Influence of protons on backbending

Backbending in (at least the first half of) the rare earth nuclei seems to be determined by the alignment of an $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ neutron pair. This is supported by the disappearance of backbending due to the blocking of an $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ level by an odd neutron for example in ¹⁶⁵Yb. Contrary to expectations backbending disappears also by adding an odd $\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$,proton to ₇₀¹⁶⁶Yb in ₇₁¹⁶⁷Lu for this state (but is present if the odd proton is in the $\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ level). A theory is presented which explains the odd neutron and the odd proton nuclei. It turns out that the odd proton in ¹⁶⁷Lu serves only as a type of catalyst for the alignment of an $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ neutron pair. The odd proton changes the deformation and moves the Fermi surface nearer ($\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$) or farther away ($\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$) from the nearest $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ neutron level. In one case one finds backbending and in the other case no backbending in ¹⁶⁷Lu.