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One crucial issue for the application of scintillation crystals in future high-energy physics experiments is radiation damage in a severe radiation environment, such as the high luminosity large hadron collider. While radiation damage induced by ionization dose in inorganic scintillators is well understood, investigations are ongoing to understand radiation damage induced by hadrons, including both charged hadrons and neutrons. Aiming at understanding neutron-induced radiation damage in fast inorganic scintillators, lutetium yttrium oxyorthosilicate (LYSO)/lutetium fine silicate (LFS), BaF2, and PWO crystals were irradiated at Los Alamos Neutron Science Center by a combination of particles, including neutrons, protons, and $\gamma $ -rays. The results indicate that LYSO/LFS and BaF2 crystal plates are radiation hard up to a 1-MeV equivalent neutrons fluence of $9 \times 10^{15}$ equivalent neutron (neq)/cm2, but not PWO, and the neutron-induced radiation damage in LYSO crystals is a factor of ten less than protons.

Background: Fast-neutron-induced reactions can be used to characterize reaction mechanisms, investigate nuclear structure, and impose constraints on nuclear models. Because of the difficulty in predicting such effects, experimental data are important to constrain models. Thallium isotopes located close to the doubly magic $^{208}\mathrm{Pb}$ nucleus are important for comparison with shell-model calculations.Purpose: Study the population of excited states in $^{203}\mathrm{Tl}$ and lighter isotopes in such reactions.Methods: $\ensuremath{\gamma}$-ray cross sections were measured. The data were taken by using the Germanium Array for Neutron-Induced Excitations spectrometer. The pulsed neutron source of the Los Alamos Neutron Science Center's Weapons Neutron Research facility provided neutrons in the energy range from 1 to 300 MeV. The time-of-flight technique was used to determine the incident neutron energies.Results: Cross sections for emission of several $\ensuremath{\gamma}$ rays in 20 reaction channels were determined. Candidates for the intruder $9/{2}^{\ensuremath{-}}$ state in $^{203}\mathrm{Tl}$, from the odd proton in the ${h}_{9/2}$ orbital, and the first ${5}^{+}$ states in $^{202,204}\mathrm{Tl}$, from admixture of configurations, were identified.Conclusions:The excitation energy of the candidate $9/{2}^{\ensuremath{-}}, \ensuremath{\pi}{h}_{9/2}$ state is in good agreement with the theoretical prediction from a semi-empirical weak-coupling model and its half-life is in the range of tens of nanoseconds. The feeding of a previously known isomer in $^{202}\mathrm{Tl}$ exhibits similarities with the feeding of other isomers in this mass region.

Future high-energy physics experiments at the energy and intensity frontiers will face a challenge of severe radiation environment from both ionization dose and charged and neutral hadrons. The high-luminosity large hadron collider, for example, will present an environment, where up to 130 Mrad ionization dose, $3 \times 10^{14}$ charged hadrons/cm2 and $5 \times 10^{15}$ neutrons/cm2 are expected. In this paper, we report our investigation on charged hadron-induced radiation damage in BaF2, LYSO/LFS, and PWO crystals up to $3 \times 10^{15}$ protons/cm2 by using 800-MeV protons at the Los Alamos Neutron Science Center. Comparison is made between radiation damages induced by protons and ionization dose alone.

Radiation hard diagnostics are critical to the success of nuclear fusion at National Ignition Facility, Z, ITER, and prolonged space explorations. We have first demonstrated the exceptional proton radiation hardness of initial GaN devices and qualified their space flight and deployment for missions such as the Laser Interferometer Space Antenna and International Space Station. We have further conducted neutron radiation hardness experiments at Los Alamos Neutron Science Center by opening a new high fluence beam station. During 2014–2016, we irradiated multiple Aluminum Gallium Nitride (AlGaN) LEDs with a maximum fluence of 2.4 × 1013 neutrons/cm2 in 3 years and generated 54 161 current–voltage (I–V) scan traces. Our data processing program analyzes each and all I–V traces. In addition, we retrieved local temperature records to analyze and remove temperature effects in the outdoor environment. The I–V curve families of AlGaN UV LEDs with emitting wavelengths of 265, 275, and 310 nm were compared. The I–V curves of 265 nm AlGaN UV LEDs have the smallest deviations from the average value, while the I–V curves for 310 nm AlGaN LEDs showed the largest deviations from the average value. We have reached another important recommendation for the optimal use of multiple AlGaN optoelectronic devices or imaging arrays for inertially confined fusion diagnostics: Shorter wavelength devices at 265 nm exhibit more consistent radiation hardness performance than the 310 nm devices. Higher aluminum content LEDs or AlxGa1–xN devices with higher mole fraction x for generating shorter wavelengths have better radiation hardness for fusion diagnostics.

