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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Incident beamline design for a modern cold triple axis spectrometer at the High Flux Isotope Reactor

A modern cold triple axis spectrometer is being planned for the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Here, we describe the design of an incident beamline that will put a flux of ~ 10 8 $\frac {n}{cm^{2}s}$ on a sample with an area of 2 cm X 2 cm. It takes current physical constraints at HFIR into account and it can accommodate both single and multiplexed analyzer-detector secondary spectrometers and large superconducting magnets. The proposed incident beamline includes a multi-channel guide with horizontal focusing, a neutron velocity selector, components to facilitate an incident beam polarization option, and a double-focusing pyrolytic graphite monochromator. Here, this work describes the process of optimizing the guide system and monochromator and summarizes the expected performance of the incident beamline for non-polarized operation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2026

Improvements in the Sample Space for the Backscattering Silicon Spectrometer (BASIS)

The increase in neutron flux at the Oak Ridge National Laboratory (ORNL) Spallation Neutron Source (SNS), currently operating at 2.0 MW proton beam power, has created new opportunities for higher-throughput neutron scattering experiments while also increasing the importance of minimizing background scattering and optimizing sample-environment operations. To address these challenges on the Backscattering Silicon Spectrometer (BA-SIS), several upgrades were developed and evaluated, including boron carbide (B₄C) masking for flat-plate sample containers, multi-cell sample holders used with a vertically translating sample stick, and an automated helium pump and purge (HPP) system for closed-cycle refrigerators. Neutron diffraction measurements demonstrate that B₄C masks reduce background scattering by 49–67%, outperforming both borated aluminum and boron nitride masks while introducing no additional Bragg reflections within the instrument’s accessible Q-range. Commissioning tests of a double-cell flat-plate sample contain-er showed no measurable crosstalk between adjacent sample compartments and con-firmed stable thermal performance, enabling multiple samples to be measured without re-peated temperature cycling. In addition, the automated HPP system provided reproducible sample-space gas handling with approximately ±1 mbar precision while reducing the need for operator intervention and supporting remote operation. Together, these developments improve signal-to-noise performance, increase experimental throughput, and enhance operational efficiency at BASIS, supporting the instrument’s continued operation under higher neutron flux conditions.

Jalarvo, Niina [ORNL] (ORCID:0000000306446866)↗
DOE OSTI2024

ZrH2 as measured on ARCS for NXS2021

This data is for ZrH2 in an Al can it is measured at room temperature. This data was used for the Neutron and Xray scattering school in 2021. It was measured on the ARCS direct geometry spectrometer at the spallation neutron source. The .nxs files are event files that can be read and processed with Mantid. The nxspe files are auto reduced files that can be read with Mantid, Dave, or Mslice. Both types of files are hdf5 and can be read with any tool that reads hdf5.

MATERIALS SCIENCE↗
DOE OSTI2026

A novel compact end-loaded piston cylinder cell for high pressure neutron scattering up to 5 GPa

Here, a miniature sized end-loaded piston cylinder cell with radial side windows for neutron scattering experiments is described. The principle of the bicone-shaped cylinders used was first presented by McWhan in 1974. The present cell is of compact portable design yet significantly enlarges the scattering angles. Its small size allows neutron scattering experiments at low temperatures. The bicone-shaped cylinders are made from various ceramics or a highly neutron-transmissive Ni-free Cr–Mo–V steel. Successful neutron scattering experiments up to 5 GPa have been demonstrated on the CORELLI single-crystal diffractometer and the VISION vibrational spectrometer of the Spallation Neutron Source at the Oak Ridge National Laboratory.

