High-intensity Neutron Research Articles

Novel concept for a neutron electric charge measurement using a Talbot-Lau interferometer at a pulsed source

A concept to measure the neutron electric charge is presented which employs a precision Talbot-Lau interferometer in a high-intensity pulsed neutron beam. It is demonstrated that the sensitivity for a neutron charge measurement can be improved by up to two orders of magnitude compared to the current best direct experimental limit.

Fenghuang: High-intensity multi-section neutron powder diffractometer at CMRR

Fenghuang has been upgraded to be the first neutron powder diffractometer at the China Mianyang Research Reactor (CMRR) dedicated to research on the microstructure of materials. It was firstly built in 2005 at the Swimming Pool Research Reactor-300 (SPRR-300) in Mianyang, and then moved to CMRR in 2013. Through the combination of a horizontally focusing neutron guide and a vertically focusing monochromator, the neutron flux at the sample position is up to 2.84 × 106 n s−1cm−2. The resolution of the diffractometer can be adjusted by a horizontal slit for different sample. The superposition scan mode enables each detector to measure the complete diffraction pattern and simplifies the correction of the efficiency of the counting channels. This diffractometer is equipped with temperature and pressure devices, and can be used for research at ambient and extreme conditions.

Preliminary design study of a simple neutron energy spectrometer using a CsI self-activation method for daily QA of accelerator-based BNCT

ABSTRACT For recent boron neutron capture therapy (BNCT), accelerator-based neutron sources have been actively developed in place of reactor-based neutron sources. In this study, a novel neutron energy spectrometer for the daily quality assurance (QA) of BNCT was designed on the basis of a CsI self-activation method for accelerator-based neutron sources. The spectrometer design was optimized in terms of its energy resolution. To verify its applicability to high-intensity BNCT neutron fields, some practical simulations were performed. It was shown that the designed spectrometer was able to evaluate a neutron energy spectrum in approximately 900 s after an instantaneous neutron irradiation. In addition, its energy resolution was sufficient for detecting an unexpected distortion in the spectrum. The results confirm that the designed spectrometer can be employed for the daily QA of BNCT to check that the expected spectrum remains unchanged.

The design and thermo-structural analysis of target assembly for high intensity neutron source

The engineering design of an integrated target assembly of IFMIF lithium target was performed in IFMIF/EVEDA project for a high intensity neutron source. In the evaluation of the design, a thermos-structural analysis of was evaluated by ABAQUS code, and the modeling region was a part of the target assembly which was from the inlet nozzle to the outlet pipe. The material of the target assembly including the back plate was F82H steel. In the thermal-structural analysis, the normal operations and start/stop or abnormal operations were evaluated at 250 or 300 °C operation of Li flow in inlet pipe. The result showed that the temperature of the target assembly was evaluated to be still lower than the Li boiling point of 344 °C under a vacuum pressure of 10−3 Pa. In a temperature constant operation, the calculated stresses and displacements were small enough for thermal soundness of the target assembly in steady states. In a transient cooling process from 300 °C to 20 °C through 250 °C, the maximum Mises stress was found to be 372 MPa, which was lower than the yield stress at 300 °C.

Pendellösung interferometry by using pulsed neutrons

Pendellösung interferometry is one of the technique for accurate determination of the structure factors of crystals. Observation method of Pendellösung fringes by using pulsed cold neutrons and the time-of-flight analysis were established. We measured the nuclear scattering length of silicon by the Pendellösung fringes with pulsed neutrons as (4.125±0.003(stat.)±0.028(syst.)). This indicates the applicability of Pendellösung interferometry at high-intensity pulsed neutron facilities for various precision measurements.

Experimental validation of the brightness distribution on the surfaces of coupled and decoupled moderators composed of 99.8% parahydrogen at the J-PARC pulsed spallation neutron source

Liquid hydrogen moderators composed of 99.8% parahydrogen associated with light-water premoderator at the J-PARC pulsed spallation neutron source have demonstrated high performance in the extraction of high intensity cold and thermal neutron beams. In the design stage, simulations have shown not only high total neutron intensity in the coupled moderator but also a local neutron-brightness increase at its edges. The edge-effect-brightness increase is also exploited in the design of the European Spallation Source (ESS) moderators, which are also based on 99.8% parahydrogen, but are thin (thickness: 3 cm) to further increase brightness. In this study, the spatial distribution of the neutron brightness at the surface of the coupled moderator in the J-PARC pulsed spallation neutron source was directly measured to experimentally validate the calculated edge-brightness enhancement. The brightness distribution at the moderator surface predicted by Monte Carlo simulation was clearly observed. As a result, the validity of the simulation tools used in the design-optimization process of the J-PARC and ESS moderator is confirmed.

