Pulsed Neutron Source Research Articles

Development of a multi-layer high-efficiency GEM-based neutron detector for spallation sources

Neutron detection is nowadays mostly based on 3He gas detectors, but its shortage and the continuous upgrades of the neutron facilities require new devices to perform experiments with maximum performances. This work presents a new detector based on the Gas Electron Multiplier (GEM) combined with several boron layers. This detector combines the features of GEM technology with the properties of boron as a neutron converter and the device is produced to sustain high neutron fluxes with high detection efficiency. The detector has been characterised at the ISIS Pulsed Neutron and Muon Source (UK). Based on the analysis of our results, the detector has shown a good response to thermal and epithermal neutrons reaching a detection efficiency of 16% at 1.8 Å (25 meV). The good detection efficiency (even increasable with the addition of further boron GEM foils) and the good time resolution, make the detector a unique device for the neutron techniques. In particular, its use can easily be envisaged in techniques involving neutron transmission measurements, that require high fluxes impinging on the detectors, with the added bonus of a 2D-resolved capability due to the padded anode.

Directed pulsed neutron source generation from inverse kinematic reactions driven by intense lasers

Neutron production driven by intense lasers utilizing inverse kinematic reactions is explored self-consistently by a combination of particle-in-cell simulations for laser-driven ion acceleration and Monte Carlo nuclear reaction simulations for neutron production. It is proposed that laser-driven light-sail acceleration from ultrathin lithium foils can provide an energetic lithium-ion beam as the projectile bombarding a light hydrocarbon target with sufficiently high flux for the inverse p(Li7,n) reaction to be efficiently achieved. Three-dimensional self-consistent simulations show that a forward-directed pulsed neutron source with ultrashort pulse duration 3 ns, small divergence angle 26°, and extremely high peak flux 3 × 1014n/(cm2⋅s) can be produced by petawatt lasers at intensities of 1021 W/cm2. These results indicate that a laser-driven neutron source based on inverse kinematics has promise as a novel compact pulsed neutron generator for practical applications, since the it can operate in a safe and repetitive way with almost no undesirable radiation.

A pulsed neutron source with a sealed dense plasma focus chamber

Compared with other pulsed neutron sources, dense plasma focus (DPF) devices have the advantages of simple in construction, extremely compact and cost-effective. In this paper, a DPF device was developed for used as pulsed neutron source. The Mather-type sealed chamber was adopted for long duration and multishot operations without vacuum system, which is convenient for transport, use and storage. The maximum D-D neutron yield of the device is approximately 1.1 × 109 n/pulse when the storage capacitors are charged with 22 kV and the deuterium gas filling pressure is 750 Pa. The neutron pulse width (FWHM) was measured to be 45 ns ± 10 ns.

Characteristics of a neutron source based on an electron accelerator LINAC-200

As part of the commissioning work at the linear electron accelerator LINAC-200 (JINR), we conducted experiments to study the characteristics of a pulsed neutron source obtained by irradiating a converter target with a 140 MeV electron beam. To estimate neutron source parameters and neutron energy spectra in lead and tungsten targets with different sizes numerical simulations were performed. Additionally, we have conducted experiments to measure the energy spectra of neutrons and gamma rays using high-resolution time-of-flight method. It has been found that the ratio of integral estimates between the calculated and average measured neutron yields (for tungsten and lead targets) did not exceed 30%. The fluence of resonant and thermal neutrons in the target is estimated at 2.8×1013 neutrons per second, which corresponds to the requirements for modern pulsed neutron sources.

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.

HighNESS conceptual design report: Volume I

The European Spallation Source, currently under construction in Lund, Sweden, is a multidisciplinary international laboratory. Once completed to full specifications, it will operate the world’s most powerful pulsed neutron source. Supported by a 3 million Euro Research and Innovation Action within the EU Horizon 2020 program, a design study (HighNESS) has been completed to develop a second neutron source located below the spallation target. Compared to the first source, designed for high cold and thermal brightness, the new source has been optimized to deliver higher intensity, and a shift to longer wavelengths in the spectral regions of cold (CN, 2–20 Å), very cold (VCN, 10–120 Å), and ultracold (UCN, >500 Å) neutrons. The second source comprises a large liquid deuterium moderator designed to produce CN and support secondary VCN and UCN sources. Various options have been explored in the proposed designs, aiming for world-leading performance in neutronics. These designs will enable the development of several new instrument concepts and facilitate the implementation of a high-sensitivity neutron-antineutron oscillation experiment (NNBAR). This document serves as the Conceptual Design Report for the HighNESS project, representing its final deliverable.

