Proton Nature of the Second Backbending nearN=90

The energy levels of the nuclei ${}_{}{}^{159}{}_{}{}^{}\mathrm{Tm}$ and ${}_{}{}^{157}{}_{}{}^{}\mathrm{Er}$ have been studied up to high spins ($\frac{61}{2}$ and $\frac{53}{2}$, respectively) and rotational frequencies (480 and 417 keV, respectively) by inbeam spectroscopic methods. On the basis of blocking arguments, the results show that the second backbending in the yrast band of even-even nuclei near $N=90\mathrm{}$ is due to $\pi h_{\frac{11}{2}}$ protons.