Danny R. Sprinkle

Free volume model for dielectric constant of polymer films

A slow positron flux generator reported in another paper at this conference was used to measure positron lifetime in a series of especially developed fluorine containing thin polyimide films. The positron lifetime spectra was analyzed into 2‐components using a standard least square routine. No evidence for positronium formation was observed in any of test films studied. The trapped positron lifetimes were used to calculate the radii of the shallow trap sites. Equating the total volume occupied by the traps with the saturation of the shallow trap sites. Equating the total volume occupied by the traps with the saturation moisture content of Kapton (reference) films, free volume fractions (f) were calculated in all the samples. These free volume fractions affect the dielectric constants (e) of the test films as follows: 1/e= (1−f)/eR+f(1−d)/eAir+fd/eWater Where, eR is the dielectric constant of the trap‐free medium, eAir is the dielectric constant of air, eWater is the dielectric constant of water, and d...

Gamma ray slush hydrogen monitor

Mass attenuation coefficients for 109Cd radiation have been measured in single phases and mixtures of phases of five chemical compounds. As expected, the mass attenuation coefficients are independent of the phases of the test chemicals. As a result of this study, it is recommended that a slush hydrogen monitoring system based on low energy gamma ray attenuation be developed for use on board the National Aerospace Plane.