Internal friction and modulus behaviour of gamma irradiated NaCl Crystals

Abstract

The internal friction and modulus of single crystals of Nad have been measured during the irradiation of the sample by 60Co gammas. Since the strain amplitude-independent internal friction is at present only explained in terms of the pinned dislocation theory, a test of the theory is important. The present investigation considers the time dependence of the decrement and modulus as a useful criterion for the validity of the theory. This follows from the loop length dependence of the decrement and ΔE/E. The generation of point defects during gamma irradiation results in the pinning of dislocation loops of the network due to the interaction between the point defects and dislocations. If we assume that n the number of pinning points is the sum of the number before and those produced during irradiation we have n = ʌ L = ʌ L 0 + at where L 0 is the loop length before irradiation and Λ is the total dislocation length per unit volume. A characteristic time dependence results during irradiation. Results will be discussed in terms of this model.