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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Validation of neutron emission and neutron energy spectrum calculations on a Mega Ampere Spherical Tokamak with directional relativistic spectrum simulator

The recently developed directional relativistic spectrum simulator (DRESS) code has been validated for the first time against numerical calculations and experimental measurements performed on the Mega Ampere Spherical Tokamak . In this validation, the neutron emissivities and rates computed by DRESS are benchmarked against TRANSP/NUBEAM predictions while the neutron energy spectra provided by DRESS taking as input TRANSP/NUBEAM and ASCOT/BBNBI in Gyro-Orbit mode fast ion distributions are validated against proton pulse height spectra measured by the neutron flux monitor. Finally, excellent agreement was found between DRESS and TRANSP/NUBEAM predictions of local and total neutron emission.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Impact of Tensor Interaction on Beta-Delayed Neutron Emission from Neutron-Rich Nickel Isotopes

The Skyrme energy density functional including tensor interaction is used to describe microscopically multineutron delayed-neutron emission accompanying beta decay of even–even neutron-rich nickel isotopes of mass number in the range of A = 74−80. The respective calculations are performed in the quasiparticle random-phase approximation with allowance for the two-phonon components of the wave function for states of the daughter nucleus. The properties of the lowest quadrupole excitation of {sup 74,76,78,80}Ni are also studied. It is shown that a decrease in the strength of neutron–proton tensor interaction leads to a substantial hindrance of beta decay and to an increase in the probability for delayedneutron emission.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Prompt neutron emission in the neutron-induced fission of 239 Pu and the spontaneous fission of 252 Cf: an unfolding story

Prompt neutron emission is one of the major observables in fission and critical to a sustained chain reaction. The prompt neutron emission spectrum and its precision are essential for adequately modeling the chain reaction for any given application. Within this context, a joint program, called Chi-Nu, was initiated by LANL [1] with the objective to improve the precision of experimental measurements of prompt neutron emission for neutron-induced fission of 235 U and 239 Pu as well as the spontaneous fission of 252 Cf. The measurements were carried out at the Weapons Neutron Research Facility at Los Alamos Neutron Science Center using two scintillator arrays for neutron detection and a PPAC (parallel-plate avalanche counter) for fission-fragment detection.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Strong one-neutron emission from two-neutron unbound states in β decays of the r -process nuclei Ga 86 , 87

β-delayed one-neutron and two-neutron branching ratios (P$_{1n}$ and P$_{2n}$) have been measured in the decay of A = 84 to 87 Ga isotopes at the Radioactive-Isotope Beam Factory (RIBF) at the RIKEN Nishina Center using a high-efficiency array of 3 He neutron counters (BRIKEN). Two-neutron emission was observed in the decay of 84, 85, 87 Ga for the first time and the branching ratios were measured to be P$_{2n}$ = 1.6 (2)%, 1.3 (2)%, and 10.2 ( 28 ) stat ( 5 ) sys %, respectively. One-neutron branching ratio of 87 Ga (P$_{1n}$= 81 (9) stat (8) sys %) and half-life of 29(4) ms were measured for the first time. The branching ratios of 86 Ga were also measured to be P$_{1n}$ = 74 (2) stat (8) sys % and 16.2 (9) stat ( 6 ) sys % with better precision than a previous study. The observation that P$_{1n}$ > P$_{2n}$ for both 86,87 Ga was unexpected and is interpreted as a signature of dominating one-neutron emission from the two-neutron unbound excited states in 86, 87 Ge. In order to interpret the experimental results, shell-model and Hauser-Feshbach statistical model calculations of delayed particle and γ-ray emission probabilities were performed. This model framework reproduces the experimental results. The shell model alone predicts P$_{2n}$ significantly larger than P$_{1n}$ for the 87 Ga decay, and it is necessary to invoke a statistical description to successfully explain the observation that P$_{1n}$ > P$_{2n}$. Our new results demonstrate the relevance and importance of a statistical description of neutron emission for the prediction of the decay properties of multineutron emitters and that it must be included in the r -process modeling.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Detection of special nuclear material from delayed neutron emission induced by a dual-particle monoenergetic source

Detection of unique signatures of special nuclear materials is critical for their interdiction in a variety of nuclear security and nonproliferation scenarios. We report on the observation of delayed neutrons from fission of uranium induced in dual-particle active interrogation based on the {sup 11}B(d,n γ){sup 12}C nuclear reaction. Majority of the fissions are attributed to fast fission induced by the incident quasi-monoenergetic neutrons. A Li-doped glass–polymer composite scintillation neutron detector, which displays excellent neutron/γ discrimination at low energies, was used in the measurements, along with a recoil-based liquid scintillation detector. Time-dependent buildup and decay of delayed neutron emission from {sup 238}U were measured between the interrogating beam pulses and after the interrogating beam was turned off, respectively. Characteristic buildup and decay time profiles were compared to the common parametrization into six delayed neutron groups, finding a good agreement between the measurement and nuclear data. This method is promising for detecting fissile and fissionable materials in cargo scanning applications and can be readily integrated with transmission radiography using low-energy nuclear reaction sources.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Impact of Spontaneous Fission Neutron Emission Energy on Neutron Detector Response

