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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Simulation of Isotopic Concentrations and Gamma Spectra from Dynamic Fission Sources

A tool was developed to rapidly generate synthetic gamma-ray spectra to evaluate safeguards material control and accounting methods for liquid-fueled molten salt reactors. Molten salt reactor operations pose unique challenges to nuclear safeguards methods and protocols compared to deployed reactors designs (e.g., light water reactors). This research evaluates the use of gamma-ray spectroscopy to monitor fission product isotopic flow through a reactor model to understand expected operations and investigate changes to the spectra with material diversion scenarios. The large design space of molten salt reactors (e.g., liquid-fueled, liquid-cooled, online separations) could potentially lead to many measurement points within the reactor system. The developed analytical tool generates and evaluates synthetic gamma-ray spectra from dynamic reactor simulations by extracting isotopic inventory to generate source terms. An implementation in the Gamma Detector Response and Analysis Software (GADRAS) Application Program Interface (API) uses the source terms, a model of the reactor component, a detector response function, and measurement plan to quickly generate and analyze spectra. Prospective measurements are then evaluated in the more accurate but slower Geant4 simulations. Utilization of the developed modeling tool and analysis of the subsequent spectra enables optimization of collimation, shielding requirements, and expected count rates that are used to determine key measurement points in the modeled reactor design.

O'Brien, Sean↗
DOE OSTI2023

pyEGAF: An open-source Python library for the Evaluated Gamma-ray Activation File

The Evaluated Gamma-ray Activation File (EGAF) is one of the most comprehensive resources for thermal neutron-capture data. This database contains data from prompt gamma activation analysis measurements carried out in a consistent manner using the same experimental configuration at the Budapest Research Reactor for 245 isotopes. Although these valuable datasets have been freely available for many years, one of the drawbacks is the outdated and cryptic Evaluated Nuclear Structure Data File (ENSDF) format that is currently adopted for dissemination, making it difficult for users unfamiliar with the format to access and utilize the data contained therein. Furthermore, the ENSDF format does not readily lend itself to modern computational technologies and a parser is required to interpret the complicated mixed-record format. To help overcome these challenges, we have developed a translator to convert the ENSDF-formatted datasets into an open standard JavaScript Object Notation (JSON) format enabling accessibility to applications using different programming languages running in different environments. To compliment this effort, we have also developed an open-source software package implemented in Python, pyEGAF, that is designed to interact with the JSON data structures for general purpose access, manipulation, and analysis of the neutron-capture $\gamma$-ray data in EGAF. The new format, together with the pyEGAF library, greatly enhances access to the wider applications community where EGAF data may be useful or is required.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Scrutinizing the isotropic gamma-ray background in search of dark matter

The isotropic gamma-ray background (IGRB), measured by the Fermi Large Area Telescope, is the result of several classes of extragalactic astrophysical sources. Those sources include blazars, start-forming galaxies and radio galaxies. Also, ultrahigh-energy cosmic rays interacting with the infrared background contribute to the isotropic background. Using information from Fermi’s gamma-ray sources catalog and the results of dedicated studies of these classes of sources, from observations at the infrared and radio, we model their contribution to the IGRB. In addition to conventional astrophysical sources, dark matter may be a component of the IGRB. We combine our model of conventional astrophysical sources and of dark matter annihilation in distant galaxies, marginalizing over relevant uncertainties, to derive constraints on the dark matter annihilation cross section, from the measured IGRB. In calculating the contribution from dark matter we include the flux from extragalactic halos and their substructure and also the subdominant contribution from the Milky Way’s halo at high galactic latitudes. The resulting constraints are competitive with the strongest current constraints from the dwarf spheroidal galaxies. Under certain dark matter assumptions, we also find an indication for a small excess flux in the isotropic background. Here, our results are consistent with the gamma-ray excess at GeV energies toward the galactic center.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Gamma-based nuclear fusion measurements at inertial confinement fusion facilities