Study on the Performance of the Neutron Diffractometer (HIPD at CARR) by Monte Carlo Simulation and Convolution Methods

The compromise between intensity and resolution is the core issue for the powder neutron diffraction techniques. An investigation of the optimum configuration of a neutron instrument is necessary to meet the requirement for both the intensity and resolution before the final construction. In this paper, the performance of the high-intensity powder neutron diffractometer (HIPD) at China Advanced Research Reactor has been studied by Monte Carlo simulation and convolution methods. The virtual detector Monitor-nD with super fine recording elements was used to record the diffraction patterns of the simulated HIPD. In order to introduce the spatial resolution effect of the detector in the diffraction pattern, the convolution method was adopted. The diffraction peaks from the diffraction patterns were then used to calculate the minimum interplanar spacing difference $\Delta d$ that the HIPD can distinguish. It is obtained that the minimum resolution of the HIPD is $2.08 \times 10^{-3}$ ( $\Delta d/d$ ) for the current design. The resolution of the HIPD calculated above is consistent with the resolution actually measured according to the Ni sample diffraction experiment. This indicates that the above simulation method has high reliability. Finally, a movable $20^{\prime }$ Soller collimator and sample cans with 3 and 6 mm diameters are recommended to be used to optimize the ND experiment. After installing the $20^{\prime }$ Soller collimator, the minimum resolution can be $1.88 \times 10^{-3}$ ( $\Delta d/d$ ). The diffraction intensity of the 6-mm-diameter sample will be almost 3 times higher than that of the 3-mm-diameter sample.

Saclay Compact Accelerator-driven Neutron Sources (SCANS)

For next decade, the European neutron scattering community will face of important changes, as many facilities will close, strictly fission-based sources. This statement mainly concerns France with the planned closure of Orphee and ILL. At CEA-Saclay, the project SONATE has been launched in order to provide a high intensity neutron source in Saclay site, this project is based on Compact Accelerator-driven Neutron Sources technology coupled to high-intensity beams. The goal of SONATE is to develop a 50 kW target, aiming to produce at least a neutron yield of 1013 s-1 in pulse mode with a peak current of 100 mA. We have investigated in this document the best combinations of beam/target which would lead to this substantial neutron yields. Further investigations and tests have to be carry out, especially due to sparse data on thick target and such low-energy beams considered in this document. An intermediate step to the SONATE project is under test and development, called IPHI-NEUTRON, which would lead to provide a small-size neutron facility mainly devoted to neutron imagery for industry. This step is based on the existing 3 MeV proton beam, named IPHI. Best target candidates are Lithium and Beryllium, leading respectively to a neutron yield of about 2.1013 s-1 and 4.1012 s-1.

Neutronics Analyses for the ORNL’s Spallation Neutron Source Second Target Station

This paper presents an update of the status of the neutronics analyses performed for the Second Target Station (STS). The target station is driven with short (less than 1 micro second long) proton pulses at 15 Hz repetition rate and 700 kW proton beam power. The target will be optimized for high intensity and high resolution long wavelength neutron applications. The STS will accommodate 22 beamlines and will expand and complement the current national neutron scattering capabilities. The proton beam footprint as small as acceptable from the mechanical and heat removal aspects is planned to generate a compact-volume neutron production zone in the target, which is essential for tight coupling of the target and the moderators and for achieving high-intensity peak thermal and cold neutron fluxes. Present efforts to develop high fidelity engineering models for neutronics analyses with automatic CAD-to-MCNP conversion are described. Heating rates and radiation damage, which provide input in the engineering design are presented and the performance of the moderators is briefly addressed.

Validation of Geant4 simulation tool for low energy proton induced reactions

With the development of high-intensity accelerators, it is now envisaged to build compact high-intensity neutron sources for various applications. At the CEA Saclay, we have started a project to promote such technology based on the existing 100 mA IPHI proton injector. We are focusing our interest on low-energy proton-induced reactions (less than 20 MeV) to provide an economical way to produce neutrons and also to limit the radiological constraints. Optimization studies of the target-moderator assembly require validated simulation tools in order to maximize the neutron flux. In this document, the development status of the GEANT4-based simulation tool is presented, as well as its validation by comparison with gold foil activation measurements on the IPHI proton injector. The experimental setup and the simulation procedure are described. A good agreement is obtained between experimental data and simulation results when considering angular distribution of primary neutrons provided by Howard and Yanch’s measurements.

The high-intensity option of the SANS diffractometer KWS-2 at JCNS - characterization and performance of the new multi-megahertz detection system.

