 6LiF conversion layer was fabricated, and can be used to detect thermal neutrons. Measurement of the electrical characteristic of the GaN-based pin neutron detector showed that the reverse leakage current of the neutron detector was reduced significantly after deposition of a 6LiF conversion layer on the detector surface. The thermal neutrons used in this experiment were obtained from an 241Am–Be fast neutron source after being moderated by 100-mm-thick high-density polyethylene. The experimental results show that the detector with 16.9-μm thick 6LiF achieved a maximum neutron detection efficiency of 1.9% at a reverse bias of 0 V, which is less than the theoretical detection efficiency of 4.1% calculated for our GaN neutron detectors.

Neutron Detection Using a Gadolinium-Cathode Gas Electron Multiplier Detector

A gas electron multiplier (GEM) detector with a gadolinium cathode has been developed to explore its potential application as a neutron detector. It consists of three standard-sized ($10\times 10$ cm${}^{2}$) GEM foils and a thin gadolinium plate as the cathode, which is used as a neutron converter. The neutron detection efficiencies were measured for two different cathode setups and for two different drift gaps. The thermal neutron source at the Korea Research Institute of Standards and Science (KRISS) was used to measure the neutron detection efficiency. Based on the neutron flux measured by KRISS, the neutron detection efficiency of our gadolinium GEM detector was $4.630 \pm 0.034(stat.) \pm 0.279(syst.) \%$.

Measurement of the detection efficiency response curve of stilbene detectors based on a Back-n white neutron source at the CSNS

The time-of-flight (TOF) of an associated white neutron beam line exploiting back-streaming neutrons (Back-n) at China Spallation Neutron Source (CSNS) was obtained using a scintillator detector consisting of stilbene crystal, a photomultiplier tube (PMT), a screening can, and a high sampling rate oscilloscope. An original energy-count spectrum was acquired based on the time-of-flight method. Four kind of stilbene crystals were placed at different angles and distances from the polyethylene scattering target, with different sizes of Φ15 mm × 5 mm, Φ25 mm × 10 mm, Φ50 mm × 10 mm and Φ50 mm × 30 mm. The detection efficiency of multiple energy points was calculated based on the reference energy spectrum, and 10 detection efficiency response curves between 0.5 MeV and 20 MeV were obtained in accordance with a Monte Carlo simulation. The results demonstrated the feasibility of using a scintillator detector for neutron detection efficiency at a white neutron source. This method shows great potential in neutron detection efficiency calibration for all organic scintillation detectors.

Characterization of boron-coated silicon sensors for thermal neutron detection

Silicon neutron detectors can operate at low voltage and come with ease of fabrication and the possibility of integration of readout electronics and thus are attractive from an application point of view. In this paper, we have studied thermal neutron capture by silicon diodes coated with boron carbide (B4C). One of the surfaces of the diodes was covered with either natural B4C (natB4C) or with enriched B4C (enB4C). We have investigated: (a) the effect of increase in the sensitive area of the surface of the diode covered with B4C on the neutron detection efficiency and (b) the effect of enrichment of 10B in B4C. The difference in 10B in natB4C (16 at.% in the deposited film) and enB4C ( 79 at.% in the deposited film) leads to about three times increase in detection efficiency of the same detector. For the given experimental conditions, we do not observe a direct relationship between increase in the surface area and the detection efficiency. Energy spectra obtained by Geant4 simulations support the experimental observation of finding no direct relation between increase in the surface area and the detection efficiency.

Performance Assessment of Amplification and Discrimination Electronic Devices for Passive Neutron Measurements

The assessment of fissile material mass is a key requirement to enhance radioactive waste management and to ensure a high level of safety in the nuclear industry. The assessment of plutonium fissile mass by passive coincidence measurements is usually obtained by detecting the neutrons generated by the spontaneous fissions of Pu isotopes. The detection and the quantification of a fissile mass in the radioactive waste can also be carried out using active neutron interrogation with a pulsed D-T neutron generator. The 14-MeV neutrons are moderated to induce fissions in the uranium and plutonium-contaminated waste. The emitted neutron signal can be analyzed by considering their detection time after the generator pulse. Data are measured according to the principles of the neutron measurement techniques. As proportional counters filled with 3He gas display high neutron detection efficiency and good gamma-ray immunity, they are the reference detector for passive neutron coincidence counting. A charge preamplifier or a current amplifier, depending on applications, collects the electric pulse produced by neutron interaction in the 3He gas, and a threshold discriminator produces a logic pulse used for neutron counting. This article describes the performance assessment of different commercially-available electronics from Mirion Technologies, Precision Data Technology (PDT), Mesytec, as well as MONACO electronics originally developed by CEA LIST for fission chamber measurements in experimental reactors. Comparative passive neutron measurements are carried out with these electronics at CEA/DEN Nuclear Measurement Laboratory in Cadarache. Overall, PDT and Mesytec electronics show similar detection efficiency as the ACH-NA98 charge amplifier, which is commonly used in our laboratory for such applications. However, MONACO electronics have a lower detection efficiency, similar to the Mirion 7820 current amplifier used in specific high-count rate applications. An optimization of MONACO settings would probably be necessary to adapt to 3He counters instead of fission chambers.