This paper reports proton-induced radiation damage in fast crystal scintillators. Large size LYSO and CeF3 crystals of 20 and 15 cm long were irradiated by 800 MeV protons at Los Alamos up to $3.3\times 10^{14}$ p/cm2 with degradation and recovery of their longitudinal transmittance measured in situ . LYSO plates of $14\times 14\times 1.5$ mm3 were irradiated by 67 MeV protons at UC Davis up to $9.5\times 10^{13}$ p/cm2, and by 24 GeV protons at CERN up to $6.9\times 10^{15}$ p/cm2. The results show an excellent radiation hardness of LYSO crystals against charged hadrons.

One crucial issue for applications of inorganic scintillators in future HEP experiments is radiation damage in a severe radiation environment, such as the HL-LHC. While radiation damage induced by ionization dose is well understood, investigations are on-going to understand radiation damage induced by hadrons, including both charged hadrons and neutrons. Aiming at understanding neutron induced radiation damage in fast inorganic scintillators, BaF_2, LYSO/LFS and PWO crystals were irradiated at LANSCE by a combination of particles, including neutrons, protons and γ-rays. The results indicate that LYSO/LFS and BaF_2 crystal plates are radiation hard up to 4 × 10^(15) fast neutrons/cm^2.

A corrected description of the interpolation scheme for the neutron data standards is given. It is emphasized that the energies (nodes) listed are where the evaluated cross sections are shown. A numerical example that shows how the high-resolution 235U(n,f) data should be averaged to be compared with lower resolution cross sections is given.

Experiments searching for neutrinoless double $\ensuremath{\beta}$ decay ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) require precise energy calibration and extremely low backgrounds. One of the most popular isotopes for $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ experiments is $^{136}\mathrm{Xe}$. In support of these experiments, the neutron inelastic scattering properties of this isotope have been measured at the GErmanium Array for Neutron Induced Excitations (GEANIE) at the Los Alamos Neutron Science Center. Time-of-flight techniques are utilized with high-purity germanium detectors to search for inelastic scattering $\ensuremath{\gamma}$ rays for neutron energies between 0.7 and 100 MeV. Limits are set on production of yet-unobserved $\ensuremath{\gamma}$ rays in the energy range critical for $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ studies, and measurements are made of multiple $\ensuremath{\gamma}$-ray production cross sections. In particular, we have measured the production of the 1313 keV $\ensuremath{\gamma}$ ray, which comes from the transition of the first-excited to ground state of $^{136}\mathrm{Xe}$. This neutron-induced $\ensuremath{\gamma}$ line may be useful for a novel energy calibration technique, described in this paper.

This paper reports proton induced radiation damage in fast crystal scintillators . A 20 cm long LYSO crystal, a 15 cm long CeF3 crystal and four liquid scintillator based sealed quartz capillaries were irradiated by 800 MeV protons at Los Alamos up to 3.3 × 10 14 p / cm 2 . Four 1.5 mm thick LYSO plates were irradiated by 24 GeV protons at CERN up to 6.9 × 10 15 p / cm 2 . The results show an excellent radiation hardness of LYSO crystals against charged hadrons .

New data on the prompt fission neutron spectra (PFNS) from neutron-induced fission with higher accuracies are needed to resolve discrepancies in the literature and to address gaps in the experimental data. The Chi-Nu project, conducted jointly by LANL and LLNL, aims to measure the shape of the PFNS for fission of 239Pu induced by neutrons from 0.5 to 20 MeV with accuracies of 3–5% in the outgoing energy from 0.1 to 9 MeV and 15% from 9 to 12 MeV and to provide detailed experimental uncertainties. Neutrons from the WNR/LANSCE neutron source are being used to induce fission in a Parallel-Plate Avalanche Counter (PPAC). Two arrays of neutron detectors are used to cover the energy range of neutrons emitted promptly in the fission process. Challenges for the present experiment include background reduction, use of 239Pu in a PPAC, and understanding neutron detector response. Achieving the target accuracies requires the understanding of many systematic uncertainties. The status and plans for the future will be presented.

The Chi-Nu project, conducted jointly by LANL and LLNL, aims to measure the shape of the prompt fission neutron spectrum (PFNS) for fission of 239Pu induced by neutrons from 50 keV to 15 MeV with accuracies of 3–5% in the outgoing energy from 50 keV to 9 MeV and 15% from 9 to 15 MeV. In order to meet this goal, detailed Monte Carlo simulations are being used to assess the importance and effect of every component in the experimental configuration. As part of this effort, we have also simulated some past PFNS measurements to identify possible sources of systematic error. We find that multiple scattering plays an important role in the target geometry, collimators, and detector response and that past experiments probably underestimated the extent of this effect.

