Diproton decay of nuclei on the proton drip line

The process of direct two-proton decay of nuclei with Z=22--28 on the proton drip line is considered. On the basis of new 0d3/2-0ff/2 shell-model mass extrapolations, ³⁹Ti, ⁴²Cr, ⁴⁵Fe, ⁴⁸Ni, and ⁴⁹Ni are found to be bound to single-proton decay but unbound to two-proton decay. New estimates of the spectroscopic factors and lifetimes have been made. The decays of ³⁹Ti, ⁴⁵Fe, and ⁴⁸Ni are found to be promising for further experimental investigation.