Neutron Total Cross Sections in the 17- to 29-Mev Region

The neutron total cross sections of 42 elements and isotopes were measured at several energies between 17 and 29 Mev using monoenergetic neutrons produced by the Livermore variable-energy cyclotron through the $\mathrm{T}(d, n){\mathrm{He}}^4$ reaction. Beam contaminations by gamma rays and low-energy "breakup" neutrons were measured by time-of-flight techniques, and their effects were kept small by suitably high bias on the plastic scintillator detector. The accuracy in cross section is typically ±1 to 2%. The data in this energy region have been sparse heretofore. Where comparisons with previous data have been possible, there is substantial agreement. When plotted versus energy and mass number, the data form a smooth cross-section surface which joins on smoothly to the data at lower energies. The data seem in good agreement with the predictions of the optical model of Bjorklund and Fernbach.