A parametric study was simulated in MCNP to investigate the impact of spontaneous fission neutron energy on neutron detector response. A total of 880 configurations were simulated by varying 3 He pressure and polyethylene reflector thickness for 8 different isotopes. Results showed that deviations between the simulated isotopes become more prevalent at higher energies with 238 U showing the greatest deviation. It was also observed that configurations comparable to most detection setups, 10 atm and 6 - 8 cm polyethylene, were closer to the upper bound of deviations from a 252 Cf. 240 Pu, a common spontaneous fission source of interest, ranged from 2% - 3% within this space. This suggests that further investigation is required to determine exact correction factors when calibrating neutron detectors with a 252 Cf. Although demonstrated here for a 4π-detection system, future plans include simulating a more detailed model of the MC-15 detection setup to determine exact correction factors for future experiments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Development of a Reference Database for Beta-Delayed Neutron Emission

Beta-delayed neutron emission is important for nuclear structure and astrophysics as well as for reactor applications. Significant advances in nuclear experimental techniques in the past two decades have led to a wealth of new measurements that remain to be incorporated in the databases. In this work, we report on a coordinated effort to compile and evaluate all the available β-delayed neutron emission data. The different measurement techniques have been assessed and the data have been compared with semi-microscopic and microscopic-macroscopic models. The new microscopic database has been tested against aggregate total delayed neutron yields, time-dependent group parameters in 6-and 8-group re-presentation, and aggregate delayed neutron spectra. New recommendations of macroscopic delayed-neutron data for fissile materials of interest to applications are also presented. The new Reference Database for Beta-Delayed Neutron Emission Data is available online.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Fission-neutrons source with fast neutron-emission timing

A neutron source with fast timing has been built to help with detector-response measurements. The source is based on the neutron emission from the spontaneous fission of 252 Cf. The time is provided by registering the fission fragments in a layer of a thin scintillation film with a signal rise time of 1 ns. The scintillation light output is measured by two silicon photomultipliers with rise time of 0.5 ns. Overall time resolution of the source is 0.3 ns. Design of the source and test measurements using it are described. An example application of the source for determining the neutron/gamma pulse-shape discrimination by a stilbene crystal is also given.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Comparative study of neutron emission from a plasma focus device using two different anode shapes

The neutron emission from a low energy (2.2 kJ) plasma focus (PF) device operated with two different shapes (cylindrical and converging) of anodes has been investigated by employing photomultiplier tube and bubble dosimeter. The neutron emission with each anode is analyzed and the results are compared. It is found that the anode shapes strongly influenced the emission of neutron. The X-ray emission is found to be higher in case of converging anode, while neutron emission is found to be higher in case of cylindrical anode. The neutron yield and energy are found to be highly anisotropic in nature which indicates that the beam target mechanism plays a major role in the neutron emission in a PF device. The speed factor as well as the specific heat ratio of pinch column shows a good agreement with the experimentally observed results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Experimental validation of an integrated modelling approach to neutron emission studies at JET

An integrated modelling methodology for the calculation of realistic plasma neutron sources for the JET tokamak has been developed. The computational chain comprises TRANSP plasma transport and DRESS neutron spectrum calculations, and their coupling to the MCNP neutron transport code, bridging plasma physics and neutronics. Here, we apply the developed methodology to the analysis of neutron emission properties of deuterium and helium plasmas at JET, and validate individual modelling steps against neutron diagnostic measurements. Two types of JET discharges are modelled—baseline-like and three-ion radio-frequency scenarios—due to their diversity in plasma heating, characteristics of the induced fast ion population, and the imprint of these on neutron emission properties. The neutron emission modelling results are quantitatively compared to the total neutron yield from fission chambers, neutron emissivity profiles from the neutron camera, neutron spectra from the time-of-flight spectrometer, and neutron activation measurements. The agreement between measured and calculated quantities is found to be satisfactory for all four diagnostic systems within the estimated experimental and computational uncertainties. Additionally, the effect of neutrons not originating from the dominating D(D, n) 3 He reactions is studied through modelling of triton burnup DT neutrons, and, in mixed D- 3 He plasmas, neutrons produced in the 9 Be(D, nγ) 10 B reaction on impurities. It is found that these reactions can contribute up to several percent to the total neutron yield and dominate the neutron activation of samples. Finally, the effect of MeV-range fast ions on the neutron activation of 115 In and 27 Al samples is measured and computationally validated.

