An Ne-like transient collisional excitation x-ray laser at 19.6nm (J = 0 → 1, 3p - 3s) was investigated numerically using a sophisticated hydrodynamic code for a l00μm thick Ge planar target irradiated by a nanosecond prepulse followed by a picosecond main optical laser pulse. The simulations indicate that for a given peak intensity,the main pulse has an optimal duration to generate the maximum effective gain. An effective gain as high as 200 cma-1 was obtained for the optimized drive pulse configuration.