Neutron Science Research Articles

Use of LANSCE Spallation Neutrons to Drive a Fusion Prototypic Neutron Source

A high-power neutron-producing spallation source is one option for meeting the mission of a fusion prototypic neutron source (FPNS). The Los Alamos Neutron Science Center at Los Alamos National Laboratory is uniquely suited to host such a source. A target concept has been developed that satisfies the initial goals established for an FPNS, as has a beam transport design that satisfies beam-on-target requirements for the concept. We discuss the potential impact of pulsed beam operation on radiation-induced changes in microstructure, as well as the ingrowth of calcium in steel alloys at a rate well beyond that expected in a fusion reactor first wall. A preliminary thermomechanical assessment shows the need to modify the target design to reduce temperatures and stresses in the tungsten target.

Photon strength functions, level densities, and isomeric ratio in Er168 from the radiative neutron capture measured at the DANCE facility

Background: The statistical approach is usually applied for the description of electromagnetic decay of the nucleus with the exception of the lowest excitation energies as well as for the calculation of the interaction of photons with nuclei, in particular the reaction cross sections. This concept employs nuclear level density (NLD) and photon strength functions (PSFs).Purpose: While PSFs and NLD of some well-deformed rare-earth nuclei were measured by several methods, sometimes with conflicting results, the PSFs of $^{168}\mathrm{Er}$ were addressed only by $(\ensuremath{\gamma},{\ensuremath{\gamma}}^{\ensuremath{'}})$ experiments. On the other hand, the low-lying levels of $^{168}\mathrm{Er}$ are well studied, including the isomeric state at 1094 keV, which enables various tests of the statistical approach.Methods: The $\ensuremath{\gamma}$ rays following radiative neutron capture on a $^{167}\mathrm{Er}$ sample were measured with the highly segmented $\ensuremath{\gamma}$-ray calorimeter Detector for Advanced Neutron Capture Experiments at the Los Alamos Neutron Science Center. The $\ensuremath{\gamma}$-ray energy spectra for different multiplicities (multistep cascade, or MSC, spectra) were gathered for many $s$-wave resonances of both possible spins. Moreover, we were able to detect the decay of the short-lived isomer and deduce the isomeric ratio for a few resonances.Results: Analysis of the MSC spectra within the statistical model enabled us to draw conclusions about dipole PSFs, in particular on the properties of the scissors mode, and NLD. The spectra can be well reproduced with phenomenological PSFs models but not with any of several models based on quasiparticle random-phase approximation (QRPA) calculations with different interactions. We showed that nonstatistical effects in feeding of the isomeric state play a role up to excitation energies of at least about 2 MeV.Conclusions: Deduced parameters of the scissors mode were found to be similar to those of neighbor well-deformed even-even Gd and Dy nuclei. Models like that of Kadmenskij, Markushev, and Furman (KMF) or like the modified generalized Lorentzian (MGLO) model provide a good description of experimental spectra. In contrast to several previous analyses of well-deformed rare-earth isotopes, we were able to match the experimental isomeric ratio with statistical model simulations.

Comparison of Neutron Radiation Testing Approaches for a Complex SoC

Commercial Systems-on-a-Chip (SoC) have grown more abundant in recent years, including in space applications. This has led to the need to test SoCs in radiation environments, which is difficult due to their inherent complexity. In this work we present two complementary approaches to testing digital SoC devices—a bare metal approach and an operating system based approach—and discuss their advantages and disadvantages. Experimental data collected using these two methods in September 2021 from Los Alamos Neutron Science Center (LANSCE) on the Xilinx UltraScale+ MPSoC is presented and discussed.

Online learning to train users of muons and neutrons at ISIS

Online learning is being adopted across a wide range of disciplines, providing remote access to resources that serves to widen participation in training, and allowing courses to be created that are accessible to the diverse range of learning styles that have recently been identified. Online resources can also be used to supplement more traditional in-person training by bringing a cohort of learners up to a common minimum level beforehand, distributing materials during training, and reinforcing learning after the event. Over the last six years ISIS has developed a range of online learning materials about muon and neutron science, that can be used independently or in association with in-person training. Here we discuss the materials now available and how they were designed to work effectively, set out the opportunities and challenges of online training for facility users, and summarise planned future developments.