A new detection system based on an array of 3He tubes and innovative fast detection electronics has been installed on the high-intensity small-angle neutron scattering (SANS) diffractometer KWS-2 operated by the Jülich Centre for Neutron Science (JCNS) at the Heinz Meier-Leibnitz Zentrum in Garching, Germany. The new detection system is composed of 18 eight-pack modules of 3He tubes that work independently of one another (each unit has its own processor and electronics). To improve the read-out characteristics and reduce the noise, the detection electronics are mounted in a closed case on the rear of the 3He tubes' frame. The tubes' efficiency is about 85% (for λ = 5 Å) and the resolution slightly better than 8 mm. The new detection system is characterized by a dead-time constant of 3.3 µs per tube and an overall count rate as high as 6 MHz at 10% dead-time loss. Compared with the old detector this is an improvement by a factor of 60. The much higher count rate will shorten the measurement times and thus increase the number of experiments possible in a given time period by the optimal use of the high flux of up to 2 × 108 n cm-2 s-1 at the sample position. Combined with the event-mode operation capability, this will enable new scientific opportunities in the field of structural investigations of small soft-matter and biological systems. The implementation of the detector in the high-intensity concept on KWS-2, its characterization and its performance based on test experiments are reported in this paper.

Improved yield and control of spectra from high-intensity laser-generated neutron beams

AbstractKinetic modeling of laser-ion beam generation from the “break-out afterburner” (BOA) has been modeled for several deuteron-rich solid-density target foils. Modeling the transport of these beams in a beryllium converter shows as much as a fourfold increase in neutron yield over the present state of the art through the use of alternative target materials. Additionally, species-separation dynamics during the BOA can be exploited to control the hardness of the neutron spectra, of interest for, for example, enhancing penetrability in shielded material in active neutron interrogation settings.

Recent developments of the FALSTAFF experimental setup

The study of nuclear fission is encountering renewed interest with the development of GEN-IV reactor concepts, mostly working in the neutron fast energy domain. To support the fast reactor technologies, new high quality nuclear data are needed. New facilities are being constructed to produce high intensity neutron beams from hundreds of keV to few tens of MeV (Licorne, NFS, nELBE, ...). They will open new opportunities to provide nuclear data. In this framework the development of an experimental setup called FALSTAFF for a characterisation of actinide fission fragments has been undertaken. Fission fragment yields and associated neutron multiplicities will be measured as a function of the neutron energy. Based on time-of-flight and residual energy technique, the setup will allow the simultaneous measurement of the complementary fragment velocity and energy. The FALSTAFF setup and the upgrade of the first arm prototype with the new ionisation chamber CALIBER will be presented. The performances of the experimental apparatus is discussed.

Neutron Imaging Facilities in a Global Context

Neutron Imaging (NI) has been developed in the last decades from a film-based inspection method for non-destructive observations towards a powerful research tool with many new and competitive methods. The most important technical step forward has been the introduction and optimization of digital imaging detection systems. In this way, direct quantification of the transmission process became possible—the basis for all advanced methods like tomography, phase-contrast imaging and neutron microscopy. Neutron imaging facilities need to be installed at powerful neutron sources (reactors, spallation sources, other accelerator driven systems). High neutron intensity can be used best for either highest spatial, temporal resolution or best image quality. Since the number of such strong sources is decreasing world-wide due to the age of the reactors, the number of NI facilities is limited. There are a few installations with pioneering new concepts and versatile options on the one hand, but also relatively new sources with only limited performance thus far. It will be a challenge to couple the two parts of the community with the aim to install state-of-the-art equipment at the suitable beam ports and develop NI further towards a general research tool. In addition, sources with lower intensity should be equipped with modern installations in order to perform practical work best.

In-situ time-of-flight neutron diffraction study of the structure evolution of electrode materials in a commercial battery with LiNi0.8Co0.15Al0.05O2 cathode

A commercial lithium-ion battery with LiNi0.8Co0.15Al0.05O2 (NCA) cathode has been studied in situ using high-intensity and high-resolution neutron diffraction. Structure and phase composition of the battery electrodes have been probed during charge-discharge in different cycling modes. The dependence of the anode composition on the charge rate has been determined quantitatively. Different kinetics of Li (de)intercalation in the graphite anode during charge/discharge process have been observed. Phase separation of the cathode material has not been detected in whole voltage range. Non-linear dependencies of the unit cell parameters, atomic and layer spacing on the lithium content in the cathode have been observed. Measured dependencies of interatomic spacing and interlayer spacing, and unit cell parameters of the cathode structure on the lithium content could be qualitatively explained by several factors, such as variations of oxidation state of cation in oxygen octahedra, Coulomb repulsion of oxygen layers, changes of average effective charge of oxygen layers and van der Waals interactions between MeO2-layers at high level of the NCA delithiation.

