The effect of lattice damage caused by products of lΒ°B(n, a)VLi reactions and 235 U fissions at room temperature on the properties of bulk NbN and Nb(C, N) wires has been investigated. For both types of compounds the critical currents in transverse magnetic fields at 4.2 K show a sharp peak near H~2 which is increased by irradiation, whereas at low fields the critical currents are enhanced for Nb(C, N) but reduced for NbN. The upper critical field and the lattice parameter are slightly increased but no change in the transition temperature by irradiation was observed. The critical current behavior of Nb(C, N) samples was found to agree qualitatively with a flux pinning model developed by Kramer. 1
1. Introduction
Recent irradiation experiments 2 on superconductors with A-15 structure revealed considerable changes in the properties, especially critical currents, transition temperatures, and lattice parameters. The sensitivity of these materials to irradiation has mainly been explained by the chain structure of the A-15 compounds. These results suggest the importance of doing similar experiments on other type II superconductors with a different *Some of the results in this paper were presented at the International Discussion Meeting on