Neutrons↗
DOE OSTI2024

First measurement in a magnetic confinement fusion experiment of the H 3 + H 3 → He 5 + n intermediate two-body resonant reaction

We report on the first experimental measurements made at a magnetic confinement fusion device of the tritium(T)-tritium(T) reaction T + T → He 4 + 2 n indicating the presence of the intermediate two-body resonant reaction T + T → He 5 + n . During the second deuterium-tritium campaign (DTE2) at the Joint European Torus, measurements of fusion plasmas with high tritium concentrations, n T / ( n T + n D ) ≈ 0.99 , heated with tritium neutral beam injection, were performed using the neutron time-of-flight (TOF) spectrometer TOFOR. We detect a peak in the neutron emission TOF spectrum consistent with the two-body resonant reaction. The TT neutron emission energy spectrum is modeled using an R -matrix framework where the distributions of the most likely model parameters given our experimental TOF data are determined utilizing a Markov chain Monte Carlo approach. We compare our best estimate of the T + T neutron emission energy spectrum with results obtained at inertial confinement fusion experiments at the OMEGA facility and find a spectral shape that is consistent with the energy dependency in the neutron spectrum observed at OMEGA. Published by the American Physical Society 2024

Physics↗
DOE OSTI2021

H 2 production in the 10 B(n,α) 7 Li reaction in water

Herein we demonstrate a method for measuring the H2 produced in water from the 10 B(n,α) 7 Li fission reaction. Low energy neutrons from the NIST Center for Neutron Research interact with borate-containing water in a temperature-controlled high pressure cell made from titanium. After exposure for one to several hours, the water is extracted and sparged with argon. H 2 entrained in the sparging gas is sampled with a small mass spectrometer. To determine the neutron exposure, a small amount of sodium is included in the borate solution. The water is collected and 24 Na activation is measured in a counting apparatus on the following day. The G-value for H 2 at room temperature is found to be (1.18 ± 0.10) molecules H 2 /100eV, in good agreement with previous estimates and recent modeling calculations.

10B↗
DOE OSTI2023

H 2 generation by the 10 B(n,α) 7 Li reaction in high temperature water

H 2 produced in water from the 10 B(n,α) 7 Li fission reaction has been measured up to 300 °C. Thermal energy neutrons from the Rhode Island Nuclear Science Center's 2 MW reactor interact with boric acid-containing water in temperature-controlled high-pressure cells made from tubing of either titanium or zirconium alloy. After exposure for a minimum of 1 h, the solution sample is extracted and sparged with argon. The H 2 entrained by the sparging gas is sampled with a small mass spectrometer. A small amount of sodium is included in the boric acid solution so that after sparging, samples can be collected for 24 Na activation measurements in a gamma spectrometer to determine the neutron exposure and thus the total energy deposited in solution. The G-value (μmol/J) for H 2 production is obtained for water at a pressure of 25 MPa, over a temperature range from 20 °C to 300 °C. The weak temperature dependence of this yield between 150 °C and 200 °C demonstrates that the bimolecular reaction of pairs of e$^{–}_{aq}$ is a very minor source of H 2 in high LET tracks.

10B↗
DOE OSTI2020

Design and performance of a superconducting neutron resonance spin flipper

Despite the challenges, neutron resonance spin echo still holds the promise to improve upon neutron spin echo for the measurement of slow dynamics in materials. We present a bootstrap, radio frequency neutron spin flipper using high temperature superconducting technology capable of flipping neutron spin with either nonadiabatic or adiabatic modes. A frequency of 2 MHz has been achieved, which would achieve an effective field integral of 0.35 T m for a meter of separation in a neutron resonance spin echo spectrometer at the current device specifications. In bootstrap mode, the self-cancellation of Larmor phase aberrations can be achieved with the appropriate selection of the polarity of the gradient coils.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Measurement of the Neutron Electromagnetic Form Factor Ratio at High Momentum Transfer