integrated modelling↗
DOE OSTI2020

Experiments with neutron induced neutron emission from U-235, Pu-239, and graphite

A neutron induced neutron emission experiment was conducted as the Los Alamos Neutron Science Center (LANSCE) facility at Los Alamos National Laboratory (LANL). In this experiment, a sample was placed in a well collimated neutron beam and was surrounded by an array of 28 fast neutron detectors (EJ-309). The experiment was performed with a neutron flight path of 21.5 m from the source to the sample, and 1 m from the sample to the detectors. The neutron emission from the sample was measured as a function of neutron time of flight covering an incident energy range from 0.7- 20 MeV. The samples included U-235, Pu-239, carbon (graphite), and blanks that matched the encapsulation of the sample. The measured samples were constantly cycled in and out of the neutron beam. This type of experiment measures neutron emission from all reactions occurring in the sample such as fission and elastic and inelastic scattering. Similar to the methodology previously developed at RPI, the measurements were compared with detailed simulations of the experiment using different cross section evaluations for the sample. The observed differences can be attributed to the evaluated neutron cross section and angular distributions. The carbon sample was used as a reference to validate both the experiment and simulation methodology and showed good agreement between experiments and simulations. A review of the experimental setup, analysis methods, and some of the results will be presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Detection of Fuel Pin Diversion via Fast Neutron Emission Tomography

Oak Ridge National Laboratory is developing a new capability to perform passive fast neutron emission tomography of spent nuclear fuel. The goal of this capability is to detect vacancies or substitutions of individual fuel pins in spent nuclear fuel assemblies for international safeguards applications, such as verifying the integrity of an assembly prior to transfer to “difficult to access” storage. Emission tomography uses collimation to isolate activity along “lines of response” through an object. By combining many collimated views through an object, the neutron emission from each fuel pin can be mathematically extracted and an image of the fuel assembly can be constructed. However, performing fast-neutron imaging is challenging for the very reason that it is desirable, namely, that fast neutrons penetrate a good deal of shielding and are consequently difficult to collimate and measure with high resolution. For spent fuel, additional challenges include the modest neutron source strength and the overwhelming gamma-ray emissions. While the International Atomic Energy Agency (IAEA) is presently investigating the use of passive gamma emission tomography for the same application, it is useful to investigate neutron emission tomography because fast neutrons better penetrate larger fuel assemblies and because fast neutrons (originating primarily from curium-244 which is mainly produced at the end of the exposure cycle) may be sensitive to replacement fuel pins that are subsequently irradiated. In the present work, we present a novel collimator concept that will enable rapid transaxial tomographic imaging of spent nuclear fuel using the spontaneous fast neutron emissions from the fuel. Initial design simulations of an imager based on this collimator indicate sufficient resolution to identify individual fuel pins. Employing such a collimator, the resulting imager can be sufficiently compact, efficient, and radiation resistant to make fast neutron emission imaging practical.

Iyengar, Anagha↗
DOE OSTI2016

Neutron-$\gamma$ competition for β-delayed neutron emission

Here we present a coupled quasiparticle random phase approximation and Hauser-Feshbach (QRPA+HF) model for calculating delayed particle emission. This approach uses microscopic nuclear structure information, which starts with Gamow-Teller strength distributions in the daughter nucleus and then follows the statistical decay until the initial available excitation energy is exhausted. Explicitly included at each particle emission stage is γ-ray competition. We explore this model in the context of neutron emission of neutron-rich nuclei and find that neutron-γ competition can lead to both increases and decreases in neutron emission probabilities, depending on the system considered. Finally, a second consequence of this formalism is a prediction of more neutrons on average being emitted after β decay for nuclei near the neutron drip line compared to models that do not consider the statistical decay.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS2009

Comparison of Image Restoration Methods for Lunar Epithermal Neutron Emission Mapping

Orbital measurements of neutrons by the Lunar Exploring Neutron Detector (LEND) onboard the Lunar Reconnaissance Orbiter are being used to quantify the spatial distribution of near surface hydrogen (H). Inferred H concentration maps have low signal-to-noise (SN) and image restoration (IR) techniques are being studied to enhance results. A single-blind. two-phase study is described in which four teams of researchers independently developed image restoration techniques optimized for LEND data. Synthetic lunar epithermal neutron emission maps were derived from LEND simulations. These data were used as ground truth to determine the relative quantitative performance of the IR methods vs. a default denoising (smoothing) technique. We review and used factors influencing orbital remote sensing of neutrons emitted from the lunar surface to develop a database of synthetic "true" maps for performance evaluation. A prior independent training phase was implemented for each technique to assure methods were optimized before the blind trial. Method performance was determined using several regional root-mean-square error metrics specific to epithermal signals of interest. Results indicate unbiased IR methods realize only small signal gains in most of the tested metrics. This suggests other physically based modeling assumptions are required to produce appreciable signal gains in similar low SN IR applications.