The capabilities of 7 Li-enriched Cs 2 7 LiYCl 6 (C 7 LYC) scintillation detectors for fast neutron spectroscopy are explored in benchmark experiments that exploit its excellent pulse-shape discrimination between neutrons and γ rays, and its unprecedented ≈ 10% energy resolution for fast neutrons in the few MeV range, obtained through the 35 Cl(n,p) reaction. Energy- and angle-resolved elastic and inelastic neutron scattering cross-section measurements of 56 Fe(n,n’) were performed at Los Alamos National Laboratory with a pulsed white neutron source and an array of 1 ″ × 1 ″ C 7 LYC crystals. The results convincingly establish the utility of this dual n/ γ scintillator for fast neutron spectroscopy. Intrinsic efficiency measurements of both 1 ″ × 1 ″ and the first ever 3 ″ × 3 ″ C 7 LYC crystal have been initiated, using mono-energetic fast neutron beams at UMass Lowell generated via the 7 Li(p,n) reaction. The spectroscopic capabilities and potential of C 7 LYC are discussed in the context of developing this emerging scintillator for targeted science applications.

New half-life measurements have been made of the millisecond isomers 71 m Ge, 114 m 2 I, 208 m Bi, 88 m 1 Y, 88 m 2 Y, and 75 m As populated in neutron-induced reactions. These measurements were made using the unique time structure of the LANSCE/WNR neutron source, by observing the γ -ray decays of the isomers during the time between the LANSCE proton macropulses. Two different LANSCE proton beam time structures were used. The GEANIE array of HPGe detectors was used to detect the γ -ray decays.

Absolute partial cross sections for production of discrete γ-rays using 60Ni( n , x n y p z α γ ) reactions with x ≤ 3 , y ≤ 2 and z ≤ 4 in a total of 20 reaction channels were measured. The data were taken using the GEANIE spectrometer comprised of 20 high-purity Ge detectors with BGO escape-suppression shields. The broad-spectrum pulsed neutron beam of the Los Alamos Neutron Science Center's (LANSCE) WNR facility provided neutrons in the energy range from 0.2 to 300 MeV. The time-of-flight technique was used to determine the incident neutron energies. Partial γ-ray cross sections have been measured for a total of 59 transitions and for neutron energies 1 MeV E n 300 MeV. Hauser-Feshbach theoretical calculations with an improved cluster emission model in the pre-equilibrium process were performed up to E n = 30 MeV and are compared to the experimental results.

A new neutron counter for research experiments on nuclear fission has been developed. This instrument is designed for the detection of prompt fission neutrons within relatively high levels of gamma and neutron background. It is composed of a set of 3He proportional counters arranged within a block of polyethylene which serves as moderator. The detection properties have been studied by means of Monte Carlo simulations and experiments with radioactive sources. These properties are confirmed by an experiment on neutron-induced fission of 238U at the WNR facility of the Los Alamos Neutron Science Center during which the mean prompt fission neutron multiplicity, or ν ¯ has been measured from 1 to 20 MeV of incident neutron energy.

The prompt neutron spectrum from neutron-induced fission needs to be known in designing new fast reactors, predicting criticality for safety analyses, and developing techniques for global security application. A program to measure this spectrum for neutron-induced fission of 239 Pu is underway at the Los Alamos Neutron Science Center. The goal is to obtain data on the shape of the spectrum with a small uncertainty over the emitted neutron energy range of 100 keV to 12 MeV with additional data below and above this range. The incident neutron energy range will be from 0.5 to 30 MeV. The status of this program including results of initial experimental measurements is described here.

The prompt γ-ray spectra from 235U(n,f) at incident energies of 1 to 20 MeV and for 235Cf(s.f.) were measured up to 4 MeV in coincidence with two parallel plate avalanche counters and the liquid scintillator array FIGARO. The unfolded γ-ray spectra from 1–4 MeV using the single value decomposition and iterative Bayesian techniques for the incident neutron energy regions corresponding to the first, second and third chance fissions were found to nearly identical and similar to the distribution from the spontaneous fission of 252Cf. General agreement with the γ-ray distributions from fission was also found with previous measurements.

Improvements have been made to the nuclear data standards largely as a result of an IAEA Data Development Project. The work includes the traditional activities related to standards, extending the energy ranges of some standards, and reference data that are not as well known as the standards but can be very useful in the measurements of certain types of cross sections. Also included is an effort to improve evaluations of 235U thermal and 252Cf spontaneous fission neutron spectra., JRC.D.4-Standards for Nuclear Safety, Security and Safeguards

Neutron radiography is one of the non-destructive testing techniques which can provide characterization complimentary to X-rays and in many cases unique information on the samples. The relatively h...

