  We revisit the computation of the phase space factors (PSF) involved in the
positron decay and electron capture (EC) processes for a large number of nuclei
of experimental interest. To obtain the electron/positron wave functions needed
in computation, we develop a code for solving accurately the Dirac equation
with a nuclear potential derived from a realistic proton density distribution
in the nucleus. The finite nuclear size (FNS) and screening effects are
included through recipes which differ from those used in previous calculations.
Comparing our results with former calculations employing approximate methods
but computed with the same Q-values, we find a close agreement for positron
decays, while for the EC process there are relevant differences. For the EC
process we also find that the screening effect has a notable influence on the
computed PSF values specially for light nuclei. Further, we re-computed the
same PSF values but using the most recent Q-values reported in literature. In
several cases these new Q-values differ significantly from the older ones,
which results in large differences in the PSF values as compared with previous
results. These new PSF values proposed here, can contribute to a more reliable
calculation of the beta decay rates, which are key quantities in the study of
nuclei far from the stability line, as well as to better understanding of the
stellar evolution.
