The anthrax incidents in the United States in the fall of 2001 led to the use of electron beam (EB) processing to sanitize the mail for the U.S. Postal Service. This method of sanitization has prompted the need to further investigate the effect of EB irradiation on the destruction of Bacillus endospores. In this study, endospores of an anthrax surrogate, B. atrophaeus, were destroyed to demonstrate the efficacy of EB treatment of such biohazard spores. EB exposures were performed to determine (i) the inactivation of varying B. atrophaeus spore concentrations, (ii) a D 10 value (dose required to reduce a population by 1 log 10 ) for the B. atrophaeus spores, (iii) the effects of spore survival at the bottom of a standardized paper envelope stack, and (iv) the maximum temperature received by spores. A maximum temperature of 49.2°C was reached at a lethal dose of ϳ40 kGy, which is a significantly lower temperature than that needed to kill spores by thermal effects alone. A D 10 value of 1.53 kGy was determined for the species. A surface EB dose between 25 and 32 kGy produced the appropriate killing dose of EB between 11 and 16 kGy required to inactivate 8 log 10 spores, when spore samples were placed at the bottom of a 5.5-cm stack of envelopes.

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Irradiation effects of 1-MeV electrons on InP-related materials such as InP, InGaP and InGaAsP have been examined in comparison with those of GaAs. Superior radiation-resistance of InP-related materials and their devices compared to GaAs has been found in terms of minority-carrier diffusion length and properties of devices such as solar cells and light-emitting devices. Moreover, minority-carrier injection-enhanced annealing of radiation-induced defects in InP-related materials has also been observed.

The development of new wide bandgap, highly radiation resistant semiconductors, such as Sic, may make it possible to use an inexpensive alpha particle emitting isotope to construct high efficiency, long lifetime radioisotope power sources. To study the possibility of producing an alphavoltaic battery, Sic photodetector diodes were irradiated with 5.5 MeV alpha particles from the radioisotope Am-241. Further studies of the radiation resistance of Sic were made using 1 MeV electrons in an accelerator facility. During the irradiation, the power output of the Sic cell was monitored and its degradation measured. Although the initial power output was considerable, a rapid decay of the power output occurred.Basic studies of the radiation resistance of Sic were also made! using deep level transient spectroscopy (DLTS). Six deep levels were found in both the unirradiated and irradiated Sic diodes. The carrier removal rate of 2.46 per 1 MeV electron measured here in Sic is very similar to the value of 2.85 per 1 MeV electron measured in InP, another highly radiation resistant semiconductor. The rapid degradation in output and considerable carrier removal rates observed here suggest that SIC has a radiation resistance similar to but not better than other radiation resistant semiconductors such as InP. The considerable initial output of the SIC battery was however, very encouraging, and further developments in SIC technology may make it possible to reduce the radiation damage rate in this application. In t ro d u c: t i o nThe maturation of new wide bandgap, highly radiation resistant semiconductors has made it worthwhile to revisit the topic of radioisotope batteries. SIC has a desirable combination of properties for radioisotope battery design, with a bandgap of 3 eV in the 6H polytype and a radiation induced atomic displacement threshold second only to diamond.(l) These attributes may make it possible to use an inexpensive alpha particle emitting isotope to construct higher efficiency, longer lifetime radioisotope batteries. These batteries are power sources for applications where neither solar nor chemical battery power are feasible.To simulate the operation of an alphavoltaic battery, Sic photodetector diodes were irradiated with 5.5 MeV alpha particles from the radioisotope Am-241. This isotope is inexpensive and widely available enough to be used in household smoke detectors, and has a long half life of 458 years. The operation of the SIC alphavoltaic battery is analogous to a solar cell with the exception of high energy particles impinging on the cell rather than light. Previous radioisotope battery designs were based on beta emitting isotopes such as Pm-147 and silicon diodes. (2) However, their performance was limited by the difficulty in absorbing all the energy of the high energy electron from the beta decay, the leakage current in the low bandgap Si diodes, the short lifetime of the isotope chosen and the radiation damage rate of the diodes. (3) Highly radiation resistant Sic semiconductor materials and...

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