Many isotopes in nuclear materials exhibit strong peaks in neutron absorption cross sections in the epithermal energy range (1–1000 eV). These peaks (often referred to as resonances) occur at energies specific to particular isotopes, providing a means of isotope identification and concentration measurements. The high penetration of epithermal neutrons through most materials is very useful for studies where samples consist of heavy-Z elements opaque to X-rays and sometimes to thermal neutrons as well. The characterization of nuclear fuel elements in their cladding can benefit from the development of high resolution neutron resonance absorption imaging (NRAI), enabled by recently developed spatially-resolved neutron time-of-flight detectors. In this technique the neutron transmission of the sample is measured as a function of spatial location and of neutron energy. In the region of the spectra that borders the resonance energy for a particular isotope, the reduction in transmission can be used to acquire an image revealing the 2-dimensional distribution of that isotope within the sample. Provided that the energy of each transmitted neutron is measured by the neutron detector used and the irradiated sample possesses neutron absorption resonances, then isotope-specific location maps can be acquired simultaneously for several isotopes. This can be done even in the case where samples are opaque or have very similar transmission for thermal neutrons and X-rays or where only low concentrations of particular isotopes are present ( In this paper we present the proof-of-principle of NRAI and transmission Bragg edge imaging performed at Flight Path 5 (FP5) at the LANSCE pulsed, moderated neutron source of Los Alamos National Laboratory. A set of urania mockup fuel assemblies with intentionally introduced defects was investigated. The maps of elemental composition of pellets containing urania and tungsten were obtained simultaneously by resonance absorption imaging with spatial resolution better than ∼200 μm, while the voids and cracks were revealed by the transmission images obtained with thermal and cold neutrons. Our proof-of-principle experiments demonstrate that simultaneous acquisition of resonance and Bragg edge spectra enables concurrent mapping of isotope distributions, imaging of cracks and voids as well as measurements of some crystallographic parameters of fuel assemblies and their cladding. A detailed study of energy-dependent neutron statistics achievable at FP5 with our present detection system is also presented for a wide range of neutron energies.

The outgoing neutron energy spectra from neutron-induced fission of various actinides are important for basic understanding of the fission process near the scission point as well as playing a large role in neutron transport codes, which are heavily relied upon in the design of advanced nuclear reactors and simulations of critical assemblies. The reliability of the results of neutron transport models is a strong function of the quality of the nuclear data used as input. Currently, the world's experimental database of fission neutron spectra is severely incomplete (especially for higher incident neutron energies) with large uncertainties in key portions of the outgoing energy spectra. Many transport codes use evaluated data libraries, which are based on the approach of the Los Alamos model. Other theoretical models have been developed, but the available data cannot distinguish the results of different models (as is the case for 239Pu). Better measurements are needed for all incident and outgoing neutron energies, but most urgently in the low-energy (below 1 MeV) and high-energy (above 6 MeV) portions of the outgoing spectra where theoretical model results differ greatly. We present the design considerations (and some characterization results) of the two Chi-Nu neutron detector arrays: one array of 6Li-glass detectors and one array of liquid-scintillator detectors. These detector arrays are being constructed to meet the challenge of measuring the prompt fission neutron spectra (for a few common actinides) to a higher accuracy and precision than achieved previously and over a larger incident energy range than has been covered by previous experimenters. We see a significant reduction in neutron-scattering backgrounds with our new array designs.

Prompt-fission-neutron spectra for neutron-induced fission reactions on uranium and plutonium isotopes are important for nuclear applications. We have used 6 Li-glass scintillation detectors to measure outgoing neutron energies in the range from 10 keV to 1 MeV, where there is currently large uncertainty in nuclear data. To better understand the response of 6 Li-glass detectors in this energy range, measurements of well-known spontaneous-fission neutrons from a 252 Cf source were done in the neutron-beam flight path. Results were compared with Monte Carlo simulations and they show good agreement. Similar measurements with a 7 Li-glass detector were used to assess gamma-ray background yields.

Evaluations are being done for the H(n,n), 6Li(n,t), 10B(n,αγ), 10B(n,α), C(n,n), Au(n,γ), 235U(n,f) and 238U(n,f) standard cross sections. Evaluations are also being done for data that are not traditional standards including: the Au(n,γ) cross section at energies below where it is considered a standard; reference cross sections for prompt gamma-ray production in fast neutron-induced reactions; reference cross sections for very high energy fission cross sections; the 235U thermal neutron fission spectrum and the 252Cf spontaneous fission neutron spectrum and the thermal constants.

