The even-Z odd-N neutron-halo nuclei, which are the possible lightest neutron-halo nuclei heavier than $^{ 37}$Mg, are explored by studying the shell-structure unique in weakly-bound neutrons for spherical or deformed shape. It is pointed out that due to the narrowed N=50 spherical energy-gap and a few resulting close-lying neutron one-particle levels, 1g$_{ 9/2}$, 3s$_{ 1/2}$, and 2d$_{ 5/2}$, for spherical shape, nuclei with some weakly-bound neutrons filling in those levels may be deformed and have a good chance to show deformed s-wave halo. Promising candidates are $^{ 71}_{ 24}$Cr$_{ 47}$, $^{ 73}_{ 24}$Cr$_{ 49}$, $^{ 75}_{ 24}$Cr$_{ 51}$ and $^{ 77}_{ 26}$Fe$_{ 51}$ in the case that those nuclei lie inside the neutron drip-line. An interesting possibility of the deformed p-wave or s-wave halo is suggested also for the nucleus $^{ 53}_{ 18}$Ar$_{ 35}$.
Categories: nucl-th