Measurement of the neutron cross sections for the reactions 169Tm(n, 2n)168Tm, 169Tm(n, 3n)167Tm, and 181Ta(n, 2n) /sup 180m/ Ta

The cross sections of the (n, 2n) reaction of 169Tm and of 181Ta at 14.61 + or - 0.31 MeV were determined relative to the known neutron cross section of the 27Al(n, alpha)24Na reaction. The resulting values are 2014 + or - 93 and 1269 + or - 46 mb, respectively, when the Ryves et al. decay scheme is followed for the latter. The cross section of the (n, 3n) reaction of 169Tm was determined at 18.21 + or - 0.24 MeV, relative to the 169Tm (n, 2n) cross section, to be 618 + or - 25 mb. The shapes of the excitation curves for these three reactions were measured in the 12.3- to 18.3-MeV range. The (n, 2n) reactions were normalized at 14.61 MeV; the (n, 3n) reaction, at 18.21 MeV