设 $\alpha_{1}, \alpha_{2}, \alpha_{3}$ 均为 3 维列向量, 记矩阵 $$ \boldsymbol {A} = \left(\boldsymbol {\alpha} _ {1}, \boldsymbol {\alpha} _ {2}, \boldsymbol {\alpha} _ {3}\right), \boldsymbol {B} = \left(\boldsymbol {\alpha} _ {1} + \boldsymbol {\alpha} _ {2} + \boldsymbol {\alpha} _ {3}, \boldsymbol {\alpha} _ {1} + 2 \boldsymbol {\alpha} _ {2} + 4 \boldsymbol {\alpha} _ {3}, \boldsymbol {\alpha} _ {1} + 3 \boldsymbol {\alpha} _ {2} + 9 \boldsymbol {\alpha} _ {3}\right). $$ 如果 $|\mathbf{A}| = 1$ ，那么 $|\mathbf{B}| =$