The de Broglie wavelength for an electron accelerated through the potential difference of $$V_1$$ volt is $$\lambda_1$$. When the potential difference is changed to $$V_2$$ volt, the associated de Broglie wavelength is increased by 50%. If $$(V_1 / V_2) = (9 / \alpha)$$, then the value of $$\alpha$$ is __________.