McClanahan, T. P.↗
DOE OSTI2025

The evidence of N = 16 shell closure and β -delayed neutron emission from 25 F

We measured the β -delayed neutron emission from 25 F for the first time at the Facility for Rare Isotope Beams (FRIB). Using combined neutron and γ -ray detector systems of the FRIB Decay Station Initiator (FDSi), we observed β -decay transitions populating neutron unbound states between 4.2 and 8 MeV in 25 Ne. The experimental results led to the revision of the β -decay half-life and β -delayed neutron-emission probability of 25 F. The β -decay strength distribution of 25 F extracted from the data agrees with the shell-model predictions using the USDB and SDPF-M effective interactions. This result indicates that the spherical neutron shell gap persists in 25 F and 25 Ne.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Quasi-differential neutron induced neutron emission reaction measurements at WNR

The quasi-differential neutron induced neutron emission reaction measurement (QD-NINE) method provides an additional benchmark which constrains cross-section evaluations and provides a measure of verification for existing evaluations. Experiments are preformed using an array of EJ-309 liquid scintillators at a variety of angles measuring the neutron scattering response from a sample.. An MCNP simulation is then compared to this experimental data and is run using various sets of evaluated nuclear data. Since the isotopes of interest for this measurement, {sup 235}U and {sup 239}Pu, are difficult to obtain, the WNR facility at LANL was chosen to perform the measurements utilizing the chi-nu detector array. A measurement of carbon has been performed and the high energy cutoff has been extended from 20 to 60 MeV compared with previous measurements using this method. An early stage simulation was compared to the experimental data and the results show good agreement. (authors)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2021

Thermonuclear neutron emission from a sheared-flow stabilized Z-pinch

We report the fusion Z-pinch experiment (FuZE) is a sheared-flow stabilized Z-pinch designed to study the effects of flow stabilization on deuterium plasmas with densities and temperatures high enough to drive nuclear fusion reactions. Results from FuZE show high pinch currents and neutron emission durations thousands of times longer than instability growth times. While these results are consistent with thermonuclear neutron emission, energetically resolved neutron measurements are a stronger constraint on the origin of the fusion production. This stems from the strong anisotropy in energy created in beam-target fusion, compared to the relatively isotropic emission in thermonuclear fusion. In dense Z-pinch plasmas, a potential and undesirable cause of beam-target fusion reactions is the presence of fast-growing, “sausage” instabilities. This work introduces a new method for characterizing beam instabilities by recording individual neutron interactions in plastic scintillator detectors positioned at two different angles around the device chamber. Histograms of the pulse-integral spectra from the two locations are compared using detailed Monte Carlo simulations. These models infer the deuteron beam energy based on differences in the measured neutron spectra at the two angles, thereby discriminating beam-target from thermonuclear production. An analysis of neutron emission profiles from FuZE precludes the presence of deuteron beams with energies greater than 4.65 keV with a statistical uncertainty of 4.15 keV and a systematic uncertainty of 0.53 keV. This analysis demonstrates that axial, beam-target fusion reactions are not the dominant source of neutron emission from FuZE. These data are promising for scaling FuZE up to fusion reactor conditions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

β-Delayed One and Two Neutron Emission Probabilities Southeast of 132 Sn and the Odd-Even Systematics in r-Process Nuclide Abundances

Here, the β-delayed one- and two-neutron emission probabilities (P 1n and P 2n ) of 20 neutron-rich nuclei with N≥82 have been measured at the RIBF facility of the RIKEN Nishina Center. P 1n of 130,131 Ag, 133,134 Cd, 135,136 In, and 138,139 Sn were determined for the first time, and stringent upper limits were placed on P2n for nearly all cases. β-delayed two-neutron emission (β2n) was unambiguously identified in 133 Cd and 135,136 In, and their P 2n were measured. Weak β2n was also detected from 137,138 Sn. Our results highlight the effect of the N=82 and Z=50 shell closures on β-delayed neutron emission probability and provide stringent benchmarks for newly developed macroscopic-microscopic and self-consistent global models with the inclusion of a statistical treatment of neutron and γ emission. The impact of our measurements on r-process nucleosynthesis was studied in a neutron star merger scenario. Our P 1n and P 2n have a direct impact on the odd-even staggering of the final abundance, improving the agreement between calculated and observed Solar System abundances. The odd isotope fraction of Ba in r-process-enhanced (r-II) stars is also better reproduced using our new data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