Slow Neutron Resonances in Holmium, Thulium, and Lutetium

The total cross sections of holmium, thulium, and lutetium have been measured over the neutron energy range from 0.1 to ∼30 ev. Resonances were found in ${\mathrm{Ho}}^{165}$ at 3.96, 12.8, 19, 22, and 39 ev; in ${\mathrm{Tm}}^{169}$ at 3.92 14.8, and 17.6 ev. Of the many resonances found in lutetium, the following tentative isotopic assignments have been made: ${\mathrm{Lu}}^{175}$—resonances at 5.30, 11.4, 14.4, 20.6, 24, and 31 ev; ${\mathrm{Lu}}^{176}$—resonances at 0.142, 1.57 2.62, and 4.80. It is probable that many additional resonances are present at higher energies in ${\mathrm{Lu}}^{176}$ but were not observed. The average spacing between resonances in ${\mathrm{Ho}}^{165}$, ${\mathrm{Tm}}^{169}$, and ${\mathrm{Lu}}^{175}$ (odd-even isotopes) is estimated to be of the same order of magnitude; i.e., respectively 10, 10, and 6 ev; while the spacing in ${\mathrm{Lu}}^{176}$ (odd-odd) appears to be much smaller, of the order of 1 to 2 ev. Parameters for several of the resonances have been obtained.