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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Intense gamma-ray source based on focused electron beams from a laser wakefield accelerator

Laser wakefield accelerators generate ultrashort electron bunches with the capability to produce γ-rays. Here, we produce focused laser wakefield acceleration electron beams using three quadrupole magnets. Electron beams are then focused into a 3 mm lead converter to generate intense, focused bremsstrahlung γ beams. Experimental results demonstrate the generation and propagation of focused γ beams to a best focus spot size of 2.3 ± 0.1 × 2.7 ± 0.2 mm 2 using a copper stack calorimeter. Monte Carlo simulations conducted using GEANT4 are in good agreement with experimental results and enable detailed examination of γ-ray generation. Simulations indicate that the focused γ beams contained 2.6 × 10 9 photons in the range of 100 keV to 33 MeV with an average energy of 6.4 MeV. A γ-ray intensity of 7 × 10 10 W/cm 2 was estimated from simulations. In conclusion, the generation of focused bremsstrahlung γ-ray sources can have important applications in medical imaging applications and laboratory astrophysics experiments.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Gamma-ray measurements for inertial confinement fusion applications

High-energy γ rays generated from inertial confinement fusion (ICF) experiments have become an important signature for studying the dynamics of implosion processes. Due to their high-energy and penetrating nature, γ rays are the most unperturbed fusion products, which can preserve the original birth information of the fusion process. Fusion γ rays provide a direct measure of nuclear reaction rates (unlike x rays) without being compromised by Doppler spreading (unlike neutrons). However, unambiguous γ-ray measurements for ICF study further required a decade-long period of technological development, which included a deepening understanding of fusion γ-ray characteristics and innovations in instrument performance. This review article introduces the production mechanism of the prompt and secondary γ rays and various ICF performance parameters (e.g., bang time and burn width), which can be derived from γ-ray measurement. A technical overview will be followed by summarizing γ-ray detectors fielded or proposed, especially for high-yield ICF experiments at the Omega Laser Facility and National Ignition Facility. Over the past few years, γ-ray diagnostic technologies have been extended beyond ICF research. A few examples of non-ICF applications of γ-ray detectors are introduced at the end of this article.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Unsupervised Learning for Improved Gamma-Ray Spectrometry in Pixelated Cadmium Zinc Telluride (CZT) Detectors

Machine learning has been found to be ubiquitously useful across many industries, presenting an opportunity to improve radiation detection performance using data-driven algorithms. Improved detector resolution can aid in the detection, identification, and quantification of radionuclides. Here, in this work, a novel, data-driven, unsupervised learning approach is developed to improve detector spectral characteristics by learning, and subsequently rejecting, poorly performing regions of the pixelated detector. Feature engineering is used to fit individual characteristic photo peaks to a Doniach lineshape with a linear background model. Then, principal component analysis is used to learn a lower-dimension latent space representation of each photo peak where the pixels are clustered, and subsequently ranked, based on the cluster mean distance to an optimal point. Pixels within the worst cluster(s) are rejected to improve the full-width at half-maximum (FWHM) by 10% to 15% (relative to the bulk detector) at 50% net efficiency when applied to training data obtained from measurements of a 100 μCi 154 Eu source using a H3D M400i pixelated cadmium zinc telluride detector. These results compare well with, but do not outperform, a greedy algorithm that accumulates pixels in order of FWHM from lowest to highest used as a benchmark. In the future, this approach can be extended to include the detector energy and angular response. Finally, the model is applied to newly seen natural and enriched uranium spectra relevant for nuclear safeguards applications.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Sensitivity of the Cherenkov Telescope Array for probing cosmology and fundamental physics with gamma-ray propagation

The Cherenkov Telescope Array (CTA), the new-generation ground-based observatory for γ astronomy, provides unique capabilities to address significant open questions in astrophysics, cosmology, and fundamental physics. We study some of the salient areas of γ cosmology that can be explored as part of the Key Science Projects of CTA, through simulated observations of active galactic nuclei (AGN) and of their relativistic jets. Observations of AGN with CTA will enable a measurement of γ absorption on the extragalactic background light with a statistical uncertainty below 15% up to a redshift z=2 and to constrain or detect γ halos up to intergalactic-magnetic-field strengths of at least 0.3 pG . Extragalactic observations with CTA also show promising potential to probe physics beyond the Standard Model. The best limits on Lorentz invariance violation from γ astronomy will be improved by a factor of at least two to three. CTA will also probe the parameter space in which axion-like particles could constitute a significant fraction, if not all, of dark matter. We conclude on the synergies between CTA and other upcoming facilities that will foster the growth of γ cosmology.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Spectroscopy of a sample of unidentified gamma-ray Fermi sources

