As is known the fatigue strength of a metal is improved by understressing ~nd the cause has been attributed to the diffusion of foreign atoms to the tips of fatigue cracks.The authors however, wish to propose another explanation of the phenomen~ which strengthen a metal by understressing.Experimental results for steels indicate t?at two ,kinds of fat~e cracks are produced generally by cyclic stressmg; the one IS progressive and the other stationary. The strain distribution at [This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP: 155.33.16.124 On
The excess currents generated in anthracene crystals under x radiation have been measured as a function of x-ray intensity, electric field, and temperature. The currents were linear with respect to absorbed dose rate and electric field. A sensitivity of 7.1±0.7×10−12 C/cm2·rad at a field strength of 630 V/cm was obtained. The mobility, lifetime product, μτ, was 9.9±0.9×10−8 cm2/V. The photocurrent was observed to increase with increasing temperature and exhibited two different activation energies, one below 250°K and a second above 250°K. The magnitude of these energies decreased with increasing dose rate. The temperature behavior may be explained in terms of exciton theory or may be due to changes in carrier mobility.
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