Experiments performed on an inertial confinement fusion (ICF) platform offer a unique opportunity to study nuclear reactions, including reaction branches that are useful for diagnostic applications in ICF experiments as well as several that are relevant to nuclear astrophysics. In contrast to beam-accelerator experiments, experiments performed on an ICF platform occur over a short time scale and produce a plasma environment with physical parameters that are directly relevant to big bang and/or stellar nucleosynthesis. Several reactions of interest, such as D(T,γ) 5 He, H(D,γ) 3 He, H(T,γ) 4 He, and T( 3 He,γ) 6 Li produce high-energy gamma rays. S factors or branching ratios for these four reactions have recently been studied using various temporally-resolved Cherenkov detectors at the Omega laser facility. This work describes these detectors as well as the current standard technique for performing these measurements. Recent results for reactions D(T,γ) 5 He, H(D,γ) 3 He, H(T,γ) 4 He, and T( 3 He,γ) 6 Li are reviewed and compared to accelerator-based measurements. Limitations associated with implosion experiments and use of the current standard gamma detectors are discussed. A basic design for a gamma spectrometer for use at ICF facilities is briefly outlined.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

GRB 221009A: The B.O.A.T. Burst that Shines in Gamma Rays

We present a complete analysis of Fermi Large Area Telescope (LAT) data of GRB 221009A, the brightest gamma-ray burst (GRB) ever detected. The burst emission above 30 MeV detected by the LAT preceded, by 1 s, the low-energy (<10 MeV) pulse that triggered the Fermi Gamma-Ray Burst Monitor (GBM), as has been observed in other GRBs. The prompt phase of GRB 221009A lasted a few hundred seconds. It was so bright that we identify a bad time interval of 64 s caused by the extremely high flux of hard X-rays and soft gamma rays, during which the event reconstruction efficiency was poor and the dead time fraction quite high. The late-time emission decayed as a power law, but the extrapolation of the late-time emission during the first 450 s suggests that the afterglow started during the prompt emission. We also found that high-energy events observed by the LAT are incompatible with synchrotron origin, and, during the prompt emission, are more likely related to an extra component identified as synchrotron self-Compton (SSC). A remarkable 400 GeV photon, detected by the LAT 33 ks after the GBM trigger and directionally consistent with the location of GRB 221009A, is hard to explain as a product of SSC or TeV electromagnetic cascades, and the process responsible for its origin is uncertain. Because of its proximity and energetic nature, GRB 221009A is an extremely rare event.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Inline gamma-spectrometry of fission product elements after rapid high-pressure ion chromatographic separation

Analysis of irradiated material shortly after irradiation can be non-trivial due to highly radioactive activation and fission isotopes increasing dead time in gamma-ray detection systems, often requiring a “cooling-period” between receipt of a sample and the subsequent analysis. A direct separation–detection method has been developed combining ion chromatography and inductively coupled mass spectrometry for rapid, low-level analysis of fission products; it cannot, however, detect certain short-lived species below the detection limit of the system. In this paper we report the implementation of an inline gamma-ray detector, which was added post-separation, pre-analysis, to test the quality and utility of elementally-isolated gamma-ray spectroscopy.

Inline gamma-ray detection↗
DOE OSTI2023

Use of Compton suppression gamma ray spectrometry to determine 239 Pu

We report 239 Pu has been characterized by gamma-ray spectroscopy for a level higher than the usual environmental ones typically needing alpha spectrometry, ICP-MS or TIMS. The higher activities typically have applications in reprocessing, safeguards verification, and nuclear forensics. For activities of hundreds of Bq/g, it is possible to use gamma ray spectrometry for 239 Pu characterization. A soil reference standard of 185 Bq/g (75 ng/g) was measured on a 79% efficient HPGe with a digital Compton suppression system. The ratios of the counting statistics for suppressed and unsuppressed uncertainties for various 239 Pu photopeaks were determined. The effects of self-attenuation on the low energy gamma rays were evaluated, and it was determined that Compton suppression was an effective characterization method of 239 Pu after accounting for self-attenuation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2026

Measurement of gamma-induced reactions between 10 and 19 MeV on natural zinc with potential application to 67 Cu production

As part of a broader campaign to understand gamma-induced charged particle emission with multiple materials, the cross sections of the (γ, p), and (γ, α) reactions on a natural zinc target were measured. Here, these cross sections were measured experimentally using a kinematically-complete, event-by-event methodology, using monoenergetic gamma ray beams from the High Intensity Gamma Source (HIγS) facility, ranging from 10 to 19 MeV, to bombard a natural metallic zinc target in vacuum. The measured cross sections are compared with theoretical predictions using the statistical model approach, which is important for the use of such models in real-world applications such as the production of the 67 Cu theranostic via the 68 Zn(γ, p) reaction.

