Half-lives and presupernova weak interaction rates for nuclei away from the stability line

A detailed model for the calculation of -decay rates of the fp shell nuclei for situations prevailing in presupernova and collapse phases of evolution of the core of massive stars leading to supernova explosion has been extended for electron-capture rates. It can also be used to determine the half-lives of neutron-rich nuclei in the fp/fpg shell. The model uses an averaged Gamow-Teller (GT) strength function, but it can also use the experimental log ft values and GT strength function from (n, p) reaction studies wherever available. The calculated rate includes contributions from each of the low-lying excited states of the mother including some specific resonant states (`back resonance') having large GT matrix elements.