Magnetization data on crystalline and polycrystalline MgB2, before and after irradiation with ~1MeV protons, were presented. In the virgin crystal, the critical current density was below the noise floor of 103A/cm2 over most of the field range. However, after irradiation a peak occurs in the current density as a function of applied magnetic field as the upper critical field HC2 was approached. After subsequent ageing over a time period of three months, the peak effect was greatly enhanced, exhibiting much stronger pinning over a wide field range, and the upper critical field was approximately doubled, accompanied by a 2K reduction in transition temperature. Similar studies were made of polycrystalline fragments, where irradiation led to an increased irreversibility field (JC was enhanced at high fields but decreased at low fields) and a suppression in transition temperature. However, after two years of ageing both parameters returned towards those of the virgin sample.

Effects of Proton Irradiation and Aging on the Superconducting Properties of Single Crystalline and Polycrystalline MgB2. G.K.Perkins, Y.Bugoslavsky, A.D.Caplin, J.Moore, T.J.Tate, R.Gwilliam, J.Jun, S.M.Kazakov, J.Karpinski, L.F.Cohen: Superconductor Science and Technology, 2004, 17, 232-5