The neutron imaging diagnostic at the National Ignition Facility has been operating since 2011 generating neutron images of deuterium-tritium (DT) implosions at peak compression. The current design features a scintillating fiber array, which allows for high imaging resolution to discern small-scale structure within the implosion. In recent years, it has become clear that additional neutron imaging systems need to be constructed in order to provide 3D reconstructions of the DT source and these additional views need to be on a shorter line of sight. As a result, there has been increased effort to identify new image collection techniques that improve upon imaging resolution for these next generation neutron imaging systems, such as monolithic deuterated scintillators. This work details measurements performed at the Weapons Neutron Research Facility at Los Alamos National Laboratory that compares the radiographic abilities of the fiber scintillator with a monolithic scintillator, which may be featured in a future short line of sight neutron imaging systems.

Future high energy physics experiments at the energy and intensity frontiers will face challenges of a severe radiation environment from both ionization dose and charged and neutral hadrons. In this paper, we report an investigation on charged hadron-induced radiation damage in BGO, LYSO/LFS, PWO and a LYSO/W/Capillary shashlik cell by using 800 MeV and 24 GeV protons at LANL and CERN respectively. Degradations in both transmittance and light output are reported. The results show excellent radiation resistance of LYSO/LFS crystals and the LFS/W/Capillary shashlik cell against charged hadrons.

The distributions of prompt γ rays from the spontaneous fission of 252Cf and neutron-induced fission of 235U were measured up to ∼ 4 MeV using a liquid scintillator array. The unfolding of measured fission γ rays is presented using the Single Value Decomposition and iterative Bayesian methods. General agreement was found with comparisons made with previous measurements. The energy dependence of the prompt γ - ray distributions for the spontaneous fission of 252Cf and the neutron-induced fission of 235U from bombarding energies of 1-2, 5-10, and 10–20 MeV were found to be almost identical in the γ - ray energy region 1–4 MeV.

The SPectrometer for Ion DEtermination in fission Research (SPIDER) measures both position and time-of-flight (TOF) of charged particles using a system of thin carbon foils, electrostatic mirrors, microchannel plates, delay-line anodes, and a fast TDC. Tests have been conducted using 229Th and the alpha emitters in its decay chain. To date, timing resolution of 200 ps (FWHM) has been achieved corresponding to roughly 0.5% uncertainty in velocity measurements of fission fragments over a flight path of 52.1 cm. This velocity resolution, in combination with demonstrated fragment energy resolution is sufficient for 1 amu resolution of light mass fragments.

The ionization chamber component of the SPIDER detector has been designed to measure energy loss and kinetic energy of fragments produced through neutron-induced fission with energy resolutions of

Inertial Confinement Fusion (ICF) is undergoing more detailed research to increase neutron yield and will require high resolution imaging near the target. Neutron damage to diagnostics remains a serious issue in understanding and achieving ICF. We have demonstrated that Gallium Nitride (GaN) optoelectronic devices have exceptional neutron radiation hardness, by systematic testing of neutron radiation effects in GaN devices and materials with elevated neutron fluence levels and a broad neutron energy spectrum. During the 2013-2017 run cycles at Los Alamos Neutron Science Center (LANSCE), we irradiated various GaN materials and devices with fast and thermal plus resonance neutrons at several beamlines. This paper presents a radiation hardness study for Aluminum Gallium Nitride and Gallium Nitride (AlGaN/GaN) deep UV LEDs irradiated at the LANSCE 4FP60R beamline. The fluence level was up to 2.4 × 1013 neutrons/cm2 for neutrons with energies greater than 0.1 MeV. The device performance was monitored in real time. After three years of irradiation studies, we found that the GaN devices maintained operation in the forward active region. The current and voltage relation (I-V curves) varied insignificantly in the linear region. Our results demonstrate the radiation hardness needed for laser fusion diagnostics at least up to 1017 neutron yield per shot, if the diagnostics is placed 1 m away from the target, where the neutron fluence per shot is approximately 8 × 1011 n/cm2. The GaN devices can operate for multiple shots.

