Irradiation effects on MgB2 bulk samples and formation of columnar defects in high-Tc superconductor

Irradiation effects on MgB2 were studied to investigate the pinning property of this new material. It is pointed out that flux pinning at grain boundaries is important for MgB2 bulk samples. We confirmed this with electron irradiation. Degradation of inter-grain coupling by electron irradiation resulted in degradation of pinning properties. Heavy ion irradiation was also accomplished on MgB2. Columnar defects introduced by the irradiation improve pinning in higher field regions. Concerning the formation of columnar defects in high-T-c superconductors, we conducted a systematic analysis of Bi2212 single crystal with different irradiation ions. Applying the time dependent line source model to our results, only a third of the electronic losses contributed to the formation of columnar defects. (C) 2002 Elsevier Science B.V. All rights reserved.