The inner structure of the nucleon (proton and neutron) remains a topic of great interest in nuclear and particle physics, after many decades of study. For example, understanding the quark-gluon dynamics inside the nucleon would shed light on how 99% of the nucleon mass is created. The neutron electromagnetic form factors, Gn E and Gn M , give important insights into the neutron structure. The Super BigBite Spectrometer (SBS) program at Jefferson Lab (JLab) seeks to extend the form factor measurements for both the proton and the neutron. The neutron electric form actor, Gn E , has been historically difficult to measure due to the short lifetime of the free neutron and the small value of Gn E . The GEn-II experiment is part of the SBS program and seeks to measure Gn E , significantly increasing the high momentum transfer coverage. A newly designed polarized 3He target increased the figure of merit by three times compared to previous measurements. The analysis of this data is especially challenging due to the unprecedented high-rate environment caused by the open nature of the spectrometer with a direct line of sight to the target. This required developing new Gas Electron Multiplier (GEM) particle trackers which can cover large areas demanded by this setup and handle particle rates up to 500 kHz/cm2. Rates this high over a large area is unprecedented in particle tracking systems and came with a number of challenges. Data taken in the SBS program was critical to understanding hardware and software solutions that improved the track reconstruction efficiency to be >97% with a position resolution of 70 ?m. In previous experiments the proton electromagnetic form factors, Gp E and Gp M were measured up to Q2 = 8.5 GeV2 and Q2 = 30 GeV2, respectively, while Gn E has only been measured up to Q2 = 3.4 GeV2. The GEn-II experiment has measured the neutron form factor ratio, Gn E/Gn M, at Q2 values of 2.90, 6.50, and 9.47 GeV2 by scattering a polarized electron beam with a polarized 3He target, used here as an effective polarized neutron target, and measuring the double spin asymmetry of the cross section. Previous Gn E measurements do not extend above Q2 = 3.4 GeV2, and therefore this analysis has extended the world data by almost three times. The background correction is especially difficult at the higher Q2 settings leading to large systematic errors. As very exploratory results from this early analysis of the data, we find for Q2 = 2.90 GeV2, Gn E = 0.0157 ±stat 0.0016 ±sys 0.0011, for Q2 = 6.50 GeV2, Gn E = 0.0067 ±stat 0.0019 ±sys 0.0005, and for Q2 = 9.46 GeV2, Gn E = 0.0046 ±stat 0.0023 ±sys 0.0005. These results are compared to predictions from the Dyson-Schwinger Equations (DSE) model and a Relativistic Constituent Quark Model (RCQM).

Jeffas, Sean↗
DOE OSTI2023

Investigation of the Role of the Role of Nuclear Physics in Heavy Element Nucleosynthesis, through the Study of Key Reactions, and the Improvement of Theoretical Reaction Rates (Final Report)

Neutrino-driven winds in core-collapse supernovae have been identified as a possible site for the production of elements heavier than iron. Traditionally, these neutrino-driven winds have been proposed as the site of the main r-process. Recent simulations fail to reproduce the conditions required for the main r-process. while they remain a promising site for producing the lightest elements beyond iron, e.g., Sr, Y, and Zr through the νp process. The efficiency of the νp process depends on the hydrodynamical conditions, the electron fraction (which is related to the neutrino properties), and the nuclear reactions on many short-lived nuclei with limited (if at all) experimental information. The reaction rates on these nuclei are based on theoretical predictions using the Hauser-Feshbach model. Recent sensitivity studies have highlighted the importance of neutron-induced reactions on these nuclei along the νp process path. This work aimed to experimentally constrain reaction rates that are known to play a key role in the neutrino-p process nucleosynthesis. A secondary subsequently-added objective was to start the implementation of techniques that improve the description of nuclear properties in the Hauser-Feshbach model by extending the microscopic nuclear level density description offered via the shell model to high excitation energies without using experiment-based renormalizations. The main objective of this work was the experimental constraint of the 56 Ni(n,p) 56 Co reaction rate via a measurement of the inverse reaction 56 Co(p,n) 56 Ni at the National Superconducting Cyclotron Laboratory (NSCL) and later the Facility for Rare Isotope Beams (FRIB). This reaction is considered the key one for determining the yields possible by the neutrino-p process. A technique for this type of measurement in inverse kinematics at low energies did not exist before this work. The work also had two secondary objectives. First, to contribute to efforts to measure the same reaction in direct kinematics using a radioactive target at Los Alamos National Laboratory (LANL), and second, to advance work to implement shell-model-deduced microscopic level densities in Hauser-Feshbach calculations. The project has resulted in the development of the first technique to perform (p,n) cross-section measurements in relevant-for-astrophysics low energies in inverse kinematics using a magnetic spectrometer or separator, and neutron detectors for neutron tagging. It has also resulted in the precise measurement of the cross-section of the 40 Ar(p,n) 40 K reaction in a proof-of-principle experiment realized by using a beam-line quadrupole of the ReA3 accelerator of NSCL/FRIB. As part of this project the technique was successfully adapted to make use of the superior acceptance of the Separator for Capture Reactions (SECAR) at FRIB. In this project, the required experimental setup simulations and beam optics were developed and tested with the measurement of the 58 Fe(p,n) 58 Cu reaction cross-section. Additionally, this project contributed with simulation work to the development of a technique to measure (n,p) reactions with radioactive targets at LANL, and which resulted in the measurement of the key 56 Ni(n,p) 56 Co reaction cross-section at neutron energies above ≈1 MeV. Last, the project initiated work in the development of shell model based level densities using the moments method.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Characterization of 244 Cm Neutron Sources