Design of the cryogenic moderator system for the second target station

The Second Target Station (STS) at Oak Ridge National Laboratory will be a 700 kW pulsed spallation neutron source designed to provide the world’s highest brightness cold neutron beams. In order to produce the required neutron performance, two compact liquid hydrogen moderators are located adjacent to the tungsten spallation target and must be supplied with less than 20 K hydrogen and a para hydrogen fraction of 99.8% or greater. The Cryogenic Moderator System (CMS) will consist of a single hydrogen loop feeding the two moderators in series cooled by a helium refrigerator with a cooling capacity of 2.5 kW at 17 K. The hydrogen loop consists of a hydrogen circulator, hydrogen helium heat exchanger, ortho-para converter, accumulator, transfer lines and heater. The design of the hydrogen loop is based on the CMS design of the First Target Station at the Spallation Neutron Source and some of the component designs may be reused. General hydrogen temperature control is provided by controlling the flowrate of helium to the heat exchanger. The hydrogen loop will have a constant flowrate of 0.5 L/s and remove a nuclear heat load of about 850 W from the two moderators, which is deposited both directly in the hydrogen and the adjacent hydrogen containing structures. Because the nuclear heat load is accelerator driven, the hydrogen system must remain stable when the heat load is removed instantaneously during beam trips. System stability is maintained passively with the accumulator and actively with the heater. Ionizing radiation which interacts with the liquid hydrogen drives backconversion of the hydrogen from parahydrogen to orthohydrogen. The STS moderator performance is very sensitive to small fractions of orthohydrogen requiring an ortho-para converter to maintain the hydrogen supplied to the moderators at near equilibrium parahydrogen concentration. STS CMS is in the early stage of preliminary design and current focus is evaluating component sizing and system stability during beam transients.

Nanocomposite materials as observed by mass-selective neutron spectroscopy

Abstract This work provides a current, critical view of the application of MAss-selective Neutron SpEctroscopy (MANSE) to nanocomposite materials. MANSE is a unique technique made possible owing to the existence of the pulsed neutron sources. At present, the only operating MANSE spectrometer in the world, VESUVIO, is located at the ISIS Neutron and Muon Source in the UK. We start by providing a brief description of the neutron Compton scattering, the anatomy of a mass-selective neutron spectrometer, and the experimental data treatment. We continue by briefly outlining the main quantum mechanical concepts, models and approximations relevant both to the ab initio prediction and experimental measurement of main MANSE observables. Next, we present several recent exemplars chosen to highlight the use of MANSE in the field of nanocomposites. Our examples include, in chronological order, encapsulated nanoparticles in amorphous silica gel, bioactive glass-ionomer cement, Cu-Ti-C composites, and sodium carboxymethyl starch-based binders in the presence of a mineral matrix. We close by providing our view of the ongoing and future challenges and opportunities in the mass-selective neutron investigation of NQEs in nanocomposite materials.

Development of Neutron Interferometer Using Multilayer Mirrors and Measurements of Neutron-Nuclear Scattering Length with Pulsed Neutron Source.

This study entailed the successful deployment of a novel neutron interferometer that utilizes multilayer mirrors. The apparatus facilitates a precise evaluation of the wavelength dependence of interference fringes utilizing a pulsed neutron source. Our interferometer achieved an impressive precision of 0.02rad within a 20-min recording time. Compared to systems using silicon crystals, the measurement sensitivity was maintained even when using a simplified disturbance suppressor. By segregating beam paths entirely, we achieved successful measurements of neutron-nuclear scattering lengths across various samples. The values measured for Si, Al, and Ti were in agreement with those found in the literature, while V showed a disparity of 45%. This discrepancy may be attributable to impurities encountered in previous investigations. The accuracy of measurements can be enhanced further by mitigating systematic uncertainties that are associated with neutron wavelength, sample impurity, and thickness. This novel neutron interferometer enables us to measure fundamental parameters, such as the neutron-nuclear scattering length of materials, with a precision that surpasses that of conventional interferometers.

A neutron trigger detector for pulsed reactor neutron sources

A variety of experiments investigating properties of neutrons can be performed at pulsed reactor neutron sources like the research reactor TRIGA Mainz. A typical problem faced by these experiments is the non-availability of a reliable facility-provided trigger signal in coincidence with the neutron production. Here we present the design and implementation of a neutron pulse detector that provides a coincident trigger signal for experimental timing with a relative precision of 4.5ms.

The lifetime distribution of finite fission chain group around the prompt criticality

In order to describe the behavior of finite fission chains in a fission system initiated by a δ neutron source, we present the conception of the finite fission chains group (FFCG). The group is the collectivity of the fission chains initiated by plenty of neutrons at the same time. Based on the result of the solving generating function, we deduced the lifetime distribution formula of FFCG based on the point kinetics model. Finally, the formula is validated by the experiment with a single pulse neutron source in CFBR-Ⅱ.

