The effects of interrupted neutron irradiation on strain amplitude dependent internal friction in NaCl

Abstract

NaCl single crystals have been subjected to fast neutron irradiations during which the neutron beam was interrupted for a specific time interval. The variation of crystal decrement with strain amplitude (for strain amplitudes between 5*10-8 and 5*10-6) was measured at a series of times during the interrupted irradiations. Similar experiments were carried out at a number of temperatures between -16 and 22 degrees C. The results were analysed in terms of the theory of strain amplitude dependent internal friction developed by Granato and Lucke (1956). This theory yielded the variation with time in the number of pinning points added to each original dislocation loop. When the irradiation was interrupted, a decrease occurred in the pinning point number. This decrease reached completion within 1 minute at temperatures below 17 degrees C but required about 4 minutes to reach completion at higher temperatures. An explanation for this effect is offered which involves recombination of the pinning point parts.