  We report the results of studying the influence of the uranium-ion
irradiation of the Bi_2Sr_2CaCu_2O_8 thin films on the high-temperature part
(close to critical temperature) of their irreversibility line. We studied
irreversible properties of the films by measuring the hysteresis of nonresonant
microwave absorption. The results have revealed the shift of irreversibility
line towards low temperatures and magnetic fields. The effect is most
significant for the films irradiated with large doses, more than 1T. This fact
is in good agreement with the theoretical prediction by Koshelev and Vinokur of
suppression of surface barrier by columnar defects.
