Effects of Carbon Doping and Neutron Irradiation on MgB2

We have irradiated Mg(B$_{0.962}$C$_{0.038}$)$_2$ with thermal neutrons and performed post exposure annealing studies to probe the interplay between two different sources of defects. Carbon is believed to act as a point defect, enhancing H$_{c2}$ due to an increase in scattering in the $\pi$ band, without significantly enhancing flux pinning. Neutron damage studies on pure MgB$_2$ wire segments show a suppression of H$_{c2}$ that approximately scales with T$_c$, and an increase in the critical current density at low fields. Irradiation of carbon doped fibers results in a similar scaling of the enhanced H$_ {c2}$ with T$_c$, and the cumulative effects enhance J$_c$ at intermediate fields.