Accession Number:

AD0415685

Title:

INELASTIC SCATTERING OF NEUTRONS BY ANHARMONIC CRYSTALS,

Descriptive Note:

Corporate Author:

CORNELL UNIV ITHACA NY

Report Date:

1963-01-01

Pagination or Media Count:

31.0

Abstract:

The purpose of this study was to determine the phonon frequencies and lifetimes from these experiments. When a crystal has anharmonicities interference effects can occur between processes in which the neutron creates several phonons these coherences are due to the fact that when a phonon can decay into several phonons, the final state in which the neutron has created one phonon is not orthogonal to final states in which the neutron has created several phonons. It is shown that the Placzek sum rule is still a valid guide in subtracting the multiphonon background from the experimental cross-section. The remaining cross-section is the sum of the one-phonon cross-section and the one-phonon, several-phonon interference terms. The one phonon cross-section has a resonance at the phonon frequency, with a width proportional to the inverse of the phonon lifetimm0-however, the interference terms have the effect of shift ing the center of this resonance, as observed, from the one-phonon frequency, and also changing the shape from an expected Lorentizian form. Author

Subject Categories:

Distribution Statement:

APPROVED FOR PUBLIC RELEASE