Position-sensitive Neutron Detector Research Articles

In-beam test results of an RPC-based module for position-sensitive neutron detectors with timing readout

Recently we have proposed a new concept of a thermal neutron detector based on resistive plate chambers and 10B4C solid neutron converters, enabling to readout with high resolution in both the 3D position of neutron capture and the neutron time of flight (ToF). In this paper, we report the results of the first beam tests conducted with a new neutron RPC detection module, coupled to the position readout units of a new design. The main focus is on the measurements of the neutron ToF and identification of the converter layer where the neutron is captured, giving the position along the beam direction.

An 8-channel low power ASIC for Helium-3 tube position sensitive neutron detectors

The majority of neutron spectrometers designated for use in the China Spallation Neutron Source (CSNS) rely on position-sensitive detectors that utilize Helium-3 tube detector technology. To minimize the impact of air on neutron scattering experiments, detectors must be located inside a vacuum chamber. For these types of spectrometers, it is also advisable to house the readout electronics within the vacuum chamber to limit the number of feed-through cables required and enhance the signal-to-noise ratio. This paper proposes an application-specific integrated circuit (ASIC) dedicated to position-sensitive Helium-3 tube detectors, including front-end amplification, shaping module and readout driving buffer. The 8-channel chip, named HEROCV1 (HElium-3 ReadOut Circuits), achieves an input dynamic range from 10 fC to 1 pC, with a counting rate of up to 100 kHz. The equivalent noise charge (ENC) measurement is 1297e-@15pF, and the power consumption is less than 9.9 mW per channel. The ASIC has replaced the traditional front-end circuit based on discrete components, fundamentally addressing the issue of front-end power consumption and enabling the entire detector system to operate in a vacuum environment.

Position sensitive ZnO:Zn neutron detector – A high count rate alternative to ZnS:Ag scintillation detectors

ZnO:Zn is a low afterglow scintillator that is investigated here as a possible higher count rate alternative to ZnS:Ag for scintillation neutron detectors at scattering facilities. In the present work the first position sensitive neutron detector using ZnO:Zn has been produced and its detector performance is evaluated in comparison to a typical ZnS:Ag detector. The detection efficiency of the ZnO:Zn detector at 1 Å was measured to be 74% that of the ZnS:Ag detector, due to lower light output and collection in the ZnO:Zn detector. The trigger efficiency of the ZnO:Zn detector was 61% with gamma sensitivities on the order of 10−5; in comparison, the ZnS:Ag detector was able to achieve trigger efficiencies of 94% at gamma sensitivities ∼10−6. Areas of development to improve these limitations will be discussed. Most importantly, the rate capability of the ZnO:Zn detector was demonstrated to be approximately two times higher than the current standard ZnS:Ag scintillation detectors. With optimisation of signal processing parameters a factor of six times improvement in rate capability may be possible, indicating potential for the use of ZnO:Zn detectors in higher count rate applications.

A Novel, Low-Cost, Position-Sensitive Neutron Detector to Support Thick-Target Inverse Kinematics Experiments for Nuclear Data Measurements

High quality nuclear data lie at the heart of accurately modelling stellar systems and terrestrial nuclear reactors. However, some key reaction cross sections have large uncertainties, which limit such models in predicting isotopic abundances and other aspects of stellar evolution, along with key operational parameters for nuclear reactors. Reactions involving neutrons are particularly difficult to measure experimentally in laboratories, not least due to the unique challenges involved when detecting neutrons. We present a new approach to measuring nuclear reactions involving neutrons by exploiting the Thick-Target Inverse Kinematics (TTIK) approach. For such measurements, a new detector called ATTIKUS (A Thick-Target Inverse Kinematics detector by Universities in Sheffield) is under construction. Here we present designs and Geant4 Monte-Carlo simulations of the detector. The simulations indicate that a neutron position reconstruction resolution of 10 cm is obtainable and demonstrate how this device could be applied to the 13C(α,n) reaction, which is considered to be the main neutron source for the s-process in low-mass Asymptotic Giant Branch stars. In the TTIK method, the emission position of the neutron (the nuclear interaction position in a gaseous target) is directly linked to the centre-of-mass energy of the reaction. Therefore, a position resolution will translate into an energy resolution, depending on the beam-target combination. The inverse reaction, 16O(n,α), causes a large uncertainty in calculating the effective neutron multiplication factor, Keff in nuclear reactors, so improvements are required here.

