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SynopsisIsotactic polypropylene (Profax) film samples irradiated in the Pennsylvania State University (PSU) reactor at ambient temperatures were examined by solvent extraction and infrared absorption techniques. At low irradiation doses, samples annealed (density = 0.909 g./cc. a t 24°C.) prior to irradiation were found to have a lower gel content and a higher concentration of oxidation products than quenched samples (density = 0.899 g./cc. a t 24OC.) irradiated under identical conditions. Similar gel fraction results were obtained for electron irradiated samples of polypropylene. These effects are believed to arise from the accumulation of a greater concentration of free macroradicals in the higher density samples. At higher reactor dosages the irradiation effects in the annealed and quenched films appear to be about the same. The gel content as a function of dose was found to be independent of the irradition intensity level over a twofold range. Irradiations in the PSU reactor were also carried out on high density polyethylene (Marlex 50) pellets a t two temperatures, viz., 40 f 10°C. and 150°C. Irradiation at 150°C. led to a greater gel content a t any given dose, a result in agreement with that reported by Lawton, Balwit, and Powell for electron-irradiated specimens. Nuclear magnetic resonance spectra were obtained for molded annealed samples of partially isotactic polypropylene, irradiated in the Brookhaven reactor, at temperatures of 90-330°K. The observed shifts in the line narrowing process that occur in the 270-330°K. region are explained in terms of the decrease in crystallinity and the increasing density of crosslinks that accompany irradiation.

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Depth-dose distributions of 10-MeV electrons incident on homogeneous media of carbon, aluminum, polyethylene, and polystyrene have been measured using thin radiochromic dye-film dosimeters. Two types of dye-film dosimeters were employed as "cavities" within the media in two different geometrical configurations. One configuration was a stack with the dosimeters interleaved between disks of the medium and placed perpendicular to the incident electron beam direction. The other configuration was a wedge assembly with a single piece of dye film placed between pieces of the medium at a small angle to the beam direction. • The results show no significant difference between dosimeter type or experimental arrangement. In addition, good agreement is shown in comparisons of experimental and Monte Carlo calculated depth-dose distributions characterized by such parameters as extrapolated range, depth of peak dose, and ratio of peak to entrance dose.