Abstract
Low-frequency (350 Hz) permeability measurements at 4.2°K using phase-sensitive techniques were carried out on a Nb sample irradiated in the Oak Ridge Research Reactor at 40°C to several fast neutron doses up to 6×1019 neutrons/cm2 (E> 1 MeV). In the mixed-state region a signal proportional to the electromagnetic loss in the sample is observed which decreases with increasing fast neutron dose. Quantitative estimates of the power dissipation in irradiated Nb are given which are then related to the magnetic field dependence of the critical current density Jc(H).