Gamma-induced reactions↗
DOE OSTI2023

Evaluation of Preoperative and Intraoperative Mobile Gamma Camera Imaging in Sentinel Lymph Node Biopsy for Melanoma Independent of Preoperative Lymphoscintigraphy

Sentinel lymph node biopsy (SLNB) is standard practice for staging cutaneous melanoma. High false negative rates have increased interest in adjunctive techniques for localizing SLNs. Mobile gamma cameras (MGCs) represent potential tools to enhance SLNB performance. Twenty eligible melanoma patients underwent 99mTc sulfur colloid injection and standard lymphoscintigraphy with a fixed gamma camera (FGC). A survey using a 20 cm square MGC, performed immediately preoperatively by the study surgeon, was used to establish an operative plan while blinded to the FGC results. Subsequently, SLNB was performed using a gamma probe and a novel 6 cm diameter handheld MGC. A total of 24 SLN basins were detected by FGC. Prior to unblinding, all 24 basins were identified with the preoperative MGC, and the operative plan established by preoperative MGC imaging was confirmed accurate by review of the FGC images. All individual SLNs were identified during intraoperative MGC imaging, and in 5/24 (21%) cases, additional clinical information was obtained from the MGC. Preoperative MGC images provide information consistent with FGC images for planning SLNB and in some cases provides additional information that aided in surgical decision-making.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

Accelerated radiation transport modeling techniques for pencil beam computed tomography using gamma rays

Monte Carlo radiation transport modeling studies were performed for a compact, and high-resolution gamma-ray computed tomography system designed for imaging irradiated nuclear fuel. The system comprises a 60 Co source – chosen for its highly penetrating 1173 keV and 1332 keV gamma rays – a pair of high-aspect-ratio pencil beam collimators, and an inorganic scintillator detector. Here two acceleration methods are proposed to rapidly model a transmission type gamma-ray tomography system. The first, a variance reduction technique, is based on performing Monte Carlo simulations with a monodirectionally-biased source, sampled from a characteristic sub-volume of the full source volume. The second acceleration method is based on the deterministic calculations using the Beer–Lambert law and detector response characteristics. Comparison of simulations using acceleration approaches with analog simulations of the fully isotropic, full-volume equivalent, show that the Monte Carlo variance reduction technique gives quantitatively accurate predictions for large collimator aspect ratios while the deterministic calculations are semi-quantitative but converge close to the correct result as the collimator aspect ratio increases. As such, these techniques can be used to reduce the computational cost in generating simulated radiographs and tomographs by several orders of magnitude. Experimental validation efforts are currently underway and will be demonstrated in future work.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Optimizing the spatial resolution and gamma discrimination of SiPM-based Anger cameras

SiPM Anger cameras have been designed for use as 2-dimensional thermal neutron detectors for scientific applications such as at single crystal diffraction instruments. These cameras utilize a neutron sensitive scintillator and an array of SiPM photosensors, separated by a light spreading glass. While this optics package is very effective at detecting and positioning neutrons, it is also sensitive to gamma rays, which are a source of unwanted noise. In this work, we underwent a search of scintillator and spreader glass thicknesses to determine the optimal combination for maximizing spatial resolution. Both experimental results and GEANT4 simulations are presented. Further, to address the issue of gamma ray detection, we have also designed and presented a multi-layer scintillator that reduces the amount of scintillation light produced via gamma-ray energy deposition, allowing for easier pulse-height discrimination. A sample of this geometry has been produced that results in a factor of 2 improvement over an equivalent thickness monolithic scintillator.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Integrating HPC simulations and physical experiments to characterize the effects of gamma radiation on seismic protective devices