Performance optimization of the scintillator neutron detectors for EMD in CSNS

Abstract Chinese Spallation Neutron Source (CSNS) has successfully produced its first neutron beam in 28th August 2017. It has been running steadily from March, 2018. According to the construction plan, the Engineering Materials diffractometer (EMD) will be installed between 2019- 2023. This instrument requires the neutron detectors with the cover area near 3m2 in two 90° neutron diffraction angle position, the neutron detect efficiency better than 40%@1Å, and the spatial resolution better than 4mm×200mm in horizontal and vertical directions respectively. We have developed an one-dimensional position sensitive neutron detector based on the oblique 6LiF/ZnS(Ag) scintillators, wavelength shifting fibers and SiPMs (Silicon Photomultipliers) readout. The inhomogeneity of the neutron detection efficiency between each pixel and each detector module, which caused by the inconsistency of the wave-length shifting fibers in collecting scintillation photons, need to be mitigated before the installation. A performance optimization experiment of the detector modules was carried out on the BL20 (Beam Line 20) of CSNS. Using water sample, the neutron beam with Φ5mm exit hole was dispersed relate evenly into the forward space. According to the neutron counts of each pixel of the detector module, the readout electronics threshold of each pixel is adjusted. Compared with the unadjusted detector module, the inhomogeneity of the detection efficiency for the adjusted one is improved from 69% to 90%. The test result of the diffraction peak of the standard sample Si showed that the adjusted detector module works well.

Spatial resolution determination of a position sensitive ultra-cold neutron detector

The study of the properties of the quantum states of bouncing neutrons requires position sensitive detection with micro-metric spatial resolution. The UCNBoX detector relies on Charge Coupled Devices (CCD) coated with a thin boron-10 conversion layer to detect neutron hits. In this paper, we present an original experimental method to determine the spatial resolution of this device using micrometric masks. The observed resolution is 2.0±0.3μm.

Study of a position-sensitive scintillator neutron detector prototype based on 6LiF/ZnS scintillator and silicon photomultiplier arrays readout

Due to the shortage of the 3He gas and its rapidly increasing price, scintillator detectors, the advantages of which are high spatial resolution and capability of detection in real time, become widely used in many neutron instruments. In this work, a position-sensitive neutron detector consisting of a 6LiF/ZnS scintillation screen and a silicon photomultiplier array linked to a capacitive network to detect the positions of incident neutrons, is constructed and tested. To evaluate the detector performance, a series of neutron beam experiments with the detector prototype were performed in the BL20 at the China Spallation Neutron Source. The spatial resolution was measured, and the energy-selective neutron imaging and Bragg edge measurements of a 316L stainless steel sample were performed. A sub-millimeter spatial resolution could be obtained for the detector prototype under study. The detector with such a high spatial resolution is promising for applications in neutron scattering experimental installations, especially for neutron single-crystal diffractometers.

MBGEM: a stack of borated GEM detector for high efficiency thermal neutron detection

A new position-sensitive thermal neutron detector based on boron-coated converters has been developed as an alternative to today’s standard ^3mathrm{He}-based technology for application to thermal neutron scattering. The key elements of the development are the boron-coated GEM foils (Sauli in Nucl Instrum Methods Phys Res Sect A Accel Spectrom Detect Assoc Equip 386:531, 1997) that are used as a multi-layer neutron converter via the ^{10}mathrm{B}(n,alpha )^7mathrm{Li} reaction together with an efficient collection of the produced secondary electrons. This paper reports the test performed on a 3 layers converter prototype coupled to a GEMPix detector (Murtas in Radiat Meas 138:106421, 2020), carried out in order to study the possibility to produce a large-scale multi-layer neutron detector capable to reach high detection efficiency with high spatial resolution and able to sustain the high neutron flux expected in the new neutron spallation source under development like the ESS.

A position and pulse shape discriminant p-terphenyl detector module

We present the development of a neutron detector array module made with para-terphenyl, a bright, fast, n/γ discriminating crystalline organic scintillator. The module is comprised of 2 cm × 2 cm × 2 cm p-terphenyl crystals that have been optically coupled together to create a pseudo-bar module. While only relying on two photo detectors, the module is capable of distinguishing interactions between up to eight crystals. Furthermore, the module retains the p-terphenyl’s pulse shape discrimination (PSD) capability. Together this makes the pseudo-bar module a promising position-sensitive neutron detector. Here we present characteristics of the pseudo-bar module — its timing resolution as well as its pulse shape and position discrimination capabilities, and briefly discuss future plans for utilizing an array of pseudo-bar modules in a useful neutron detector system.

A low-power preamplifier for resistive charge division position-sensitive neutron detectors

A low power preamplifier solution for use with the rs-p4-0332-203r4 resistive charge distribution neutron detectors is presented in this work. The effects of the ground input impedance caused by the chip and the ground signal undershoot caused by the blocking capacitance are evaluated via simulations. For reference, a reasonable parameter configuration in the structure of a passive filter is sufficient to suppress the effects of both the input impedance and the undershoot. The power per channel in the preamplifier is limited to a maximum of 39 mW. Finally, measurement resolution of 6.8 mm is obtained for the detector.

