Energy Levels of Tm

Abstract

Fifty-one levels in Tm 168 have been observed up to an excitation energy of 1514 keV utilizing 12-MeV deuterons and the reaction Tm 169 (d, t)Tm 168 . The Q value of the lowest observed state was determined to be −1776 ± 15 keV. The spectrum below 700 keV has been interpreted in terms of the coupling of the [411↓] Nilsson proton orbital with the neutron orbitals prominent in the low-energy (d, t) spectrum of Er 167 . This interpretation has resulted in the determination of relative energies due to the residual neutron—–proton interaction for six different configurations. The observed singlet—–triplet splitting energies for the [633↑], [521↓], and [512↑] neutron orbitals coupled to the [411↓] proton orbital were measured to be −157, +191, and −234 keV, respectively. Theoretical calculations of these energies made for a zero range spin-dependent central potential gave values of −87, +154, and −255 keV, respectively. The good agreement indicates that the spin—–spin interaction can account for most of the singlet—–triplet splitting energy.