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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Sensitivity of the Cherenkov Telescope Array to spectral signatures of hadronic PeVatrons with application to Galactic Supernova Remnants

The local Cosmic Ray (CR) energy spectrum exhibits a spectral softening at energies around 3 PeV. Sources which are capable of accelerating hadrons to such energies are called hadronic PeVatrons. However, hadronic PeVatrons have not yet been firmly identified within the Galaxy. Several source classes, including Galactic Supernova Remnants (SNRs), have been proposed as PeVatron candidates. The potential to search for hadronic PeVatrons with the Cherenkov Telescope Array (CTA) is assessed. The focus is on the usage of very high energy γ-ray spectral signatures for the identification of PeVatrons. Assuming that SNRs can accelerate CRs up to knee energies, the number of Galactic SNRs which can be identified as PeVatrons with CTA is estimated within a model for the evolution of SNRs. Additionally, the potential of a follow-up observation strategy under moonlight conditions for PeVatron searches is investigated. Statistical methods for the identification of PeVatrons are introduced, and realistic Monte-Carlo simulations of the response of the CTA observatory to the emission spectra from hadronic PeVatrons are performed. Based on simulations of a simplified model for the evolution for SNRs, the detection of a γ-ray signal from in average 9 Galactic PeVatron SNRs is expected to result from the scan of the Galactic plane with CTA after 10 h of exposure. Finally, CTA is also shown to have excellent potential to confirm these sources as PeVatrons in deep observations with $\mathscr{O}$ (100) hours of exposure per source.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

New insights into backbending in the symmetry-adapted shell-model framework

Here we provide insights into the backbending phenomenon within the symmetry-adapted framework which naturally describes the intrinsic deformation of atomic nuclei. For 20 Ne, the canonical example of backbending in light nuclei, the ab initio symmetry-adapted no-core shell model shows that while the energy spectrum replicates the backbending from experimental energies under the rotor-model assumption, there is no change in the intrinsic deformation or intrinsic spin of the yrast band around the backbend. For the traditional example of 48 Cr, computed in the valence shell with empirical interactions, we confirm a high-spin nucleus that is effectively near-spherical, in agreement with previous models. However, we find that this spherical distribution results, on average, from an almost equal mixing of deformed prolate shapes with deformed oblate shapes. Microscopic calculations confirm the importance of spin alignment and configuration mixing, but surprisingly unveil no anomalous increase in moment of inertia. Furthermore, this finding opens the path toward further understanding the rotational behavior and moment of inertia of medium-mass nuclei.

20 ≤ A ≤ 38↗
NASA NTRS1971

Electron transport and space shielding handbook

The transport of electrons through material is discussed with emphasis on space radiation problems. Brief reviews of the electron radiation environment and electron transport properties are presented. Parametric representations of the electron transmitted fraction, energy spectrum, angular distribution, backscatter coefficient, and energy deposition are given as functions of electron energy and target material. Parametric equations for thick target bremsstrahlung are presented. Calculations of the transport of isotropically incident electrons relevant to space applications are shown. Comparisons of parametric representation with data, photon attenuation coefficients, electron energy deposition data, flux-to-dose conversion relations, and formalism applicable to space shielding problems are presented.

Shreve, D. C.↗
NASA NTRS1972

Discovery of the binary nature of SMC X-1 from Uhuru.

The X-ray source in the Small Magellanic Cloud SMC X-1 was observed by Uhuru on numerous occasions from December 1970 through April 1972. As previously reported by Leong et al. (1971), the source was seen to be variable. It was found that SMC X-1 occults with a period of 3.8927 days. The energy spectrum is cut off at low energies and flat. There is no large-amplitude periodic pulsation. The luminosity observed makes the binary source SMC X-1 comparable in strength to both the stronger galactic sources and the discrete sources in the Large Magellanic Cloud.

Schreier, E.↗
NASA NTRS1973

Lunar orbital gamma ray measurements from Apollo 15 and Apollo 16.

Examination of the data obtained by gamma-ray spectrometers on the Apollo 15 and Apollo 16 spacecraft has been carried out in part by summing up broad regions of the energy spectrum. The most instructive of these energy regions is 0.55 to 2.75 MeV, where the difference in count rates observed can be accounted for mainly by variations in the Th, U, and K content of the surface layers. The highest values are found in Mare Imbrium and Oceanus Procellarum, where a good deal of local variation is observed. By contrast, little increase is seen in the eastern maria surveyed compared with count rates in highland areas. The broad highland regions are low in radioactivity, but there is a measurable rise near the southernmost latitude on the far side. In addition to the radioactive lines, gamma-ray lines which can be ascribed to O, Si, Fe, Mg, and Al have been identified.

Arnold, J. R.↗
NASA NTRS1979

Galaxies and gamma-ray astronomy

The nature of the high-energy spectra of several types of active galaxies and their contribution to the measured diffuse gamma-ray emission between 1 and 150 MeV are considered, using X-ray spectra of active galaxies and SAS 2 data regarding the intensity upper limits to the gamma-ray emission above 35 MeV. It is found that a substantial increase in slope of the photon energy spectrum must occur in the low energy gamma-ray region for Seyfert galaxies, BL Lac objects, and emission line galaxies; the power-law spectra observed in the X-ray range must steepen substantially between 50 keV and 50 MeV. In addition, a cosmological integration shows that Seyfert galaxies, BL Lac objects, and quasars may account for most of the 1-150 MeV diffuse background, even without significant evolution.