ABSTRACT The fourth-DR3 version (4FGL-DR3) of the Fermi-LAT catalogue of γ-ray sources contains ∼1000 objects at a galactic latitude |b| > 10° that are not identified with an optical counterpart. We performed a systematic study of these sources, focusing on 190 objects that have a unique X-ray counterpart in the available Swift/XRT observations. Optical counterparts were then selected, and optical spectra were found in the literature for 33 sources. We found that 21 could be classified as BL Lac objects. Among these, we were able to provide the redshift for eight of them, while for two others we established a lower limit to the redshift by detecting intervening absorption. The other 12 objects display optical spectra with prominent emission lines (0.036 < z < 1.65). These spectra are characterized by both broad and narrow emission lines, with the exception of three sources. One of these displays only broad emission lines, while the other two exclusively exhibit narrow lines. On the basis of the radio/optical flux ratio, all BL Lac objects in this study are radio-loud. Four sources out of the 12 with prominent emission lines can be classified as radio-loud, while at least five of the 12 sources with prominent lines are radio-quiet. This is somewhat unexpected, given the radio-loudness distribution of 4FGL-associated blazars.

Ulgiati, Alberto (ORCID:0009000736025276)↗
DOE OSTI2026

Gamma rays and gravitational waves from inelastic Higgs portal dark matter

We explore a simple and predictive dark matter scenario involving a complex scalar field, ϕ , coupled to the Higgs portal with no additional field content. In the UV, the field possesses a global U ( 1 ) symmetry which is broken by mass terms and Higgs portal interactions. In the mass basis, the complex field splits into a pair of real scalars with a small mass splitting (in analogy to pseudo-Dirac fermions), such that the Higgs portal acquires both diagonal and off-diagonal terms with respect to these eigenstates. In the parameter space where the off-diagonal interaction predominates, this scenario is safe from direct detection constraints. Moreover, this model provides a viable explanation for the longstanding Galactic Center γ -ray excess. Additionally, this model influences the Higgs potential in a way that could facilitate a strong first-order electroweak phase transition in the early Universe, potentially leading to a stochastic gravitational wave background that could fall within the reach of upcoming space-based detectors.

Hooper, Dan [Wisconsin U., Madison] (ORCID:0009000↗
DOE OSTI2025

Constraints on dark matter with future MeV gamma-ray telescopes

A number of new balloon or space-based γ -ray observatories have been proposed to close a “MeV gap” in sensitivity to γ rays in the MeV–GeV energy band. One aspect of the science case for these instruments is their ability to constrain or discover decaying or annihilating dark matter. In this work, we forecast the sensitivity of these instruments for dark matter annihilation or decay for a range of possible Standard Model final states and compare to existing bounds. Published by the American Physical Society 2025

O’Donnell, Kayla E. (ORCID:0009000532266844)↗
DOE OSTI2025

First observations of solar halo gamma rays over a full solar cycle

We analyze 15 years of Fermi-LAT data and produce a detailed model of the Sun’s inverse-Compton scattering emission (solar halo), which is powered by interactions between ambient cosmic-ray electrons and positrons with sunlight. By developing a novel analysis method to analyze moving sources, we robustly detect the solar halo at energies between 31.6 MeV and 100 GeV, and angular extensions up to 45° from the Sun, providing new insight into spatial regions where there are no direct measurements of the Galactic cosmic-ray flux. The large statistical significance of our signal allows us to subdivide the data and provide the first 𝛾-ray probes into the time variation and azimuthal asymmetry of the solar modulation potential, finding time-dependent changes in solar modulation both parallel and perpendicular to the ecliptic plane. Our results are consistent with (but with independent uncertainties from) local cosmic-ray measurements, unlocking new probes into astrophysical processes near the solar surface.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Dynamic Testing of a Commercial FRAM Device Under Gamma Ray Dose and Neutron Beam

Here, this work presents dose rate and neutron testing on a ferroelectric random-access memory (FRAM) device in dynamic operation during radiation pulses. Radiation failure modes are shown to be unique. Dose rate failure is shown to be based primarily on integrated dose in the radiation pulse and terminates the FRAM operation and can alter up to 8 bytes of data in storage. Neutron failures are attributed to a shifting of data like a clocking error.

Harris, Nathan↗
DOE OSTI2025

Improved field assessments of chemicals and explosives using high-resolution gamma-ray spectroscopy with a tagged neutron interrogation system

A field-portable tagged neutron interrogation system is being developed for detection of explosives and chemical warfare agents by prompt γ-ray neutron activation analysis. The system combines an associated particle imaging deuterium-tritium neutron generator with a high-purity germanium γ-ray detector. Fine spatial resolution neutron and α detectors enable precise mapping of characteristic γ-ray emission distributions onto high-clarity neutron radiographic images. A narrow coincidence gate associated with each tagged neutron ensures a large signal-to-background ratio, thus significantly improving sensitivity to the chemical compositions of the items being assessed. Recent experimental results recorded from test objects involving mock explosives and other chemicals are presented.

Bucher, Brian [Idaho National Laboratory (INL)]↗