There is a need to find a replacement for the 252 Cf sources currently used in Standards-based performance testing of neutron instrumentation. This is a result of its relatively short half-life, concerns about future availability and recent increases in cost. A potential replacement source, 244 Cm is evaluated in this study where two commercially available sources have been acquired and their neutron emission spectra measured using a pair of spectrometers. Both instruments showed the 244 Cm spontaneous neutron spectrum to be fully consistent with a MCNP6®-calculated spectrum using published Watt fission parameters for 244 Cm. In addition, the emission rate of the weaker 244 Cm source was established through a direct count rate comparison against a calibrated and similarly encapsulated 252 Cf source. The 244 Cm source emission rate was found to be in excellent agreement with value stated on the manufacturer's source certificate. It is concluded that 244 Cm would be an ideal replacement for 252 Cf based on its longer half-life (18.1 y) and its essentially identical neutron emission spectrum. In addition, 244 Cm sources are commercially available at reasonable cost.

244Cm↗
DOE OSTI2021

Spatiotemporal mapping of mesoscopic liquid dynamics

The study of liquid dynamics at mesoscopic scales is still strewn with difficulty due to limitations in theory and experiment. Historically, significant attention has been given to the analysis of space-time correlation functions and their frequency-Fourier transforms at a few discrete wave numbers. The massive computing power afforded by modern high performance computing clusters and the advent of a wide-angle neutron spin-echo spectrometer, however, have unlocked a more intuitive and fruitful approach to this problem. Using molecular dynamics simulations, here we demonstrate the benefits of spatiotemporally mapping intermediate scattering functions on a dense grid of correlation times and wave numbers. Four model systems are investigated: a Lennard-Jones liquid, a coarse-grained bead-spring polymer, a molten sodium chloride, and a poly(ethylene oxide) melt. We show that the spatiotemporal mapping approach is particularly useful for elucidating the mesoscopic dynamics in these liquids, where several underlying mechanisms, such as molecular relaxations, hydrodynamic modes, and nonhydrodynamic excitations, are potentially at play. Therefore, compared to the traditional method, direct visualization of density space-time correlation functions on two-dimensional color maps permits appraisals of complicated dynamical behavior at mesoscales in a global manner. For example, the scaling relations between space and time for different types of molecular motions can be straightforwardly identified on these plots, without any model-dependent analysis. Additionally, we show how theoretical ideas regarding collective mesoscopic dynamics, such as the classical hydrodynamic theory, the convolution approximation, and a recently proposed phenomenological model, can be discussed in terms of the global features of spatiotemporal maps of intermediate scattering functions. The new perspective offered by the spatiotemporal mapping method should prove useful for the study of liquid dynamics in general.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Improved Chopper System for a Direct Geometry Spectrometer at the Second Target Station

