Measurement of the Neutron Cross Sections for the Reactions ¹⁶⁹Tm(n, 2n)¹⁶⁸Tm, ¹⁶⁹Tm(n,3n)¹⁶⁷Tm, and ¹⁸¹Ta(n,2n)^180mTa

The cross sections of the (n, 2n) reaction of ¹⁶⁹Tm and of ¹⁸¹Ta at 14.61 ± 0.31 MeV were determined relative to the known neutron cross section of the ²⁷Al(n, α)²⁴Na reaction. The resulting values are 2014 ± 93 and 1269 ± 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 ± 0.24 MeV, relative to the ¹⁶⁹Tm(n, 2n) cross section, to be 618 ± 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.