Uniform convergence of exp integral

Question

I need to investigate a uniform convergence of the integral $I$ on E, where $$ I = \int_0^{+\infty} x^2 e^{-a x^4} \, \text{d} x, \, E = (0, \infty). $$ It's obvious for me that it converges uniformly on $E_{\beta}=(\beta, \infty), \beta > 0.$ I think on $E$ it converges, but not uniformly. How can I proof it?