Seismic protective systems, composed of seismic isolators and dampers, can substantially reduce the effects of earthquake shaking on nuclear power plants and components therein. To enable the use of these devices to protect equipment inside a plant and close to a source of radiation, the U.S. Department of Energy (DOE) funded a project at the Idaho National Laboratory (INL) and the University at Buffalo to characterize the effects of absorbed gamma dose on their mechanical properties. An early task in the project was to determine the exposure time required in the INL Foss Therapy Services (FTS) 60 Co gamma irradiator to achieve a target absorbed dose in the materials used to construct isolators and dampers, including fluids, polymers, composites, and metals. This task required the novel integration of high-performance computing (HPC), Monte Carlo N-Particle (MCNP) simulations, and irradiation experiments using Fricke dosimetry. An MCNP model of the FTS irradiator at INL was developed and validated using Fricke dosimetry. Simulations of three experiments in the irradiator, two with Fricke vials only and one with Fricke vials and a large-size isolator, predicted the Fricke-measured absorbed dose rate to within 15% in all three cases, providing high confidence in the calculation of the gamma dose absorbed in the materials comprising the seismic protective devices. The simulations demonstrated that the effects of photon scattering on absorbed dose rate in the FTS irradiator are negligible for test articles installed close to the cobalt sources and near the rear of the irradiator. The validated MCNP model of the FTS irradiator is being used to support ongoing DOE-funded experiments on seismic protective devices and could be applied to future, non-seismic-related experiments. In conclusion, the novel validation process successfully deployed for the FTS irradiator at INL could be applied to other irradiators, requiring new MCNP models and simulations, and irradiation experiments using dosimeters.

42 - ENGINEERING↗
DOE OSTI2024

Comparison of effects from gamma, e-beam and X-ray radiation on multilayer polymer films used in biopharmaceutical devices by chemometric treatment of spectroscopic data

The present study investigated the effects of gamma-ray, electron beam, and X-ray radiation on polymers in EVA/EVOH/EVA multilayer films. Spectroscopic methods, including FTIR and UV–Vis, were employed in conjunction with chemometric treatments such as PCA, SIMPLISMA treatments, and PLS models. The feasibility of dose prediction on multilayer film, given a known dose, is attainable across various irradiation technologies. Both gamma ray and X-ray exhibit comparable effects on the multilayer film, and it is feasible to anticipate the dose released on the film by utilizing UV–Vis spectra or infrared spectra for gamma ray or X-ray of a predetermined dose.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2024

Multiscale Modeling of Plutonium Radiation Chemistry in Nitric Acid Solutions. 1. Cobalt-60 Gamma Irradiation of Pu(IV)

We report careful manipulation of the plutonium oxidation states is essential in the study and utilization of its rich redox chemistry. To achieve this level of control, a comprehensive mechanistic understanding of radiation-induced plutonium redox chemistry is critical due to the unavoidable exposure of plutonium to ionizing radiation fields, both inherent and from in-process applications. To this end, we have developed an experimentally evaluated multiscale computer model for the prediction of gamma radiation-induced Pu(IV) redox chemistry in concentrated nitric acid solutions (1.0, 3.0, and 6.0 M). Under these acidic, aqueous solution conditions, cobalt-60 gamma irradiation afforded marginal net conversion of Pu(IV) to Pu(VI), the extent of which was dependent on the concentration of HNO 3 and absorbed gamma dose. Multiscale calculations, which are in excellent agreement with experimental data, indicate that this observation is due to a combination of inherent plutonium disproportionation reactions and several radiation-induced processes, including redox cycling between Pu(IV) and Pu(III), as achieved by the reduction of Pu(IV) by nitrous acid and hydrogen peroxide, the oxidation of Pu(III) by nitrate and hydroxyl radicals, and the sequential oxidation of Pu(IV) to Pu(V) and Pu(VI) by the remaining available yield of nitrate radicals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Evidence for a high-energy tail in the gamma-ray spectra of globular clusters

Millisecond pulsars are very likely the main source of gamma-ray emission from globular clusters. However, the relative contributions of two separate emission processes – curvature radiation from millisecond pulsar magnetospheres versus inverse Compton emission from relativistic pairs launched into the globular cluster environment by millisecond pulsars – have long been unclear. To address this, we search for evidence of inverse Compton emission in 8-yr Fermi–LAT data from the directions of 157 Milky Way globular clusters. We find a mildly statistically significant (3.8σ) correlation between the measured globular cluster gamma-ray luminosities and their photon field energy densities. However, this may also be explained by a hidden correlation between the photon field densities and the stellar encounter rates of globular clusters. Analysed in toto, we demonstrate that the gamma-ray emission of globular clusters can be resolved spectrally into two components: (i) an exponentially cut-off power law and (ii) a pure power law. The latter component – which we uncover at a significance of 8.2σ – has a power index of 2.79 ± 0.25. It is most naturally interpreted as inverse Compton emission by cosmic-ray electrons and positrons injected by millisecond pulsars. Here, we find the luminosity of this power-law component is comparable to, or slightly smaller than, the luminosity of the curved component, suggesting the fraction of millisecond pulsar spin-down luminosity into relativistic leptons is similar to the fraction of the spin-down luminosity into prompt magnetospheric radiation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