This report describes a chopper cascade suitable for a cold direct geometry spectrometer at a pulsed neutron source with a low repetition rate such as the Second Target Station (STS) currently being planned at Oak Ridge National Laboratory (ORNL). The chopper cascade offers the following capabilities: selection of a variable number of pulses per frame (flexible pulse suppression), selection of pulses with increasing timing separation within one frame, and an increasing pulse width ∆t within one frame, in order to achieve an even energy resolution over several pulses at different wavelengths across the frame.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Absolute mass calibration of fission product distributions measured with the E-$v$ method

The mass calibration of fission product distributions measured with the energy–velocity (E-v) method constitutes a technical challenge. The energy loss of the fission fragments in the various dead layers of the spectrometer and other sources of pulse-height defects of the energy detectors are a significant source of systematic uncertainty in the mass calculations used to determine the measured fission product yields. Here, in this study, the absolute calibration of the fission mass distributions is accomplished by measuring prompt γ-rays in coincidence with the fission fragments. This allows for the direct calibration of the mass spectra and eliminates any dependence on potentially complicated energy corrections. The first test measurement was performed at the Los Alamos Neutron Science Center employing the SPectrometer for Ion DEtermination in fission Research (SPIDER). SPIDER is a 2E-2v spectrometer designed for measuring independent fission product yields from neutron-induced fission. In this test, the single-arm SPIDER (E-v) system and an array of 252 Cf sources were used. The single-arm system consisted of two time pick-off detectors for measuring the time-of-flight of the fission fragments and a double-sided silicon strip detector (DSSD) for measuring the kinetic energy. Characteristic γ-rays from fission fragments were detected using three high-purity germanium (HPGe) detectors. For the mass calibration, γ–mass coincidence events from twelve product isotopes were used. The measured FPYs from 252 Cf spontaneous fission were found to be in excellent agreement with the evaluated data after applying the absolute mass calibration. From the γ–mass coincidence events, the mass resolution of the system was also extracted. An average mass resolution of ~1.4 AMU (FWHM) for the light fragments and ~2.4 AMU (FWHM) for the heavy fragments were found. This was the first in-situ calibration and characterization of the SPIDER spectrometer, which paves the way for high-quality FPY measurements with this instrument.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Spectator Proton Detection and Reconstruction in Deep Inelastic D(E,EPS) Scattering

A Radial Time Projection Chamber (RTPC) was designed and installed in Jefferson Lab's Hall B as part of the BONuS12 (Barely Off-shell Nucleon Structure) experiment. The goal of BONuS12 is to accurately measure the structure function of the neutron by scattering 11 GeV electrons and detecting them with the CLAS12 spectrometer. Deuterium gas was used as an effective neutron target, and the new RTPC was used to detect low momentum spectator protons. Protons follow a curved path in the 5 Tesla solenoid that is part of CLAS12, ionizing the He-CO2 gas in an annular drift region surrounding the target. These ionization electrons are radially drifted outwards, amplified using cylindrical GEM (Gaseous Electron Multiplication) foils and recorded using readout pads located along the entire outer face of the cylindrical detector. The particle track reconstruction software discussed in detail in this thesis uses the signals from these pads to build tracks, which are reconstructed into the drift region using the arrival times of the signals and the positions of the pads. The proton momentum is measured from the track?s curvature and thus used to extract information about the struck neutron. This thesis introduces the theory of spectator tagging as an effective strategy for measuring neutron structure, by minimizing nuclear effects in the absence of a free neutron target. Along with discussing the many detectors that make up the CLAS12 spectrometer, the RTPC will be covered in detail, along with the tracking software designed to interpret the electronic signals to rebuild the low-momentum particle tracks, and fit them to extract the relevant kinematics. The results of the software, and preliminary analysis will be shown in the final chapter, as well as the discussion of possible improvements which could be made to the tracking software.