Measurement of Isfahan heavy water zero-power reactor kinetic parameters using advanced pulsed neutron source method in a near critical state

The pulsed neutron source (PNS) technique was used to determine the prompt neutron decay constant for two different lattice pitches in the HWZPR heavy water zero power reactor. The results were compared to the variance-to-mean ratio (VTM) method. The neutron mean generation time was also calculated for both pitches, and the results were compared to previous Monte Carlo calculations. The findings of this research can be used as a benchmark nuclear codes to validate kinetic parameters.

Measurement of Mechanical Behavior of 11B-Enriched MgB2 Wire Using a Pulsed Neutron Source

MgB2 represents a hexagonal superconductive material renowned for its straightforward composition, which has facilitated the development of cost-effective practical wires. Its capacity to function at temperatures as low as liquid hydrogen (LH2) has made it a prominent candidate as wire material for the coils of next-generation fusion reactors. Much like other superconducting wires, a prevalent issue arises when these wires are employed in coils, wherein electromagnetic forces induce tensile stress and strain within the wire. This, in turn, diminishes the critical current, which is the maximum current capable of flowing within the generated magnetic field and strain. The techniques and methods for accurately measuring the actual strain on the filaments are of paramount importance. While strain measurements have been conducted with synchrotron radiation and neutrons for other practical wires in the past, no such measurements have been undertaken for MgB2. Presumably, this lack of measurement is attributed to its relatively greater thickness, making it less suitable for synchrotron radiation measurements. Additionally, the high absorption cross-section of the included boron-10 poses challenges in obtaining elastic scattering data for neutron measurements. In response, we fabricated a wire enriched with boron-11, an isotope with a smaller neutron absorption cross-section. We then embarked on the endeavor to measure its strain under tensile loading using pulsed neutrons. Consequently, we succeeded in obtaining changes in the lattice constant under tensile loading through Rietveld analysis. This marks the inaugural instance of strain measurement on an MgB2 filament, signifying a significant milestone in superconductivity research.

Residual strain investigation of a polycrystalline quartzite rock sample using time-of-flight neutron diffraction

In this work, we studied the residual micro lattice strain of an onyx sample, which is a micro- to the cryptocrystalline variety of the mineral quartz SiO2. That the investigation has been carried out using in-situ stress experiments with the time-of-flight neutron diffraction method. The aim of the study is to investigate residual lattice strains and pressure directions in the sample using time-of-flight neutron diffraction, which is a powerful tool for the study of the residual strain behavior in bulk materials, like geological rock samples containing large grains. The residual strain was detected in different sample directions turning the sample in steps of 30° by 180° around the cylindrical z-axis. These experiments have been performed at the time-of-flight neutron strain diffractometer EPSILON, situated on the pulsed neutron source IBR-2M of the Joint Institute for Nuclear Research in Dubna, Russia. The results of this study will provide insights into the compressional and tensional residual strain of the crystallographic lattice planes, and will have implications for our understanding of the tectonic history of this region. These different strains are arranged in the sample by a sinusoidal distribution in radial directions.

Cavitation Damage Prediction in Mercury Target for Pulsed Spallation Neutron Source Using Monte Carlo Simulation.

Cavitation damage on a mercury target vessel for a pulsed spallation neutron source is induced by a proton beam injection in mercury. Cavitation damage is one of factors affecting the allowable beam power and the life time of a mercury target vessel. The prediction method of the cavitation damage using Monte Carlo simulations was proposed taking into account the uncertainties of the core position of cavitation bubbles and impact pressure distributions. The distribution of impact pressure attributed to individual cavitation bubble collapsing was assumed to be Gaussian distribution and the probability distribution of the maximum value of impact pressures was assumed to be three kinds of distributions: the delta function and Gaussian and Weibull distributions. Two parameters in equations describing the distribution of impact pressure were estimated using Bayesian optimization by comparing the distribution of the cavitation damage obtained from the experiment with the distribution of the accumulated plastic strain obtained from the simulation. Regardless of the distribution type, the estimated maximum impact pressure was 1.2-2.9 GPa and existed in the range of values predicted by the ratio of the diameter and depth of the pit. The estimated dispersion of the impact pressure distribution was 1.0-1.7 μm and corresponded to the diameter of major pits. In the distribution of the pits described by the accumulated plastic strain, which was assumed in three cases, the delta function and Gaussian and Weibull distributions, the Weibull distribution agreed well with the experimental results, particularly including relatively large pit size. Furthermore, the Weibull distribution reproduced the depth profile, i.e., pit shape, better than that using the delta function or Gaussian distribution. It can be said that the cavitation erosion phenomenon is predictable by adopting the Weibull distribution. This prediction method is expected to be applied to predict the cavitation damage in fluid equipment such as pumps and fluid parts.

