  It is shown that the proton formation probability, extracted from
experimental data corresponding to one-proton radioactivity, is divided into
two regions when plotted as a function of an universal parameter. This
parameter is derived from a microscopic description of the decay process. In
this way we explain the systematics of proton emission half-lives. At the same
time the formation probability is shown to be a useful quantity to determine
the deformation property of the mother nucleus.
