α Decay Studies on New Neutron-deficient Np Isotopes

In contemporary nuclear research field, it is of special interest to synthesize the new isotopes far from the stability line and to explore the existing limit of nuclei. For the most proton-rich N≈126 isotones, which are located near the crossing point between the proton drip line and the N=126 closed shell, synthesizing and α-decay studies may shed new light on the structural evolution of the N=126 shell closure. Based on measurements at the gas-filled recoil separator SHANS, the most neutron-deficient new isotopes, ^{219,220,223,224}Np, were synthesized via ^36,40Ar+^185,187Re fusion-evaporation reactions. The new experimental results allow us to establish the α-decay systematics for Np isotopes around N=126 for the first time, and to test the robustness of this shell closure in neptunium. The systematic analysis of single proton separation energies figures out the exact location of the proton drip line in Np isotopic chain. At the same time, the isotope ²¹⁹Np was identified as the presently known heaviest nuclide beyond the proton drip line. In addition, the possibility of producing other new isotopes (^218,221,222Np) in this region is discussed in terms of the measured cross sections and the theoretical predictions.