Advancements of the nSpec system

A new characterization of the detector response for the EJ301 liquid scintillator based nSpec system has been conducted at the Los Alamos Neutron Science Center. The new characterization was accomplished in two orders of magnitude less time and with better statistics than the previous characterization. The new and old characterization methods were compared by conducting both types of characterization on two detectors (one EJ301 and one EJ301D). The two methods show consistent results and compare well to results previously published in the literature; however, the results from the characterization of the original nSpec detector show discrepancies that have been identified as being caused by oxygen being absorbed into the detector due to a leak. The new characterized detector response shows improved spectrum unfolding performance than the previous characterization. The cross talk of the detector system was also characterized as a function of incident neutron energy and found to have a negligible impact on spectrum unfolding results.Alternative materials (EJ301D and stilbene) were also characterized in a first step towards an upgraded system. The different materials show little difference in unfolding performance, but the comparison is ongoing. A SiPM based stilbene detector was used to evaluate the use of SiPMs in a future system upgrade. The SiPM provides adequate performance, but the custom SiPM readout results in a much longer pulse width than PMT based systems. The measured light output of the SiPM based stilbene compares well with the results in literature. Future work will look at additional materials (deuterated stilbene and organic glass) and optimizing the SiPM readout to decrease the pulse width.

Editorial: European Conference on Neutron Scattering 2023 in Garching

This edition of the European Conference on Neutron Scattering, which is held every four years, took place in Garching, Germany and gathered over 500 people from all areas of neutron science. From new source or instrumental concepts to fundamental physics, and chemistry, all areas of this community were represented. Lively discussions in the lecture halls, poster areas,and social events around this conference contributed to a very fruitful exchange of new ideas.

The new Device for Indirect Capture Experiments on Radionuclides at LANSCE: Efforts on measuring the resonance(s) responsible for the extremely large 88Zr (n,γ) cross section

The thermal neutron capture cross section of 88Zr was recently reported to be the second largest in nature with the largest resonance integral measured. Presumably, these very large values are caused by a resonance or resonances very near thermal energy. Determining their energies and widths, and hence the shape of the cross section away from thermal energies,is useful for applications. The short half-life (83.4 days) and associated large background, renders direct measurements of the neutron capture cross section impossible using current techniques. However, it is possible to measure the total neutron cross section, and hence the resonance properties, using the newly commissioned Device for Indirect Capture Experiments on Radionuclides (DICER) at the Los Alamos Neutron Science Center (LANSCE). Transmission measurements are utilized as a surrogate method to perform capture measurements. The 88Zr needed for a DICER measurement was produced at the Isotope Production Facility (IPF) and cleanly separated from the production target material. A description of the new instrument, efforts and preliminary results on 88Zr will be presented.

The HERMES reflectometer at the JULIC Neutron Platform

HERMES is a time-of-flight reflectometer that operated at the Orphée reactor until 2019. In 2022, HERMES was installed at the JULIC (Jülich Light Ion Cyclotron) Neutron Platform as part of a collaboration between the Laboratoire Léon Brillouin and the Jülich Centre for Neutron Science. The main goal of the current setup is to probe the viability of neutron instrumentation at a High Current Compact Accelerator-driven Neutron Source (HiCANS). As the flux at the JULIC neutron platform is several orders of magnitude lower than the original Orphée flux or the expected flux for a HiCANS, our current objective is to perform reflectivity experiments with supermirrors as a proof of concept. Nevertheless, Monte-Carlo simulations showed that the HERMES instrument’s performance at a HiCANS such as HBS or ICONE could match that of reflectometry instruments operating at research reactors or spallation sources. An experiment with a supermirror carried out in December 2022 allowed us to preliminary prove the feasibility of this kind of experiments at an accelerator-driven neutron source.

