Experimental confirmation of the low B isotope coefficient of MgB2

Recent investigations have shown that the first proposed explanations of the disagreement between experimental and theoretical values of isotope coefficient in MgB2 need to be reconsidered. Considering that in samples with residual resistivity of few mu Omega cm critical temperature variations produced by disorder effects can be comparable with variations due to the isotopic effect, we adopt a procedure in evaluating the B isotope coefficient, which takes account of these effects, obtaining a value, which is in agreement with previous results, and then confirming that there is something still unclear in the physics of MgB2.