Payette, David↗
DOE OSTI2024

Decay studies of the 𝛽-delayed neutron emitters 87 Br and 88 Br measured by means of the Modular Total Absorption Spectrometer at ORNL HRIBF

The β decays of 87 Br, 88 Br, and 87 Kr were measured with the Modular Total Absorption Spectrometer (MTAS) at Oak Ridge National Laboratory’s Holifield Radioactive Ion Beam Facility (HRIBF). Both bromine isotopes are β-delayed neutron emitters that have large cumulative fission yields and were identified as top-priority cases for total absorption study by the Nuclear Energy Agency in 2007. Our investigations corroborate that the decay schemes of 87 Br and 88 Br suffer from the so-called pandemonium effect. Unique MTAS properties enable direct neutron measurements. Here, we present MTAS-derived β-delayed neutron spectra, β-delayed neutron emission probabilities of P n ( 87 Br) = 2.36(24)%, and P n ( 88 Br) = 6.4(6)%, and the β-delayed neutron transitions intensity of 4(2)% to the first excited 87 Kr state, populated in the β-neutron decay of 88Br. Incorporating new data into calculations of the electromagnetic decay heat component emitted during thermal neutron fission of 235 U and 239 Pu improves agreement with experimental data up to approximately 80 s after fission. The estimation of the nuclear reactor $\bar{ν}_e$ flux results in changes of up to 1% in the expected $\bar{ν}_e$ interactions with the detector material for 235 U, 238 U, 239Pu, and 241 Pu.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Second gadolinium loading to Super-Kamiokande

The first loading of gadolinium (Gd) into Super-Kamiokande in 2020 was successful, and the neutron capture efficiency on Gd reached 50%. To further increase the Gd neutron capture efficiency to 75%, 26.1 tons of Gd 2 (SO 4 ) 3 ∙ 8H 2 O was additionally loaded into Super-Kamiokande (SK) from May 31 to July 4, 2022. As the amount of loaded Gd 2 (SO 4 ) 3 ∙ 8H 2 O was doubled compared to the first loading, the capacity of the powder dissolving system was doubled. We also developed new batches of gadolinium sulfate with even further reduced radioactive impurities. In addition, a more efficient screening method was devised and implemented to evaluate these new batches of Gd 2 (SO 4 ) 3 ∙ 8H 2 O. Following the second loading, the Gd concentration in SK was measured to be 333.5 ± 2.5 ppm via an Atomic Absorption Spectrometer (AAS). From the mean neutron capture time constant of neutrons from an Am/Be calibration source, the Gd concentration was independently measured to be 332.7 ± 6.8(sys.) ± 1.1(stat.) ppm, consistent with the AAS result. Furthermore, during the loading the Gd concentration was monitored continually using the capture time constant of each spallation neutron produced by cosmic-ray muons, and the final neutron capture efficiency was shown to become 1.5 times higher than that of the first loaded phase, as expected.

Gadolinium↗
DOE OSTI2022

The ultrafast pixel array camera system and its applications in high energy density physics

Diagnostics in high energy density physics, shock physics, and related fields are primarily driven by a need to record rapidly time-evolving signals in single-shot events. These measurements are often limited by channel count and signal degradation issues on cable links between the detector and digitizer. Here we present the Ultrafast Pixel Array Camera (UPAC), a compact and flexible detector readout system with 32 waveform-recording channels at up to 10 Gsample/s and 1.8 GHz analog bandwidth. The compact footprint allows the UPAC to be directly embedded in the detector environment. A key enabling technology is the PSEC4A chip, an eight-channel switch-capacitor array sampling device with up to 1056 samples/channel. The UPAC system includes a high-density input connector that can plug directly into an application-specific detector board, programmable control, and serial readout, with less than 5 W of power consumption in full operation. We present the UPAC design and characterization, including a measured timing resolution of ~20 ps or better on acquisitions of sub-nanosecond pulses with minimal system calibrations. Example applications of the UPAC are also shown to demonstrate operation of a solid-state streak camera, an ultrafast imaging array, and a neutron time-of-flight spectrometer.

47 OTHER INSTRUMENTATION↗