New Capabilities of the RPI γ-Multiplicity Detector to Measure γ-Production

Accurate modeling of γ-production in neutron capture reactions is critical for many applications including on-proliferation, safeguards and modeling nuclear reactors. To improve this work, the Rensselaer Polytechnic Institute (RPI) 16-segment γ-multiplicity NaI(Tl) detector at the Gaerttner Linear Accelerator (LINAC) Center has been upgraded by implementing a digital data acquisition system. The new digitized system records the γ-energy deposition distribution in each individual detector, and γ-multiplicity values as a function of neutron time-of-flight (TOF). With the new capabilities, high precision capture (and fission) yield measurements can be made, and the accuracy of simulation tools used to predict capture γ-cascades can be tested. To validate the updated system, an experiment was performed using a natural Ta sample to measure 181Ta and 180mTa resonance capture yield by detecting prompt γ-rays emitted from neutron capture interactions as a function of both neutron energy and measured γ-multiplicity of each capture event. The results confirm earlier measurements and agree with theoretical yield in the low energy resonance region from 1 to 20 eV. A 238U(n, γ) measurement was also performed to generate γ-spectra. For capture γ-cascades where the total γ-energy deposition is close to the neutron binding energy, γ-spectra were measured for individual resonance energies and observed γ-multiplicities. The results are comparable in shape to a recent measurement done using the Detector for Advanced Neutron Capture Experiments (DANCE) array at Los Alamos Neutron Science Center (LANSCE); however, differences need to be compared to Monte-Carlo n-particle simulations.

Prompt fission neutron spectra in the 235U(n,f) reaction

Prompt fission neutron spectra (PFNS) are crucial to any neutronic simulation of critical nuclear systems. An experimental setup dedicated to the measurements of PFNS of very high accuracy was developed at the Los Alamos Neutron Science Center (LANSCE) some ten years ago. It allows for the measurement of PFNS for neutron induced fission at the Weapon Neutron Research (WNR) neutron source of the LANSCE. A measurement of the PFNS from the 235U(n,f) reaction was realized recently and is currently analyzed. Preliminary results are presented here and are compared to present nuclear data evaluations.

A steady state vs pulsed fusion neutron science facility

Two major modifications to the existing steady state fusion neutron science facility (FNSF) concept (Kessel et al 2018 Fusion Eng. Des. 135 236–70) are investigated with the aim of determining whether or not its predicted performance can be improved. The modifications are high magnetic field and pulsed operation. We find that high field leads to major economic improvements in a steady state FNSF, although at the expense of lowering the engineering gain. Pulsed operation replaces the problems associated with low current drive efficiency, with hopefully more manageable engineering problems. Here, however, high toroidal field (TF) is not helpful, and a lower TF field is more desirable economically. Pulsed FNSFs also have a reduced engineering gain. Further modifications lead to FNSF designs satisfying the additional constraint of engineering gain equal to unity. For these designs there is a large cost penalty for the steady state FNSF but only a modest penalty for the pulsed FNSF. All of our modified designs show modest to large potential economic improvements over the existing design. Overall, our conclusion is that it may be desirable to carry out a more detailed analysis of one of our improved designs, the choice depending upon which issue in the existing design is most important.

Experimental realization of neutron helical waves.

Methods of preparation and analysis of structured waves of light, electrons, and atoms have been advancing rapidly. Despite the proven power of neutrons for material characterization and studies of fundamental physics, neutron science has not been able to fully integrate these techniques because of small transverse coherence lengths, the relatively poor resolution of spatial detectors, and low fluence rates. Here, we demonstrate methods that are practical with the existing technologies and show the experimental achievement of neutron helical wavefronts that carry well-defined orbital angular momentum values. We discuss possible applications and extensions to spin-orbit correlations and material characterization techniques.

