A particle of mass m moves in a circular orbit in a central potential field U(r)=U_0 r^4. If Bohr's quantization conditions are applied, radii of…

A particle of mass $\displaystyle m$ moves in a circular orbit in a central potential field $\displaystyle U(r)=U_0 r^4$. If Bohr's quantization conditions are applied, radii of possible orbitals $\displaystyle r_n$ vary with $\displaystyle n^{\frac{1}{\alpha}}$, where $\displaystyle \alpha$ is \_\_\_\_.