A Comparative Analysis of the Characteristics of Data Acquisition Systems From Position-Sensitive Neutron Detectors

Abstract—This article discusses the results of parallel measurements with two-coordinate position-sensitive He3 detectors with a delay line, which are installed on REFLEX and GRAINS neutron spectrometers of the IBR-2 pulsed reactor with the simultaneous use of three data acquisition systems: DeLiDAQ-1, DeLiDAQ-2, and a system based on the N6730 digitizer produced by CAEN.

Hybrid boron-10 gaseous detector for slow and fast neutron simultaneous detection

A hybrid position-sensitive neutron detector with active 10B-layer and proportional chamber filled by the gas mixture Ar+25%CO2 is being studied. The detector is used on the neutron source based at the linear accelerator. Recording two pairs of pulse heights which are produced in two gas gaps by 7Li and 4He nuclei between the anode and two cathodes gives a possibility to determine the X and Y neutron coordinates. This detector permits time-of-flight measurements. A significant difference in pulse height spectra for slow and fast (several MeV) neutrons was observed in experiment. In recent experiments with 10B-detector we found that (1) the pulse heights depend on the neutron energy and (2) the position of the maximum in the pulse height spectrum varies monotonically versus the maximum neutron energy.

Measurement of the total neutron-scattering cross-section ratios of noble gases of natural isotopic composition using a pulsed neutron beam

Precision measurements of slow neutron cross sections with atoms have several scientific applications. In particular the n-$^{4}$He s-wave scattering length is important to know both for helping to constrain the nuclear three-body interaction and for the proper interpretation of several ongoing slow neutron experiments searching for other types of neutron-atom interactions. We present new measurements of the ratios of the neutron differential scattering cross sections for natural isotopic-abundance mixtures of the noble gases He, Ar, Kr, and Xe to natural isotopic abundance Ne. These measurements were performed using a recently developed neutron scattering apparatus for gas samples located on a pulsed slow neutron beamline which was designed to search for possible exotic neutron-atom interactions and employs both neutron time of flight information and a position-sensitive neutron detector for scattering event reconstruction. We found agreement with the literature values of scattering cross sections inferred from Ar/Ne, Kr/Ne and Xe/Ne differential cross section ratios over the $q$ range of $1 - 7$ nm$^{-1}$. However for the case of He/Ne we find that the cross section inferred differs by 11.3% (7.6 $\sigma$) from previously-reported values inferred from neutron phase shift measurements, but is in reasonable agreement with values from other measurements. The very large discrepancy in the He/Ne ratio calls for a new precision measurement of the n-$^{4}$He scattering length using neutron interferometry.

Data Correction Method for Improving the Spatial Resolution of a Position-Sensitive 10B Neutron Detector

A technique for correcting experimental data from a position-sensitive neutron detector with an active layer of solid boron-10, where the charge division method is used to determine the coordinate, is proposed. This technique relies on the signal amplitude loss in a distributed resistance circuit. Each resistance is connected to two adjacent wires of the anode (or to two adjacent strips of the cathode) of the detector. This readout method is simple to implement and does not require complex and expensive electronics. However, unlike the distributed delay line method, it requires that the nonlinear dependence of the coordinate both on the ratio of the measured amplitudes and on the sum of these amplitudes be taken into account when the neutron coordinate is calculated. Test measurements with a signal generator were conducted to determine the dependence of coordinates on the ratio of pulse amplitudes from two ends of the distributed resistance. This dependence is approximated by a third-order polynomial. At the same time, the coefficients of this polynomial depend on the sum of amplitudes of pulses at the outputs of two amplifiers connected to the two ends of the distributed resistance. The amplitude dependences of these coefficients are also approximated by third-order polynomials. Thus, the spatial resolution of the detector depends on the signal amplitudes and on the coordinate itself. It is possible to determine the signal amplitudes and neutron coordinates more accurately by correcting the data. The procedure also improves the integral uniformity of the coordinate distribution. Following the application of the proposed correction, the spatial resolution of the neutron detector improved from 2 to 1.5 mm along the x axis.

Optimization and characterization of the PGAI-NT instrument’s Neutron Tomography set-up at MLZ

The Prompt Gamma-ray Activation Imaging and Neutron Tomography (PGAI-NT) instrument at the PGAA facility of the Heinz Maier-Leibnitz Center (MLZ), provides a method to obtain and effectively visualize position-sensitive element abundances in samples by combining a three-dimensional extension of Prompt Gamma-ray Activation Analysis (PGAA) and Neutron Tomography (NT). Inspired by a proof-of-principle study, a cone-beam tomography set-up was designed, tested and installed. This article reports on the design of the new cone-beam tomography set-up and its optimization using neutron beam simulations and physical measurements. A new position-sensitive neutron detector with improved performance and instrument environment integration was designed, built and tested. The overall NT performance of the set-up is investigated in the course of a Quality Assessment for neutron tomography sites. Its stand-alone NT and all-in-one PGAI-NT suitability is determined.

