Effect of columnar defects on reversible magnetization of superconducting

(Formula presented)-axis-oriented superconducting (Formula presented) (Bi-2223) tapes have been irradiated with 5.8-GeV Pb ions to produce columnar defects along the (Formula presented) axis. The magnetization (Formula presented) as a function of field and temperature were measured for both the unirradiated and irradiated samples at matching field (Formula presented) values of 1.28, 2.0, and 4 T. In striking contrast to the conventional (Formula presented) dependence of the reversible (Formula presented) in the London regime, the field dependence of the reversible (Formula presented) for the irradiated samples exhibits some unusual characteristics. A large reduction in the value of (Formula presented) was observed at (Formula presented), while a maximum appears at (Formula presented). We explain this field dependence in terms of the London model modified by the localization of the vortex lines in the columnar defects. Based on this study, we obtained the single vortex pinning energy for Bi-2223 by these columnar defects.