Direct $^{157}$Gd($^3$He,$\alpha$2n)$^{154}$Gd reaction as a surrogate for $^{155}$Gd(n,2n)$^{154}$Gd

Recent work on the surrogate reaction method has shown that accurate neutron capture cross sections can be obtained with the right corrections to the angular momentum distribution in the compound nucleus. Many surrogate experiments use transfer reactions, which can bring more angular momentum than neutron absorption. This  can be corrected for, and in this work the experiment was set up to correct for the difference by decreasing the compound ($^3$He,$\alpha$) reactions. At the 88-inch Cyclotron at Lawrence Berkeley National Laboratory, $^{155}$Gd(n,2n) was studied using the surrogate reaction $^{157}$Gd($^3$He,$\alpha$2n). The STARS-LiBerAce detector system was used to detect forward-angle alphas and gammas de-exciting the $^{154}$Gd nuclei produced by the $^{157}$Gd($^3$He,$\alpha$2n) reaction.   Coincidences between the alphas and gammas were used to determine the probability of the excited $^{154}$Gd nucleus decaying to $^{156}$Gd. The optical model was used to calculate the total neutron cross section of $^{155}$Gd, and the probability of decay to $^{154}$Gd was converted into a $^{155}$Gd(n,2n) cross section, which compared favorably to a measurement between 6 and 14 MeV.