Measurements of Gap Anistropy inA15Nb3Sn

A recent suggestion by Farrell and Chandrasekhar that a major part of the critical-temperature ($T_c$) reduction in $A15\mathrm{}$ superconductors, caused by radiation-induced defects, is a manifestation of a large gap anisotropy is examined for ${\mathrm{Nb}}_3$Sn. Electron-irradiation data show that the $T_c$ changes with damage are inconsistent with a large gap anisotropy. However, if one assumes that the initial changes in $T_c$ with fluence are indeed due to gap anisotropy, then it is shown that the anisotropy parameter $〈a^2〉$ for ${\mathrm{Nb}}_3$Sn is ≲ 0.03.