Cross-section measurements were made of prompt discrete γ -ray production as a function of incident neutron energy ( E n = 1 – 135 MeV ) on a 150Sm sample of 1550 mg / cm 2 of Sm 2 O 3 enriched to 95.6% in 150Sm. Results are compared with enhanced Hauser–Feshbach model calculations including the pre-equilibrium reactions. Energetic neutrons were delivered by the Los Alamos Neutron Science Center facility. The prompt-reaction γ -rays were detected with the compton-suppressed germanium array for neutron-induced excitations (GEANIE). Incident neutron energies were determined by the time-of-flight technique. Excitation functions for thirteen individual γ -rays up to E x = 0.8 MeV in 149Sm and one γ -ray transition between the first excited and ground state in 148Sm were measured. Partial γ -ray cross-sections were calculated using GNASH, an enhanced Hauser–Feshbach statistical nuclear reaction model code, and compared with the experimental results. The particle transmission coefficients were calculated with new systematic “global” optical model potential parameters. A coupled-channels optical model based on a soft rotor model was employed to calculate the particle transmission coefficients. The pre-equilibrium part of the spin-distribution in 150Sm was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK) and incorporated into the GNASH reaction model code. The partial cross-sections for discrete γ -ray cascade paths leading to the ground state in 149Sm and 148Sm have been summed (without double counting) to estimate lower limits for reaction cross-sections. These lower limits are combined with Hauser–Feshbach model calculations to deduce the reaction channel cross-sections. These reaction channel cross-sections agree with previously measured experimental and ENDF/B-VII evaluations.

Using a simple low-field NMR system, we monitored water content in a living tree in a greenhouse over two months. By continuously running the system, we observed changes in tree water content on a scale of half an hour. The data showed a diurnal change in water content consistent both with previous NMR and biological observations. Neutron imaging experiments show that our NMR signal is primarily due to water being rapidly transported through the plant, and not to other sources of hydrogen, such as water in cytoplasm, or water in cell walls. After accounting for the role of temperature in the observed NMR signal, we demonstrate a change in the diurnal signal behavior due to simulated drought conditions for the tree. These results illustrate the utility of our system to perform noninvasive measurements of tree water content outside of a temperature controlled environment.

Yttrium plays an important role as a radiochemical dosimetry detector for determining high energy 14 MeV neutron fluences, through measurement of (n,2n) activation products. The total (n,2n) cross section is known rather well from extensive activation measurements on the stable 89Y isotope, and from a previous activation measurement on the unstable 88Y ground state. However, until now the branching ratios to the ground state and excited isomers in 88Y via the 89Y (n,2n) reaction were not well known, and furthermore, uncertainty estimates were not available for these cross sections and branching ratios. This paper describes how gamma-ray transitions between states in (n,2n) and (n,n') reactions measured using the GEANIE detector at Los Alamos' LANSCE facility, together with theory predictions using the GNASH code, enable us to determine these quantities for the ENDF/B-VII evaluation. A previous measurement by Dietrich, at Livermore, provided important complementary information to the GEANIE analysis. We describe an uncertainty quantification analysis that uses the GNASH-KALMAN approach to evaluate cross sections for the 89Y (n,2n) population of the 88Y ground state and two meta-stable isomers (m1 and m2), along with their uncertainties. Our new results agree with Arthur's historic Los Alamos evaluated cross sections within a few percent below 15 MeV (with larger differences above 15 MeV). The (n,2n) cross sections to the 88Y ground state and m1, m2 isomers impact the average 88Y(n,2n)87Y cross section at leading-order; we determine this 14.1 MeV average cross section 88Y(n,2n)87Y = 1107 mb (± 4%), which agrees with the value obtained from Arthur's evaluation to 0.7%. An alternative method to predict cross sections, uncertainties, and covariance data, is described that uses the European TALYS reaction modeling code and a Backward-Forward Monte-Carlo uncertainty quantification technique. This approach uses a microscopic optical model, together with Hauser-Feshbach and preequilibrium reaction mechanisms, and the underlying model parameters and their uncertainties and correlations are determined through a Monte-Carlo filtering method based on comparisons with measured cross section data. We compare the results obtained using this approach with the GNASH-KALMAN method. The evaluated cross sections are rather similar in the two approaches. We show how the uncertainty information, as embodied in the resulting covariance matrices, is also qualitatively similar in both approaches.

Prompt γ-ray production cross sections were measured on a 48 Ti sample for incident neutron energies from I to 200 MeV. Partial γ-ray cross sections for transitions in 45-48 Ti, 45-48 Sc, and 43-45 Ca were determined. The observation of about 130 transitions from 11 different isotopes in the present work provides a demanding test of reaction model calculations, and is the first study in this mass region to extract partial γ-ray cross sections for many different reaction channels over a wide range of incident neutron energies. The neutrons were produced by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center/Weapons Neutron Research facility. The prompt-reaction y rays were detected with the large-scale Compton-suppressed GErmanium Array for Neutron Induced Excitations (GEANIE). Event neutron energies were determined by the time-of-flight technique. The γ-ray excitation functions were converted to partial γ-ray cross sections and then compared with model calculations using the enhanced GNASH reaction code. Compound nuclear, preequilibrium emission, and direct reaction mechanisms are included. Overall, the model calculations of the partial γ-ray cross sections are in good agreement with measured values.

