Accession Number : AD0688179

Title :   MECHANISMS OF ENERGY TRANSFER IN DIELECTRICS.

Descriptive Note : Semi-annual rept. no. 5, 31 Dec 68-31 Jul 69,

Corporate Author : NEW YORK UNIV N Y RADIATION AND SOLID STATE LAB

Personal Author(s) : Brandt,Werner

Report Date : APR 1969

Pagination or Media Count : 32

Abstract : The processes pertinent to the relaxation of electrons at energies below internal ionization energy of a dielectric are studied. The probe used is the positron through its annihilation characteristics. A model is presented which relates the amount of positronium formed in a substance containing small concentrations of impurities with a lower ionization potential than the pure substance to the scattering and energy loss cross sections for positrons and electrons at energies below the lowest electronic excitation level of the pure substance. The positron annihilation spectra in polyethylenes and polytetrafluorethylenes of differing crystallinities subject to applied electric fields have been measured as part of our program of obtaining data from which the cross sections determining the transient electronic response of a dielectric to ionizing radiation can be determined. Positron annihilation is also being developed as a probe for investigating the changes in defect concentration in alkali halides which are produced by X-ray irradiation. (Author)

Descriptors :   (*DIELECTRICS, EXCITATION), (*POSITRONS, ANNIHILATION RADIATION), NONDESTRUCTIVE TESTING, POLYETHYLENE PLASTICS, ALKALI METAL COMPOUNDS, HALIDES, COINCIDENCE COUNTING, CRYSTAL DEFECTS, POSITRONIUM, COLOR CENTERS, CORRELATION TECHNIQUES, ELECTRIC FIELDS, X RAYS

Subject Categories : Solid State Physics

Distribution Statement : APPROVED FOR PUBLIC RELEASE