An advanced type of Nb3Sn composite wire was irradiated at sim;6 K with fast neutrons. The shorthyphen;section critical currentjcwas measured at 4.2 K (after annealing to 77 K) in transverse magnetic fields up to 10 T. Before irradiation,jcat 4 T was 1.6times;106A/cm2. A fluence of 1.8times;1018n/cm2increasedjcforHgsim;2T, the enhancement increasing with field to 85percnt; atH=10 T. After annealing to 540 K, roughly onehyphen;half the enhancement remained. These results are compared with those for an earlier similar material, but with a smallerjcbefore irradiation. For comparable fluences, the relative enhancement in the earlier material was unexpectedly less than in the improved samples.
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