Cross-section measurements were made of prompt gamma-ray production as a function of incident neutron energy (E{sub n} = 1 to 35 MeV) on an enriched (95.6%) {sup 150}Sm sample. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center (LANSCE) facility. The prompt-reaction gamma rays were detected with the large-scale Compton-suppressed Germanium Array for Neutron Induced Excitations (GEANIE). Neutron energies were determined by the time-of-flight technique. The {gamma}-ray excitation functions were converted to partial {gamma}-ray cross sections taking into account the dead-time correction, target thickness, detector efficiency and neutron flux (monitored with an in-line fission chamber). Partial {gamma}-ray cross sections were predicted using the Hauser-Feshbach statistical reaction code GNASH. Above E{sub n} {approx} 8 MeV the pre-equilibrium reaction process dominates the inelastic reaction. The spin distribution transferred in pre-equilibrium neutron-induced reactions was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK). These pre-equilibrium spin distributions were incorporated into a new version of GNASH and the {gamma}-ray production cross sections were calculated and compared with experimental data. The difference in the partial {gamma}-ray cross sections using spin distributions with and without pre-equilibrium effects is discussed.

In support of the Stewardship Science Academic Alliances initiative, an experimental program has been developed at Triangle Universities Nuclear Laboratory (TUNL) to measure (n,xn) cross-sections with both in-beam and activation techniques with the goal of improving the partial cross-section database for the NNSA Stockpile Stewardship Program. First experimental efforts include excitation function measurements on 235,238U and 241Am using pulsed and monoenergetic neutron beams with En = 5–15 MeV. Neutron-induced partial cross-sections were measured by detecting prompt γ rays from the residual nuclei using various combinations of clover and planar HPGe detectors in the TUNL shielded neutron source area. Complimentary activation measurements using DC neutron beams have also been performed in open geometry in our second target area. The neutron-induced activities were measured in the TUNL low-background counting area. In this presentation, we include detailed information about the irradiation procedures and facilities and preliminary data on first measurements using this capability.

The cross sections for populating the residual nucleus in the reaction AZX(n,x)A-4Z-2Y exhibit peaks as a function of incident neutron energy corresponding to the (n,n'α) reaction and, at higher energy, to the (n,2p3n) reaction. In addition, the relative magnitudes of these peaks vary with the Z of the target nucleus.

A multilayer thin-scintillator concept is described for ultrafast imaging. The individual layer thickness is determined by the spatial resolution and light attenuation length, the number of layers is determined by the overall efficiency. By coating the scintillators with a high quantum-efficiency photocathode, single X-ray photon detection can be achieved using fast scintillators with low light yield. The fast, efficient sensors, when combined with MCP and novel nanostructed electron amplification schemes, is a possible way towards GHz hard X-ray cameras for a few frames of images.

The multipolarity of a soft ( E γ = 3.3 ( 1 ) MeV ) resonance in the total radiative strength function (RSF) of 172 Yb is determined. For this reason, the level density and total RSF of 172 Yb have been extracted from primary- γ spectra from the 173 Yb( 3 He, αγ ) 172 Yb reaction. In a second experiment, two-step-cascade (TSC) intensities have been measured in the 171 Yb( n th , γ γ ) 172 Yb reaction. These intensities are compared to statistical-model calculations which are entirely based on experimental values of the level density and RSF from the former experiment. This comparison implies M1 assignment of the soft resonance. The strength of the M1 resonance is B ( M 1 ↑ ) = 6.5 ( 15 ) μ N 2 .

Two-step-cascade spectra of the 171Yb(n, γγ)172Yb reaction have been measured using thermal neutrons. They are compared to calculations based on experimental values of the level density and radiative strength function obtained from the 173Yb(3He, aγ)172Yb reaction. The multipolarity of a 6.5(15) μN2 resonance at 3.3(1) MeV in the strength function is determined to be M1 by this comparison.

A fission-fragment-sensitive detector built for low-energy photon spectroscopy applications at the WNR “white” neutron source at Los Alamos is described. The detector consists of eight layers of thin photovoltaic cells, onto which 1 mg / cm 2 of pure 238 U is deposited. The detector serves as an active target to select fission events from background and other reaction channels. The fairly small thickness of the detector with respect to transmission of 20– 50 keV photons permits the measurement of prompt fission-fragment X-rays. Results with the GEANIE photon spectrometer are presented.

