A Multiple Radiation Effects Facility for the Study of Structural and Flexible Materials Exposed to the Space Environment
A radiation effects facility is described which utilizes multiple radiation sources, vacuum chambers and thermal control to simulate the space environment. Use of the facility for eight months' continuous testing of thin film flexible materials is discussed and summary results, primarily from in-situ testing, are presented.
Development of a ground-based facility for simulating the omnidirectional near-earth electron environment
Abstract A method is detailed for simulating in the laboratory the omnidirectional near-earth electron environment. This technique can synthesize the directional and energy properties of an arbitrary omnidirectional electron flux by combining a sufficient number of weighted energy and direction increments. A large vacuum chamber has been built, capable of holding three-dimensional structures up to 30 cm in each dimension while maintaining pressures in the 10−6 mm Hg range. The support structure in the chamber rotates around two axes, thereby achieving all angular orientations necessary for the omnidirectional simulation. This chamber was coupled with a beam scanning system to a 4 MeV electron Van de Graaff accelerator which was tuned to provide specified fluences of electrons at the desired energies. The system was used to irradiate a series of hollow aluminum cubes having varying wall thicknesses. Using radiochromic film dosimeters, dose profiles were mapped in the interiors for both one-wall and six-wall exposures. Results of the dose mapping are presented for several monoenergetic cases as well as for the energy spectra from a 235U fission event. The one-wall exposures show dose variations within the interior by a factor of 3.2 ± 0.6 independent of energy or wall thickness. In the six-wall exposure, distributions varied only about 15%.
The infection process, sporulation and survival of Alternaria helianthi on sunflower
SUMMARY 
 
Electron microscopy was used to study the infection of sunflower leaves by Alternaria helianthi. Conidia germinated by producing one to many germ tubes which grew across the leaf surface before forming appressoria. The fungus directly penetrated its host through the cuticle and epidermis. Entry into the host through wounds and stomates was also observed. Extracellular sheaths were found to be associated with germ tubes and intercellular hyphae of A. helianthi. Conidiophores developed through collapsed stomates, from leaf veins, trichomes and also from mycelium growing across the host leaf surface. Microcylic conidia were produced directly from parent conidia under certain conditions. Studies using a volumetric spore trap showed that the airborne spore concentration followed a distinct periodicity with peaks occurring between 0900 and 1100 h each day. Laboratory studies showed that safflower, noogoora burr and bathurst burr could serve as alternative hosts for A. helianthi. The pathogen was readily isolated from sunflower crop debris from a diseased crop that had been harvested 1 yr earlier.