Search NASA⌕ Search

SEARCH · Search NASA

Results for “Shells”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Space-dependent calculation of the multiplicity moments for shells

In earlier work, we extended the methodology of multiplicity counting in nuclear safeguards, by elaborating the one-speed stochastic transport theory of the calculation of the so-called multiplicity moments, i.e. the factorial moments of the number of neutrons emitted from a fissile item, following a source event from an internal neutron source (spontaneous fission and (α, n) reactions). Calculations were made for spheres and cylinders of various shapes. In all our work so far, the material of the items was homogeneous, and the distribution of the internal source was assumed to be uniformly distributed within the item, with the neutron emission assumed to be isotropic. In the present work the calculations are extended to the case of a point source inside either a solid sphere or in a spherical shell. This necessitates the extension of the theory to non-homogeneous items and non-uniform and non-isotropic sources. This work describes the extension of the theory and provides some quantitative results. (authors)

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Nucleon-Pair Shell Model within a Symmetry Broken Basis

The nucleon-pair shell model (NPSM) within the framework of a broken symmetry basis is studied. The results demonstrate the validity of such a scheme, which in turn leads to a significant reduction in the dimensionality of the multi-pair configuration space. Specifically, in the case of an axially-deformed basis, the results yield a satisfactory description of the low-lying spectrum, even without the need for applying the projection procedure. In the case of a triaxially-deformed basis, the result of variation after angular momentum projection suggest a potential for using the NPSM to find exact solutions in a semi-magic system.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1962

EFFECTS OF MODES OF INITIAL IMPERFECTIONS ON THE STABILITY OF CYLINDRICAL SHELLS UNDER AXIAL COMPRESSION

The effects of definite and "indefinite" initial imperfections on the buckling and post buckling behavior of an axially compressed cylindrical shell are analyzed by a nonlinear theory. The definite initial imperfections considered do not contribute to the reduction of the peak buckling load; while the "indefinite" imperfections, expressed in terms of a single factor introduced by Donnell 1 , cause a reduction in the buckling strength. The physical meaning of the imperfection factor, however, needs further clarification. Two theoretical buckling processes are found to be possible. In the early stage of buckling, the cylinder may deform with a comparatively large number of waves of small amplitudes or the cylinder may deform with a comparatively small number of waves of large amplitudes. Further theoretical and experimental studies of the effects of initial imperfections and the process of buckling are suggested.

AXIAL COMPRESSION↗