  Sintered samples of MgB2 were irradiated in a fission reactor. Defects in the
bulk microstructure are produced during this process mainly by the 10B(n,a)7Li
reaction while collisions of fast neutrons with the lattice atoms induce much
less damage. Self-shielding effects turn out to be very important and lead to a
highly inhomogeneous defect distribution in the irradiated samples. The
resulting disorder enhances the normal state resistivity and the upper critical
field. The irreversibility line shifts to higher fields at low temperatures and
the measured critical current densities increase following irradiation.
