Bruce J. Faraday

The Fiber Optic Dosimeter on the Navigational Technology Satellite 2

A fiber-optic radiation dosimeter has been developed that utilizes the darkening induced in silicate glasses by ionizing radiation. A small, light weight, low-power consuming dosimeter package was deployed on the Navigational Technology Satellite 2. Observed real-time accumulated absorbed dose behind three shield thicknesses for the period July 1977 - June 1978 are compared with both the AE4 and the AEI7 particle fluence models for outer zone trapped electrons. The observations indicate little shielding improvement above three g/cm2 due to the presence of bremsstrahlung generated within the shielding and give evidence of a harder energy spectrum than predicted by these models. Occasional large dose rate fluctuations may correlate with sunspot activity during late 1977 and early 1978.

Thermal annealing of proton-irradiated silicon solar cells

Solar cells made from 1.5- and 10-Ωċcm p-type silicon, with silver-titanium evaporated electrodes, were irradiated by 4.6-MeV protons at room temperature to fluences ranging from 1 × 1010to 1 × 1012protons/cm2. The photovoltaic current-voltage characteristics, the photovoltaic spectral response, and the minority carrier diffusion length were studied as the solar cells were annealed isochronally to temperatures up to 600°C. The proton radiation damage annealed in two stages, the first occurring between 50° and 150°C, and the second between 350° and 450°C. The removal of proton damage in this manner differs markedly from the annealing reported for 1-MeV electron damage, where practically no recovery of the photovoltaic properties is observed below 350°C. At any selected annealing temperature, the 10-Ω ċ cm cells were observed to recover to a slightly greater degree than the 1.5-Ω ċ cm type.

Defect Clusters in Electron-Irradiated Silicon

Calculations of the formation of disordered regions in silicon due to irradiation by high energy (15-45 MeV) electrons indicate that a sufficient concentration of defect clusters is produced to affect the electrical properties of the material. Isochronal annealing of room temperature radiation-induced degradation in the short-circuit current of silicon solar cells and in the minority carrier lifetime of the p-type base region is studied up to 500°C. The existence of a low temperature (50-200°C) annealing stage is shown to be independent of dopant and oxygen impurity concentration. It is inferred that this stage, which is similar to those observed in fast neutron- and in proton-irradiated silicon, is characteristic of cluster formation.

Annealing of proton radiation damage in silicon solar cells

Abstract A thermal annealing study of silicon solar cells irradiated by 4.6 MeV protons at 30°C revealed that the radiation-induced degradation in the photovoltaic was annealed in two stages. The first stage occurs in the range from 50° to 200°C while the second is observed between 325° and 450°C.

Testing of materials for solar power space applications

Abstract This paper summarizes the results of a program initiated at the Naval Research Laboratory to test conventional and state-of-the-art solar power space systems by flying them aboard satellites. The program (approximately nine years in duration) confirmed the practicality of improvements in advanced silicon solar cells such as textured surfaces, shallow junctions, back surface field and back surface reflector techniques, as well as novel methods of bonding coverslips to conventional cells. In addition, the performance of gallium aluminum arsenide solar cells first tested in a space environment and demonstrated to be satisfactory. Finally, advanced silicon cells such as lithium-diffused and vertical junction cells, which were reported to be radiation resistant on the basis of measurements in the laboratory, were found unsuitable for extended space application.

New Materials Technology For Improving The Efficiency Of Photovoltaic Solar Cells

Current materials technology provides methods for reducing solar cell panel temperatures aboard spacecraft by passive heat dissipation technicues. Technology is available for the replacement of conventional solar cell panel substrates with materials which combine the advantages of lighter weight, improved structural strength, and increased thermal conductivity. This study demonstrates how the application of such methods can significantly improve the photovoltaic efficiency of solar cell panels.

Analysis of radiation damage in silicon by thermal annealing of solar cells

Abstract Thermal annealing of the photovoltaic parameters of silicon solar cells irradiated at room temperature by electrons (15 to 45 MeV), protons (5 MeV) and fast neutrons has been studied up to a temperature of 500 °C. The cells were prepared from single crystals grown by the Czochralski process (oxygen ∼1018/cm3) by the float-zone technique (oxygen ∼ 1016/cm3), each doped with boron or aluminum. The radiation damage was observed to anneal in two characteristic stages. The first stage occurs between 50° and 200°C and is independent of dopant type, of dopant concentration, and of the concentration of oxygen impurity. It is suggested that this stage is due to the breaking-up of clusters of recombination centers. In the second stage, observed between 275° and 450°C. the remaining damage produced by bombardment is removed. Unlike the low temperature stage, it is strongly dependent on the nature of the dopant and oxygen impurity concentration and bears a close resemblance to the annealing of 1-MeV electron...

Modulus of Rupture of zxt 45 ADP Crystals

The modulus of rupture (bending strength) of ammonium dihydrogen phosphate (ADP) of the zxt 45 orientation has been determined by the three‐point loading method. These measurements were performed with the aid of a breaking apparatus designed for the application of a constant loading rate commencing with the specimen in a zero‐load condition. The measured values of the modulus of rupture of 245–480 kg/cm2 with a mean of 340 kg/cm2 agree closely with figures previously reported for ADP crystals of arbitrary orientation. No significant variation of the modulus was observed for different crystal width to length ratios.