Bignami, G. F.↗
NASA NTRS1983

Implications of high-energy neutron observations from solar flares

The time-dependent flux of high-energy neutrons discovered from the solar flare of 1980 June 21 provides a new technique for determining the total number and energy spectrum of accelerated protons and nuclei at the sun. The implications of these observations on gamma-ray emission, relativistic electron spectrum and number, proton and electron energy contents, and the location of the interaction region are also examined.

Ramaty, R.↗
NASA NTRS1986

Energetics analysis of the observed and simulated general circulation using three-dimensional normal mode expansions

The energetics characteristics of the observed and simulated general circulation are analyzed using three-dimensional normal mode expansions. The data sets involved are the Goddard Laboratory for Atmospheres (GLA) analysis and simulation data and the Geophysical Fluid Dynamics Laboratory (GFDL) analysis data. The spectral energy properties of the Rossby and gravity modes and energy transformations are presented. Significant influences of model characteristics and the assimilation techniques are observed in the barotropic energy spectrum, particularly for the gravity mode. Energy transformations of the zonal mean field in the GLA analysis and simulation are similar, but distinctly different from that in the GFDL analysis. However, overall, the energy generation in the baroclinic mode is largely balanced by the sink in the barotropic mode. The present study may demonstrate utilities of the three-dimensional normal mode energetics in the analysis of the general circulation.

Tanaka, Hiroshi↗
NASA NTRS1986

A possible SAR arc energization source - Precipitating electrons

Coincident measurements by ground-based photometers and satellite-borne electron sensors have shown the association of precipitating electrons and Stable Auroral Red Arcs at midlatitudes. Modeling of these events has suggested that, within the constraints imposed by uncertainties of the electron energy spectrum, the electron influx carries sufficient energy to establish ionospheric temperatures required to power the arcs.

Slater, D. W.↗
NASA NTRS1992

Constraints on electron acceleration in the Crab nebula

Using the radio through hard X-ray images of the Crab nebula to derive the spatial dependence of the electron spectrum and the magnetic field distribution from MHD flow models, we have rederived the high-energy spectrum of inverse Compton scattered gamma rays. We find agreement with the observed spectrum at TeV energies, but it is clear that the inverse Compton flux does not contribute significantly to the unpulsed nebular emission observed by COS-B from 50 to 500 MeV, which is consistent with a smooth continuation of the spectrum in hard X-rays. The emission at these energies must therefore be due to synchrotron radiation by electrons of at least PeV energies. It appears that the emission in the high-energy gamma-ray range, sensitive to the highest energy electrons in the nebula, can put interesting constraints on the acceleration mechanism.

Harding, A. K.↗
NASA NTRS1974

Lunar neutron capture as a tracer for regolith dynamics

The Apollo 17 Lunar Neutron Probe Experiment measured both the boron-10 neutron capture rate and the uranium-235 neutron-induced fission rate as a function of depth. Cd absorption gave a measure of the neutron energy spectrum. Comparisons of the results are made with theory, and good agreement is obtained for the magnitudes and depth dependences of the capture rates. While the low-energy neutron spectrum at depth agrees with theory, the spectrum near the peak of the flux profile is harder than predicted. In light of these results, several alternatives for interpreting the magnitude and uniformity of the neutron capture data from lunar surface soil samples are outlined. While none of the alternatives can be unquestionably defended or discarded, a surface layer mixing model is discussed in detail.

Burnett, D. S.↗
NASA NTRS2012

Computational Transport Modeling of High-Energy Neutrons Found in the Space Environment

The high charge and high energy (HZE) particle radiation environment in space interacts with spacecraft materials and the human body to create a population of neutrons encompassing a broad kinetic energy spectrum. As an HZE ion penetrates matter, there is an increasing chance of fragmentation as penetration depth increases. When an ion fragments, secondary neutrons are released with velocities up to that of the primary ion, giving some neutrons very long penetration ranges. These secondary neutrons have a high relative biological effectiveness, are difficult to effectively shield, and can cause more biological damage than the primary ions in some scenarios. Ground-based irradiation experiments that simulate the space radiation environment must account for this spectrum of neutrons. Using the Particle and Heavy Ion Transport Code System (PHITS), it is possible to simulate a neutron environment that is characteristic of that found in spaceflight. Considering neutron dosimetry, the focus lies on the broad spectrum of recoil protons that are produced in biological targets. In a biological target, dose at a certain penetration depth is primarily dependent upon recoil proton tracks. The PHITS code can be used to simulate a broad-energy neutron spectrum traversing biological targets, and it account for the recoil particle population. This project focuses on modeling a neutron beamline irradiation scenario for determining dose at increasing depth in water targets. Energy-deposition events and particle fluence can be simulated by establishing cross-sectional scoring routines at different depths in a target. This type of model is useful for correlating theoretical data with actual beamline radiobiology experiments. Other work exposed human fibroblast cells to a high-energy neutron source to study micronuclei induction in cells at increasing depth behind water shielding. Those findings provide supporting data describing dose vs. depth across a water-equivalent medium. This poster presents PHITS data suggesting an increase in dose, up to roughly 10 cm depth, followed by a continual decrease as neutrons come to a stop in the target.

Cox, Brad↗