A new method of creating high intensity neutron source

We propose a new scheme of producing an intense neutron beam whose yields may exceed those of the existing facilities by a few to several orders of magnitude in the sub-eV region. This scheme employs a MeV gamma beam extracted from circulating quantum ions, which has been recently proposed. The gamma beam is directed to a deuteron target and the photo-disintegration process generates a neutron beam. The calculated neutron energy spectrum is nearly flat down to the neV range, and thus there exists a possibility to utilize a good quality of neutrons especially in sub-eV energy region without using a moderator.

Structure of a Novel Spinel Li0.5Zn5/3Sb2.5/3O4 by Neutron and Synchrotron Diffraction Analysis

Zn7/3Sb2/3O4 is a secondary phase in ZnO-based varistors. Acceptor impurities, such as Li+, increase the resistivity. This effect is produced by a modification of the grain boundary barriers. The role of the cationic distribution in the mentioned events is worth clarifying. The Li0.5Zn5/3Sb2.5/3O4 room-temperature structure was determined by means of a neutron diffraction and synchrotron X-ray diffraction investigation. The title compound was prepared by conventional ceramic process. The elemental composition of the investigated sample was verified by means of electron microscopy—energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The neutron experiment was performed at the high-intensity neutron diffractometer with position-sensitive detector at the D1B beamline of the Laue-Langevin Institute, Grenoble. The high resolution synchrotron measurement was carried out at MCX beamline of Elettra Sincrotrone Trieste. Rietveld analysis was performed with the FullProf program. Li0.5Zn5/3Sb2.5/3O4 belongs to the spinel family, space group F d 3 ¯ m (227). The measured lattice parameter is a = 8.5567(1) Å. The Li+1 and Zn+2 ions are randomly distributed among the tetrahedral and octahedral sites as opposed to Sb+5 ions which have preference for octahedral sites. Fractional coordinate of oxygen, u = 0.2596(1), indicates a slight deformation of the tetrahedral and octahedral sites. The data given in this paper provide structural support for further studies on measurements and microscopic explanations of the interesting properties of this family of compounds.

Simulation of the Effect of Burnup of Materials of an Ionization-Chamber Radiator by the Monte Carlo Method

Using the Monte Carlo method, the authors have modeled the burnup of fissionable material of the radiator of an ionization chamber in a neutron flux. A study has been made of the change in the sensitivity of the ionization chamber with time because of the burnup of fissionable material of the radiator for low- and high-intensity neutron fluxes having different energies.

Development of high sensitivity 4H-SiC detectors for fission neutron pulse shape measurements.

4H-silicon carbide (4H-SiC) detectors are well suited for measurements of fission neutron pulse shape for their compact size, excellent radiation resistance, and hydrogen free composition. The aim of this study is to improve the 4H-SiC detector's sensitivity to fission neutron pulses. 4H-SiC detectors with varied epilayer thicknesses are fabricated and then tested in the pulsed neutron field of the Chinese Fast Burst Reactor II (CFBR II). The sensitivity of the 4H-SiC detector to the CFBR II neutron pulse is increased by 139.8%, with the enlargement of epilayer thickness from 20 μm to 120 μm. By employing the proton-recoil method, the sensitivity of the 4H-SiC detector to the CFBR II neutron pulse is further increased by 11.6%. With enhanced sensitivity to fission neutron pulses, 4H-SiC detectors are promising devices for high intensity neutron pulse measurements.

A proposal for an alternative use of prompt-Self Powered Neutron Detectors: Online spectral-deconvolution for monitoring high-intensity neutron flux in LFRs

Self-Powered Neutron Detectors (SPNDs) are currently used in reactors’ environment to sense the magnitude of neutron-fluxes, usually for spatial-distribution mapping of the fuel region as to optimize burn-up strategies. During the development of tailored instrumentation for Lead-cooled Fast Reactors, the possibility to perform online spectral deconvolution of fast neutron-fluxes was recognized. Seven geometrically similar SPNDs with different neutron-sensitive materials, have been characterized by the Monte Carlo transport code MCNPX. Thanks to a database of spectral sensitivities vs. neutrons’ energy, a mathematical deconvolution process from 7 electric current values virtually measured by SPNDs was started, retrieving spectral information, in terms of 7 energy windows, of the neutron-flux the detectors are subjected by. This paper describes the procedure that led to those results, prefiguring future development to improve proposed method.