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Proceedings Paper

Energy-dependent total thermal-neutron-scattering cross-section and transport of a neutron pulse in Fullerite at 300 K
Author(s): Shri-Prakash Tewari; Poonam Silotia; Kakoli Bera; Aditya Saxena
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Paper Abstract

Crystalline fullerine-fullerite- is a molecular crystal and therefore possesses a number of dynamical modes: librational, orientational-diffusive, tunnelling and optical in addition to the usual anisotropic translational modes. Making use of these dynamical modes a thermal neutron scattering kernel for fullerite has been developed. The total neutron scattering cross-section of thermal neutrons have been computed in the energy range 10-4 - 0.3 eV. For inelastic scattering while one phonon and two phonon processes are sufficient, for libron exchanges as many as thirteen libron quanta exchanges have to be considered. Using the thermal neutron scattering kernel the multigroup Boltzmann transport equation has been diagonalized, to obtain its eigenvalue and corresponding eigenfunctions of a neutron pulse propagating in the medium. The variation of lowest eigenvalue with the size of the assembly is compared with the corresponding measured values in graphite and it turns out to be slower in smaller assemblies of fullerite. The time dependent thermalization of the neutron pulse, introduced in the assembly at time t=0, has also been computed. While for large assembly (B2=0.0006 /cm-2) the high energy neutron pulse gets thermalised in about 1500 μs, it takes as long as 5000 μs for smaller assemblies ( B2=0.005 /cm-2).

Paper Details

Date Published: 27 October 2003
PDF: 12 pages
Proc. SPIE 5219, Nanotubes and Nanowires, (27 October 2003); doi: 10.1117/12.505772
Show Author Affiliations
Shri-Prakash Tewari, Univ. of Delhi (India)
Poonam Silotia, Univ. of Delhi (India)
Kakoli Bera, Univ. of Delhi (India)
Aditya Saxena, Univ. of Delhi (India)

Published in SPIE Proceedings Vol. 5219:
Nanotubes and Nanowires
Akhlesh Lakhtakia; Sergey Maksimenko, Editor(s)

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