If the mass number of nucleus is $\alpha$, its radius is $R _ { \alpha }$. And another mass number is $\beta$ then its radius is $\mathrm { R } _ { \beta }$; then $\mathrm { R } _ { \alpha } / \mathrm { R } _ { \beta } =$ ?
[Given $\beta = \mathbf { 8 } \boldsymbol { \alpha }$ ]
(A) 1
(B) $1 / 2$
(C) $1 / 3$
(D) 2