The neutron-deficient neptunium isotopes ${}^{219,220}\mathrm{Np}$ were reinvestigated via the fusion-evaporation reaction ${}^{169}\mathrm{Tm}$(${}^{54}\mathrm{Cr}$, $3\text{−}4n$)${}^{219,220}\mathrm{Np}$ at the gas-filled recoil separator SHANS2 (Spectrometer for Heavy Atoms and Nuclear Structure-2). The $\alpha$-decay properties for these Np isotopes, which are the heaviest $N=126\mathrm{and}127$ isotones known to date, were measured with more statistics and improved precision. The ground-state $\alpha$ decay of ${}^{220}\mathrm{Np}_{127}$ with the $\alpha$-particle energy of $E_{\alpha }=10078\left(16\right)$ keV and the half-life of $T_{1/2}={23}_{-5}^{+9} \mu \mathrm{s}$ was updated. In the case of ${}^{219}\mathrm{Np}_{126}$, the improved decay data with $E_{\alpha }$ = 9015(16) keV and $T_{1/2}$ = $0.{14}_{-0.03}^{+0.07}$ ms were determined. In the framework of the Rasmussen method, the systematics of $\alpha$-decay reduced width match well with the previously known tendency with $N=126$. However, the new data may imply a difference in the influence of the $N=126$ shell effects beyond $Z=92$. In addition, the cross sections of the reaction were measured at several beam energies at the level of picobarns, exhibiting the promising capability of the SHANS2 separator to explore the boundary of the nuclear chart in the most neutron-deficient actinide region.

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• Alpha decay
• Lifetimes & widths
• Nuclear structure & decays
• 190 ≤ A ≤ 219
• A ≥ 220