A novel quantitative measurement method for formation element via iterative support vector regression

Pulsed neutron sources provide notable advantages in well logging tools. They emit high-energy neutrons and can be controlled effectively. These emitted neutrons induce gamma rays, which can be detected and utilized to estimate diverse formation properties. One such application is the determination of elemental concentrations using gamma spectroscopy, enabling accurate characterization of mineralogy and total organic carbon in complex reservoirs. However, in field tests, the extraction of net inelastic energy spectra becomes challenging due to the diverse environment. Additionally, the measurement of actual gamma spectra is susceptible to the effects of formation conditions and detector performance, resulting in statistical errors and unavoidable noise within the measured gamma spectra. Consequently, the accuracy of elemental concentration estimation is reduced. To address these challenges, this paper proposes a novel method for accurately estimating formation elemental concentrations. Initially, the capture deduction coefficient is calculated by fitting the gamma time spectra iteratively, enabling the extraction of net inelastic gamma spectra in various formation environments. Subsequently, an iterative support vector regression (ISVR) method is proposed to obtain the stable and accurate non-negative elemental yields, even in the presence of gamma spectrum noise. Finally, the obtained elemental yields are converted to accurate elemental concentrations using the oxide closure model and pseudo-capture spectroscopy. The accuracy and robustness of proposed method are validated on simulated mixed spectra with high noise. Field test results are compared with core analysis results to assess the accuracy of the determined elemental concentrations.

DiffMod – statistical 2D simulation model of neutron propagation and moderation

DiffMod is a simulation program for the evolution of a neutron ensemble in a thermal target – moderator – reflector assembly of a pulsed neutron source based on the statistical description of diffusion, scattering, moderation, and absorption processes. The spatial resolution, the energy resolution and the diffusion directions are strongly restricted to achieve calculation times in a realistic moderator – reflector assembly below 1 hour. In comparison with Monte-Carlo simulations describing the geometry and interactions between neutrons and moderator material exactly, we prove that the DiffMod approach can deliver intensities and pulse shapes that are exact within 10% compared to the Monte-Carlo simulations that require much more computing power. In addition, a time-resolved illustration of the spatial distribution of the neutrons at different energy levels is provided.

Effect of anode shape on neutron and x-ray emission in dense plasma focus

The neutron and x-ray production is investigated in various pulse-power devices for a deeper understanding of the ion and electron acceleration mechanisms and the application of pulsed neutron sources. We present the extensive results from an anode shape experiment carried out on the PFZ-200 plasma focus device. The various shapes of anodes were tested, including cylinders, tapers, or rounded tips. The experimental shots with a peak current above 200 kA were performed in pure deuterium working gas at 280–600 Pa pressure to obtain maximal neutron yield for each anode shape. The average neutron yields are in the range of (1–2) ×108 neutrons/shot. Outstanding findings about x-ray emission were obtained with the group of tapered anode tips. Using the scintillation detectors shielded by 5 cm thick lead bricks, we obtained the hard x-ray signals with photons exceeding 600 keV energy. Such relatively high x-ray energy indicates the optimized conditions for electron and ion acceleration. At the same time, the individual shots have been well reproducible. Therefore, we were able to study plasma dynamics with the schlieren images taken at different times at different shots.

Prompt Radiation Dose Analysis Within the European Spallation Source Connection Cell

The European Spallation Source (ESS) is a pulsed spallation neutron source currently being built in Lund, Sweden. At full power and beam energy, ESS will accelerate protons to 2 GeV at 5 MW (average pulse current of 62.5 mA, pulse length of 2.86 ms, and repetition rate of 14 Hz) onto a rotating, helium-cooled, tungsten target. This target is in a heavily shielded structure referred to as the target monolith, which is located inside the ESS target building. Directly on top of the target monolith shielding is a room referred to as the connection cell, which contains many important utility connections and control systems. Many connections from components in the target monolith, e.g., cooling water and electrical connections, exit the monolith into the connection cell and pass through the walls of the connection cell to reach other areas of ESS. When the accelerator is operating at ESS, the connection cell will be off limits to humans. This paper evaluates the prompt dose rates to several important materials in the connection cell and suggests an algorithm for evaluating the suitability of materials that might be used in the connection cell.

On-line determination of the water cut and chlorine impurities in crude oil using a pulsed beam of fast neutrons

A neutron-based sensor has been developed able to measure the water cut and the chlorine content in crude oil. The sensor is based upon the use of a pulsed fast neutron source. Two different cases were studied. Case ‘‘A’’: chlorine detection with no water present and case ‘‘B’’: water cut measurements with no chlorine present. The minimum detection limits for case A and case B were found to be (62 ± 6) mg/L and (2 ± 2) vol%, respectively.