We have studied the effect of damage induced by 2 MeV alpha particles on the critical temperature, T c , and resistivity, , of MgB 2 thin films. This technique allows defects to be controllably introduced into MgB 2 in small successive steps. T c decreases linearly as the intragrain resistivity at 40 K increases, while the intergrain connectivity is not changed. T c is ultimately reduced to less than 7 K and we see no evidence for a saturation of T c at about 20 K, contrary to the predictions of the T c of MgB 2 in the dirty limit of interband scattering.

a) J. Kim, a) B. Wilkens, b) N. Newman, a),b),g) J.M. Rowell, a) A.V. Pogrebnyakov, c),d),e) X.X. Xi, c),d),e) J.M. Redwing, d),e) S.Y. Xu, c),e) Qi Li, c),e) and B.H. Moeckly f)

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