Evaluation of fault injection tools for reliability estimation of microprocessor-based embedded systems

Statistical fault injection is widely used to estimate the reliability of mission-critical microprocessor-based systems when exposed to radiation and to evaluate the performance of fault mitigation strategies. However, further research is needed to gain a better understanding of the accuracy of the results and the feasibility of their application under realistic radiation conditions. In this article, an understanding of scenarios in which Instruction Set Architecture simulators or emulators may be relied upon for realistic statistical fault injection campaigns is advanced. An analysis is presented of the results from two simulation-based fault injection tools versus a set of fault emulation results on a real processor. The conclusions of the analysis assist the selection of the most efficient tool and method for testing many different software-based fault mitigation techniques within reasonable time periods and at affordable costs throughout an irradiation campaign. In particular, it was established that a partially ordered set of relations could be defined on the basis of statistical fault injection in relation to the effects of different versions of an application and a given simulator that remained unaltered during the irradiation experiments. The tests were conducted with a Texas Instruments MSP430 microcontroller to perform both fault injection campaigns and irradiation experiments using neutrons at the Los Alamos Neutron Science Center (LANSCE) Weapons Neutron Research Facility at Los Alamos, USA.

Particle physics readout electronics and novel detector technologies for neutron science

Traditional thermal neutron detectors are based on Helium-3 as conversion and detection material due to its large neutron cross-section. The difficult availability of this converter and the simultaneous higher demand for neutron detectors lead to the investigation of alternatives. Solid converters with a large thermal cross-section as boron or gadolinium, which emit charged particles when hit by a neutron are a prominent type. Similar to the concepts in particle physics, the techniques then rely on charged particle detection. A prime example is the Gadolinium Gas Electron Multiplier (GdGEM) detector for the NMX instrument at ESS.We present three further novel concepts for neutron detectors. By modifying existing detector principles with a solid converter and employing recent high-granular readout electronics from particle physics we aim at developing thermal neutron detectors beyond the state-of-the-art. The first concept combines the Timepix3 data-driven, self-triggered readout chip with a boronated Micro-Channel Plate. The second concept is a Time Projection Chamber with boronated scintillator walls. The third concept combines boronated segmented GEMs with a VMM3a-based strip readout.This proceeding introduces the novel concepts, outlines how they could go beyond the state-of-the-art, sketches the current progress and obstacles overcome and, where available, presents first measurement results. The project, even though at an intermediate stage, shows the high value of technology transfer between disciplines and the originality required to start such a process.

PaNOSC – Making FAIR open data a reality for Photon and Neutron Science

PaNOSC – Making FAIR open data a reality for Photon and Neutron Science The Photon and Neutron Open Science Cloud (PaNOSC) is a European project enabling open science through the adoption of FAIR principles across photon and neutron (PaN) facilities in Europe. To this aim, PaNOSC has developed and provided common policies and software and services connected to and made accessible via the European Open Science Cloud (EOSC).

Progress in commissioning a neutron/X-ray radiography and tomography systems at IAEA NSIL

The Nuclear Science and Instrumentation Laboratory (NSIL) is currently establishing a Neutron Science Facility (NSF) based on two compact neutron generators: Deuterium-Deuterium (DD), resulting in 2.45 MeV neutrons, and Deuterium-Tritium (DT), resulting in 14.1 MeV neutrons, with maximum source intensities up to 5 × 106 n/s and 4 × 108 n/s over 4π, respectively. Neutron/X-ray radiography and tomography are two of the applications the NSF will be equipped with. In this paper, we report the state of the radiography and tomography system, and the neutron/X-ray radiography and tomography experiments we performed. Good radiographs and tomographs are obtained with X-ray. The spatial resolution of the X-ray radiography system is measured to be about 0.1 mm. The thermal neutron radiographs and fast neutron radiographs have proved that the DD neutron generator will be beneficial to demonstrate neutron radiography capabilities for educational purposes. Additionally, the detail of the collimator optimization of the DD neutron radiography was presented.

Implementation and validation of realistic (n, x) reaction yields in Geant4 utilizing a detailed evaluated nuclear reaction library below 20 MeV

