Accession Number : AD0679141

Title :   MECHANISMS OF ENERGY TRANSFER IN DIELECTRICS.

Descriptive Note : Semiannual rept. no. 4, 1 Oct 67-30 Jun 68,

Corporate Author : NEW YORK UNIV N Y DEPT OF PHYSICS

Personal Author(s) : Brandt,Werner

Report Date : OCT 1968

Pagination or Media Count : 87

Abstract : A study of the processes determining moderation of electrons at energies below the internal ionization threshold of a dielectric is made. The probe used is the positron through its annihilation characteristics under a static electric field. These characteristics are related to the cross sections for electronic scattering and energy loss. Measurement on the positron annihilation spectrum of the insulators polyethylene and Teflon are given. As part of the work, we have improved the performance of subnanosecond delayed coincidence apparatus. In related work, data on the positron annihilation spectra of powders of small particle size is used to calculate positronium diffusion constants in the substances. Such powders can serve as high yield sources of free ortho-positronium and of gamma rays with continuous energy spectra. Investigation indicates a correlation between defect concentration and intensity of the longlived component of the positron annihilation spectra in alkali halides. The method of positron annihilation can provide an attractive complement to studies on color centers. (Author)

Descriptors :   (*DIELECTRICS, EXCITATION), (*POSITRONS, ANNIHILATION RADIATION), HALOCARBON PLASTICS, POLYETHYLENE PLASTICS, ALKALI METAL COMPOUNDS, HALIDES, COINCIDENCE COUNTING, POSITRONIUM, COLOR CENTERS, CRYSTAL DEFECTS, CORRELATION TECHNIQUES, GAMMA RAYS

Subject Categories : Solid State Physics

Distribution Statement : APPROVED FOR PUBLIC RELEASE