Absolute partial γ-ray cross sections for discrete γ-ray production in the 239Pu(n,2nγi)238Pu reaction have been measured. The experiments were performed at LANSCE/WNR on the 60R neutron flight path. Reaction γ-rays were measured using the large-scale Compton-suppressed array of Ge detectors, GEANIE. The motivation for this experiment, an overview of the partial γ-ray cross-section measurement, and an introduction to the main experimental issues will be presented. The energy resolution of the Ge detectors allowed identification of reaction γ rays above the background of sample radioactivity and fission γ rays. The use of planar Ge detectors with their reduced sensitivity to neutron interactions and improved line shape was also important to the success of this experiment. Absolute partial γ-ray cross sections are presented for the 61+ → 41+ member of the ground state rotational band in 238Pu, together with miscellaneous other γ-ray partial cross sections. The n,2n reaction cross section shape and magnitude...

Future high energy physics experiments at the energy and intensity frontiers will face challenges from a severe radiation environment caused by both ionization dose and charged and neutral hadrons. This paper reports an investigation on proton induced radiation damage in various crystal scintillators. Large size BGO, LFS and PWO crystals of 18 to 22 cm long were irradiated by 800 MeV protons up to $3 \times 10^{15} p/cm^2$ at the WNR facility of LANSCE with longitudinal transmittance measured in situ. LYSO plates of $14 \times 14 \times 1.5 mm^3$ were irradiated by 24 GeV protons up to $8.2 \times 10^{15} p/cm^2$ at the IRRAD facility of CERN. Degradations in both transmittance and light output are reported. The results show an excellent radiation hardness of LYSO/LFS crystals against charged hadrons.

This paper examines the most popular advances in the FDTD algorithm development, as applied to electromagnetic wave propagation in linearly dispersive media. Several methodologies are presented, and comparisons are made in order to demonstrate the strengths and weaknesses of the various approaches. In particular, direct-integration and recursive-convolution schemes, associated with wave propagation in a cold plasma, Debye dielectrics, and Lorentz materials, are considered.

To meet the data acquisition requirements for five new neutron scattering instruments at the Los Alamos Neutron Science Center (LANSCE), we are building new systems using Web tools, commercial hardware and software, software developed by the controls community, and custom hardware developed by the neutron scattering community. To service these new instruments as well as seven existing instruments, our data acquisition system needs common software and hardware core capabilities and the means to flexibly integrate them while differentiating the needs of the diverse instrument suite. We report the features offered by our architecture that will simultaneously be functional and flexible, and then summarize the progress for hardware and software that can in fact meet the performance requirements demanded. We show how one of the five new instruments, the Spectrometer for Materials Research at Temperature and Stress, SMARTS, proposes to use the LANSCE data acquisition system for experiments that integrate event counting, real-time data analysis and slow controls.

Discrete {gamma}-ray spectra have been measured as a function of incident neutron energy for nuclei produced in the {sup 196}Pt(n,xn{gamma}) reactions. Spectroscopy was done using the large-scale Compton suppressed Ge {gamma}-ray spectrometer GEANIE. The {open_quotes}white{close_quotes} source neutron beam was produced at the Los Alamos Neutron Science WNR facility. Reaction neutron energy was determined using the time-of-flight technique. Reaction-channel yields were inferred from the measured intensity sum of the 2{sub 1}{sup +}{r_arrow}0{sub 1}{sup +} and the 2{sub 2}{sup +}{r_arrow}0{sub 1}{sup +} transitions for the {sup 196}Pt(n,xn) reactions for x{le}15. Weisskopf-Ewing calculations (including precompound) done with the HMS-ALICE code correctly predict the bulk of the (n,xn) reaction products for low multiplicity. However, they do not accurately predict yield ratios of the different (n,xn) reactions for x{ge}9. In addition, there is no consistent experimental indication of charged-particle reaction channels (n,pxn) for incident neutron energies above 60 MeV where they are predicted to account for approximately 1/3 of the total reaction cross section. Several possible causes are discussed for these discrepancies. Finally, the region of E-J phase space populated in this reaction is probed for several of the strongest reaction channels through the observation of relative yields for different yrast and off-yrast states. {copyright}more » {ital 1998} {ital The American Physical Society}« less

Prompt fission neutron spectra in the neutron-induced fission of ${}^{239}$Pu have been measured for incident neutron energies from 1 to 200 MeV at the Los Alamos Neutron Science Center. Mean energies deduced from the prompt fission neutron spectra (PFNS) lead to the observation of the opening of the second chance fission at 7 MeV and to indications for the openings of fission channels of third and fourth chances. Moreover, the general trend of the measured PFNS is well reproduced by the different models. The comparison between data and models presents, however, two discrepancies. First, the prompt neutron mean energy seems constant for neutron energy, at least up to 7 MeV, whereas in the theoretical calculations it is continuously increasing. Second, data disagree with models on the shape of the high energy part of the PFNS, where our data suggest a softer spectrum than the predictions.