Energy shifted level densities in rare earth region

The energy shift between the level densities of the even-odd and even-even isotopes ${}^{161,162}\mathrm{Dy}$ and ${}^{171,172}\mathrm{Yb}$ is measured as a function of excitation energy. The results are compared with predictions from various semiempirical models. The energy shift procedure works well for excitation energies between 3.5 and 7 MeV in the even-even nucleus, yielding a relative energy shift close to the experimental pairing gap parameter $\Delta .$