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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Analysis of temperature-dependent neutron transmission and self-indication measurements on tantalum at 2-keV neutron energy

The method of pseudo-resonance cross sections is used to analyze published temperature-dependent neutron transmission and self-indication measurements on tantalum in the unresolved region. In the energy region analyzed, 1825.0 to 2017.0 eV, a direct application of the pseudo-resonance approach using a customary average strength function will not provide effective cross sections which fit the measured cross section behavior. Rather a local value of the strength function is required, and a set of resonances which model the measured behavior of the effective cross sections is derived. This derived set of resonance parameters adequately represents the observed resonance hehavior in this local energy region. Similar analyses for the measurements in other unresolved energy regions are necessary to obtain local resonance parameters for improved reactor calculations. This study suggests that Doppler coefficients calculated by sampling from grand average statistical distributions over the entire unresolved resonance region can be in error, since significant local variations in the statistical distributions are not taken into consideration.

Semler, T. T.↗
NASA NTRS1991

The shear modulus of the neutron star crust and nonradial oscillations of neutron stars

Shear moduli are calculated for bcc crystalline and rapidly quenched Coulomb solids produced by the Monte Carlo simulation method. The shear moduli are calculated up to the transition temperature and include the effects of thermal fluctuations. An effective shear modulus appropriate to an approximate 'isotropic' body is introduced. It is found that the values of the 'average shear modulus' for the quenched solids remain about the same as those for the corresponding bcc crystals, although the individual shear moduli of the former, disordered solids deviate considerably from the cubic symmetry of the latter. These results are applied to analyses of neutron star oscillations. It is found that the periods of the two interfacial modes are increased by about 10 percent compared to previous results, and that s-mode periods are increased by about 30 percent. The periods of the f and p modes are hardly affected at all. The surface g-mode periods are not greatly affected, while the t-mode periods are increased by 20-25 percent.

Strohmayer, T.↗
NASA NTRS2011

Lunar Reconnaissance Orbiter (LRO) Observations with the Lunar Exploration Neutron Detector (LEND): Neutron Suppression Regions (NSR) and Polar Hydrogen

Orbital detection of neutrons has become the dominant remote sensing technique for detecting and inferring H concentrations and its spatial distribution beneath planetary surfaces [Lawrence et al, (2010) Icarus, 205, pp. 195-209, Mitrofanov et al (2007) Science 297(5578), 78-81]. Indications for the presence of localized and relatively high water content was provided by LRO and LCROSS. LEND identified Cabeus, as the most promising LCROSS impact site [Mitrofanov I. et al. (2010) Science, 330, 483], and instruments onboard LRO and LCROSS have measured signatures of water, H2 and other volatiles in the impact plume [Colaprete A. et al. (2010) Science, 339,463, Gladstone R. et al. (2010) Science, 330, 472].

Chin, G.↗
DOE OSTI2024

Measurement of D-T Neutron Source Flux by SelfNeutron Activation Analysis with a LaBr3 Detector

Conclusions: • Decay of 78Br produced from the 79Br(n,2n) reaction in LaBr3 is present in the spectrum plotted in the time domain. • The neutron production rate reconstructed from preliminary LaBr3 estimate is smaller than the generator output. • Generator characterization may become more routine if a simple and robust method is made available for applications. Ongoing work: • Implementing bootstrapping to improve error estimates. • Examining threshold and edge effects of LaBr3

SMITH, MURRY↗
DOE OSTI2024

Actinides and Neutron Scattering at the Spallation Neutron Source and High Flux Isotope Reactor

The importance of actinides for science, technology, and medicine is widely recognized and does not require a lengthy introduction. However, the fundamental understanding of actinides and their chemical and physical properties lags behind the knowledge of most other elements in the periodic table. Most actinides (89 ≤ Z ≤ 103) are man-made and were produced in particle accelerators or nuclear reactors in the second half of the 20th century. Although trends in bonding and electronic structure are well characterized and documented across the periodic table, fundamental questions remain regarding the chemistry and physics of the actinides. This lack of knowledge is largely because most isotopes of actinides are intensely radioactive, which greatly increases the difficultly in handling them.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