The potential energy $(\mathrm{U})$ of a diatomic molecule is a function dependent on r (interatomic distance) as $\mathrm{U}=\frac{\alpha}{\mathrm{r}^{10}}-\frac{\beta}{\mathrm{r}^5}-3$ where, $\alpha$ and $\beta$ are positive constants. The equilibrium distance between two atoms will be $\left(\frac{2 \alpha}{\beta}\right)^{\frac{\mathrm{a}}{\mathrm{b}}}$, where $\mathrm{a}=$ $\_\_\_\_$ .