Simulation-based optimization of a multilayer 10B-RPC thermal neutron detector

A Monte Carlo simulation-based optimization of a multilayer 10B-RPC thermal neutron detector is performed targeting an increase in the counting rate capability while maintaining high ({\ extgreater}50%) detection efficiency for thermal neutrons. The converter layer thicknesses of individual RPCs are optimized for several configurations of a detector containing a stack of 10 double gap RPCs. The results suggest that it is possible to reach a counting rate which is by a factor of eight higher in comparison to the rate of a detector with only one double-gap RPC. The effect of neutron scattering inside the detector contributing to the background is analyzed and design modifications of the first detector prototype, tested at neutron beam, are suggested.

Development of new trigger system for KamLAND2-Zen

KamLAND2-Zen is the future plan for the existing KamLND-Zen experiment, which will search for neutrinoless double-beta decay. In this experiment, muon spallation products are expected to be the main background. Spallation backgrounds can be tagged by delayed coincidence with neutrons emitted in spallation. Therefore, it is important to detect neutrons with high efficiency. However, enhancement of light yield will increase after-pulses and fake triggers due to them resulting in DAQ deadtime and low detection efficiency of neutrons. To solve this problem, a new trigger scheme which uses simultaneous hit of neighboring PMTs was developed. According to a simulation performed with real PMT waveforms, this scheme is expected to improve neutron detection efficiency from 54% to 89%. Consequently 99% of 10C background events can be tagged.

Direct thermal neutron detection by the 2D semiconductor 6LiInP2Se6.

Highly efficient neutron detectors are critical in many sectors, including national security1,2, medicine3, crystallography4 and astronomy5. The main neutron detection technologies currently used involve 3He-gas-filled proportional counters6 and light scintillators7 for thermalized neutrons. Semiconductors could provide the next generation of neutron detectors because their advantages could make them competitive with or superior to existing detectors. In particular, solids with a high concentration of high-neutron-capture nuclides (such as 6Li, 10B) could be used to develop smaller detectors with high intrinsic efficiencies. However, no promising materials have been reported so far for the construction of direct-conversion semiconductor detectors. Here we report on the semiconductor LiInP2Se6 and demonstrate its potential as a candidate material for the direct detection of thermal neutrons at room temperature. This compound has a good thermal-neutron-capture cross-section, a suitable bandgap (2.06 electronvolts) and a favourable electronic band structure for efficient electron charge transport. We used α particles from an 241Am source as a proxy for the neutron-capture reaction and determined that the compact two-dimensional (2D) LiInP2Se6 detectors resolved the full-energy peak with an energy resolution of 13.9 per cent. Direct neutron detection from a moderated Pu-Be source was achieved using 6Li-enriched (95 per cent) LiInP2Se6 detectors with full-peak resolution. We anticipate that these results will spark interest in this field and enable the replacement of 3He counters by semiconductor-based neutron detectors.

Counting Efficiency and Neutron/Gamma Ratio for KDP: Tl+ and UPS-923A Scintillators in a Single Photone Detection Mode

This research related to registration of the fast neutrons with a detector based on the inorganic KDP: TL+ mono crystal (KH2PO4 potassium dihydrogen phosphate) and plastic UPS-923A. The crystal of the KDP: TL+ detector grown from a water solution by the method of lowering the temperature. The high concentration of hydrogen nuclei in the KDP: TL+ crystal grid makes it possible to detect neutron radiation with an efficiency comparable to polystyrene scintillators. KDP: TL+ crystals have a high radiation resistance (up to 1010 neutrons/cm2), which significantly expands the spectrum of their application in high-energy physics applications, intense neutron fields. In this work, we used a technique for recording the detector response in the photon counting mode and pulse filtering mode. Since the detector operates on the principle of detecting gamma quanta from the reactions (n, n 'γ), (n, n' γ)res, (n, γ)cap and others, this makes it possible (in a filtering mode) to isolate the mechanisms of cascade generation processes in the volume of the detector caused by secondary gamma quanta from excited states of compound nuclei. The gamma quanta of the elastic scattering reaction (n, n' γ) for the KDP: TL+ scintillator nuclei are the start of the cascade process of the discharge of excited isomeric states of the input, intermediate, and final nuclei. Measurements of the detection efficiency of fast neutrons were carried out with a KDP: TL+ crystal of size 18x18x42 mm in spherical geometry. The obtained detector reviews in units of impulse / particle for sources and 239Pu-Be and 137Cs were 3.57 and 1.44. In this case, a broadband path with a speed of 7 ns was used. In addition, the counting efficiency of the narrow-band tract measured simultaneously with a processing time of 1 μs and 6.4 μs. The received response from the KDP: TL+ detector (in units of impulse/particle) for both sources 239Pu-Be and 137Cs was 0.09 and 0.00029. The n/γ ratio coefficient was 310. The given measurements of a polystyrene-based scintillator size of 40×40×40 mm. The received response in a single photon-counting mode from the plastic detector (in units of impulse/particle) for both sources 239Pu-Be and 137Cs was 19.4 and 3.9. The n/γ ratio coefficients for detectors are also given: KDP: TL+ - 2.47 and UPS-923A - 4.97 in the 7 ns mode. The statistical error in measurements of the neutron detection efficiency was about ~ 5%.