The TRAPUM L -band survey for pulsars in Fermi -LAT gamma-ray sources

ABSTRACT More than 100 millisecond pulsars (MSPs) have been discovered in radio observations of gamma-ray sources detected by the Fermi Large Area Telescope (LAT), but hundreds of pulsar-like sources remain unidentified. Here, we present the first results from the targeted survey of Fermi-LAT sources being performed by the Transients and Pulsars with MeerKAT (TRAPUM) Large Survey Project. We observed 79 sources identified as possible gamma-ray pulsar candidates by a Random Forest classification of unassociated sources from the 4FGL catalogue. Each source was observed for 10 min on two separate epochs using MeerKAT’s L-band receiver (856–1712 MHz), with typical pulsed flux density sensitivities of $\sim 100\, \mu$Jy. Nine new MSPs were discovered, eight of which are in binary systems, including two eclipsing redbacks and one system, PSR J1526−2744, that appears to have a white dwarf companion in an unusually compact 5 h orbit. We obtained phase-connected timing solutions for two of these MSPs, enabling the detection of gamma-ray pulsations in the Fermi-LAT data. A follow-up search for continuous gravitational waves from PSR J1526−2744 in Advanced LIGO data using the resulting Fermi-LAT timing ephemeris yielded no detection, but sets an upper limit on the neutron star ellipticity of 2.45 × 10−8. We also detected X-ray emission from the redback PSR J1803−6707 in data from the first eROSITA all-sky survey, likely due to emission from an intrabinary shock.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

On the gamma-ray emission from the core of the Sagittarius dwarf galaxy

ABSTRACT We use Fermi-LAT data to analyse the faint gamma-ray source located at the centre of the Sagittarius (Sgr) dwarf spheroidal galaxy. In the 4FGL-DR3 catalogue, this source is associated with the globular cluster, M54. We investigate the spectral energy distribution and spatial extension of this source, with the goal of testing two hypotheses: (1) the emission is due to millisecond pulsars within M54, or (2) the emission is due to annihilating dark matter from the Sgr halo. For the pulsar interpretation, we consider a two-component model which describes both the lower-energy magnetospheric emission and possible high-energy emission arising from inverse Compton scattering. We find that this source has a point-like morphology at low energies, consistent with magnetospheric emission, and find no evidence for a higher-energy component. For the dark matter interpretation, we find the signal favours a dark matter mass of mχ = 29.6 ± 5.8 GeV and an annihilation cross section of $\sigma v = (2.1 \pm 0.59) \times 10^{-26} \, \text{cm}^3$ s−1 for the $b \bar{b}$ channel (or mχ = 8.3 ± 3.8 GeV and $\sigma v = (0.90 \pm 0.25) \times 10^{-26} \, \text{cm}^3$ s−1 for the τ+τ− channel), when adopting a J-factor of $J=10^{19.6} \, \text{GeV}^2 \, \text{cm}^{-5}$. This parameter space is consistent with gamma-ray constraints from other dwarf galaxies and with dark matter interpretations of the Galactic Centre Gamma-Ray Excess.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Axion constraints from quiescent soft gamma-ray emission from magnetars

We report axion-like-particles (ALPs) emitted from the core of a magnetar can convert to photons in its magnetosphere. The resulting photon flux is sensitive to the product of (i) the ALP-nucleon coupling G an which controls the production cross section in the core and (ii) the ALP-photon coupling g aγγ which controls the conversion in the magnetosphere. We study such emissions in the soft-gamma-ray range (300 keV to 1 MeV), where the ALP spectrum peaks and astrophysical backgrounds from resonant Compton up scattering are expected to be suppressed. Using published quiescent soft-gamma-ray flux upper limits in five magnetars obtained with CGRO COMPTEL and INTEGRAL SPI/IBIS/ISGRI, we put limits on the product of the ALP-nucleon and ALP-photon couplings. We also provide a detailed study of the dependence of our results on the magnetar core temperature. We further show projections of our result for future Fermi-GBM observations. Our results motivate a program of studying quiescent soft-gamma-ray emission from magnetars with the Fermi-GBM.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