Neutron-induced reactions with charged particle emission play an important role in a variety of research fields ranging from fundamental nuclear physics and nuclear astrophysics, to applications of nuclear technologies, to energy production, and material science. Recently, the capability to study reactions with radioactive targets has become important to significantly advance research in explosive nucleosynthesis and nuclear applications. To achieve the relevant research goals and study (n, x) reactions over a broad neutron beam energy range, the Low Energy Neutron-induced charged-particle (Z) chamber (LENZ) at Los Alamos Neutron Science Center (LANSCE) was developed, along with varied ancillary instrumentation, to enable the aforementioned research program. For the (n, x) reactions of interest at low energies, a precise simulation of the discrete spectrum of emitted charged particles is essential. In addition, since LANSCE is a user facility, a simulation of the LENZ setup easily accessible by users has a high value. With these goals in mind, we have developed a detailed simulation using the Geant4 toolkit. In this work, we present the implementation and the validation of the simulation using experimental data from recent campaigns with the LENZ apparatus. Specifically, we benchmark the simulation against a similar MCNP-based application, and determine the realistic range of applicability for the utilized probability biasing technique. We describe the implementation of an evaluated library with angular distribution and partial cross-section data, and we perform a validation of the simulation based on comparisons of simulated spectra with experimental ones for a number of targets used in previous experimental campaigns. Lastly, we discuss the limitations, caveats, and assets of the simulation code and techniques used.

6Li(n,t)α reaction event-identification for the 235U(n,f)/6Li(n,t) cross section ratio measurement in the NIFFTE fissionTPC

While nuclear data play an important role in nuclear physics applications, it has become important to have a better understanding of the data and try to minimize the uncertainties. In particular, there is a need for precision neutron-induced fission cross section measurements on fissile nuclei. Neutron-induced fission cross sections are typically measured as ratios, with a well-known standard in the denominator. While the 235U(n,f) reaction is a well measured standard, some light particle reactions are also well-known and their use as reference can provide information to remove shared systematic uncertainties that are present in an actinide-only ratio. A recent measurement of the 235U(n,f) reaction using as a reference the standard 6Li(n,t) reaction, was conducted at the Los Alamos Neutron Science Center using the NIFFTE collaboration’s fission time projection chamber (fissionTPC). The fissionTPC is a 2×2π charged particle tracker designed for measuring neutron-induced fission. Detailed 3D track reconstruction of the reaction products enables evaluation of systematic effects and corresponding uncertainties which are less directly accessible by other measurement techniques. This work focuses on the analysis for the event identification of the 6Li(n,t)α reaction in the fissionTPC.

A new approach for indirect capture measurements: The DICER neutron transmission station at LANSCE

Direct (n,γ) measurements on radioactive nuclei can often be challenging. Substantial effort has been devoted to developing indirect techniques and perform measurements on short-lived radionuclides of astrophysical interest. A new indirect technique is being explored at the Los Alamos Neutron Science Center (LANSCE) which enables the calculation of average neuron capture properties from neutron transmission data. A station for neutron transmission, has been under commissioning during the last two years at LANSCE. The Device for Indirect Capture Experiments on Radionuclides (DICER) is currently capable of carrying out measurements on stable cylindrical samples with a diameter as small as 1 mm and mass as low as a few mg. The first year of operation indicate that the DICER instrument is ready to perform its first measurement on a radioactive sample (88Zr, t1/2=83.4 days) which is planned for the winter of 2021. A brief description of the apparatus and details on the latest DICER results will be presented.

Constraining the nuclear spin distribution using improved ^{197}Au neutron resonance parameters

New neutron transmission data at resonance energies using a ^{197}Au sample were measured using an early version of the Device for Indirect Capture Experiments on Radionuclides (DICER), which is under development at the Los Alamos Neutron Science Center (LANSCE). These data were combined with previous neutron transmission and capture data in a simultaneous R-matrix analysis to extract improved neutron resonance parameters for this nuclide. As a result, total radiation widths, varGamma _{gamma }, were obtained for 33 J=1 and 44 J=2^{197}Au+n resonances. varGamma _{gamma } distributions for these two spins states were compared to distributions calculated according to the nuclear statistical model using published nuclear level density (NLD) and photon strength functions (PSF) measured using the Oslo technique. The calculated distributions were found to be narrower and the average values for the two spins states closer together than the data. The calculation can be brought into agreement with the data by substantial modifications to the spin distribution in ^{198}Au as a function of excitation energy. As far as we know, the spin distribution currently is otherwise poorly constrained. The modified spin distribution changes the shapes of the NLD and PSF extracted using the Oslo technique and so could have broad implications.