Upgrade to the MAPS neutron time-of-flight chopper spectrometer.

The MAPS direct geometry time-of-flight chopper spectrometer at the ISIS pulsed neutron and muon source has been in operation since 1999, and its novel use of a large array of position-sensitive neutron detectors paved the way for a later generations of chopper spectrometers around the world. Almost two decades of experience of user operations on MAPS, together with lessons learned from the operation of new generation instruments, led to a decision to perform three parallel upgrades to the instrument. These were to replace the primary beamline collimation with supermirror neutron guides, to install a disk chopper, and to modify the geometry of the poisoning in the water moderator viewed by MAPS. Together, these upgrades were expected to increase the neutron flux substantially, to allow more flexible use of repetition rate multiplication and to reduce some sources of background. Here, we report the details of these upgrades and compare the performance of the instrument before and after their installation as well as to Monte Carlo simulations. These illustrate that the instrument is performing in line with, and in some respects in excess of, expectations. It is anticipated that the improvement in performance will have a significant impact on the capabilities of the instrument. A few examples of scientific commissioning are presented to illustrate some of the possibilities.

Boron-10 lined RPCs for sub-millimeter resolution thermal neutron detectors: Feasibility study in a thermal neutron beam

The results of an experimental feasibility study of a position sensitive thermal neutron detector based on a resistive plate chamber (RPC) are presented. The detector prototype features a thin-gap (0.35 mm) hybrid RPC with an aluminium cathode and a float glass anode. The cathode is lined with a 2 μm thick 10B4C neutron converter enriched in 10B. A detection efficiency of 6.2% is measured at the neutron beam (λ = 2.5 Å) for normal incidence. A spatial resolution better than 0.5 mm FWHM is demonstrated.

Multiplexing readout method based on switch arrays for position sensitive thermal neutron detectors

To address complexities arising from the increased number of readout channels in large scale neutron detection or imaging systems, a multiplexing readout method is introduced. The proposed method can greatly reduce the scale and cost of the readout electronics. To evaluate the readout method, a prototype involving a front-end circuit and a signal multiplexed circuit for detectors such as multiwire proportional chamber (MWPC), gaseous electron multipliers (GEM) and micro-channel plates (MCP) is evaluated in the laboratory. The multiplexing circuit consists of a switch array and a high speed analog to digital converter (ADC). By controlling the switch timing, multi-channel signals can be readout through only one ADC channel, thereby reducing the number of channels required for readout. Furthermore, the readout speed can be adjusted by changing the switching frequency. The results show that the multiplexing readout method is feasible, and the position resolution for thermal neutron detectors is good. The evaluation board is used to simulate the MWPC detector with 2 mm spacing and a position resolution of 35 μm is obtained with event rate up to 2 MHz. Besides, joint test with a thick gaseous electron multipliers (TGEM) detector with 0.8 mm spacing yields a position resolution of about 400 μm.

Optical identification and quantification of single neutron detection in 6LiF/ZnS scintillators using a CMOS camera

The possibility of observing the light from single neutron detection in scintillation materials by highly pixelated silicon sensors coupled with a demagnification optical lens could lead to a new generation of position-sensitive neutron detectors with relatively large area coverage and competitive spatial resolution. Several ZnS/6LiF-based scintillators were tested at the SINQ Beamline for Neutron Optics (BOA) using a neutron radiography setup mounting a sCMOS camera with an f/0.95 commercial objective. Single neutrons were identified and distinguished from the camera noise and particles detected directly in the silicon sensor in all the tested scintillators, with exposures starting from 1 ms. Linearity between neutron counting and exposure times was obtained from 10 ms up to 200 ms.

Simulations and systematic neutron beam characterisations on two-dimensional position-sensitive neutron detector multi-wire proportional counter with delay-line readout

A two-dimensional position-sensitive neutron detector multi-wire proportional counter (MWPC) was systematically characterised on dedicated detector test station V17 at reactor BER2 of HZB. Performances including characteristic anode curve, characteristic drift curve, detection efficiency, efficiency homogeneity, horizontal position resolution, vertical position resolution, counting rate capability, and gamma sensitivity were measured. In addition, systematic simulations were conducted based on the detector configurations. These systematic studies are presented here for the first time. They assist in obtaining a greater understanding of detector performances, form the methodology for detector characterisations by reactor neutron beams, and can be used as references for neutron detector research and applications.