A new $\alpha$-emitting isotope ${}^{214}\mathrm{U}$, produced by the fusion-evaporation reaction ${}^{182}\mathrm{W}({}^{36}\mathrm{Ar},4\mathrm{n}){}^{214}\mathrm{U}$, was identified by employing the gas-filled recoil separator SHANS and the recoil-$\alpha$ correlation technique. More precise $\alpha$-decay properties of even-even nuclei ${}^{216,218}\mathrm{U}$ were also measured in the reactions of ${}^{40}\mathrm{Ar}$, ${}^{40}\mathrm{Ca}$ beams with ${}^{180,182,184}\mathrm{W}$ targets. By combining the experimental data, improved $\alpha$-decay reduced widths ${\delta }^2$ for the even-even Po-Pu nuclei in the vicinity of the magic neutron number $N=126$ are deduced. Their systematic trends are discussed in terms of the $N_p{N}_n$ scheme in order to study the influence of proton-neutron interaction on $\alpha$ decay in this region of nuclei. It is strikingly found that the reduced widths of ${}^{214,216}\mathrm{U}$ are significantly enhanced by a factor of two as compared with the $N_p{N}_n$ systematics for the $84\le Z\le 90$ and $N<126$ even-even nuclei. The abnormal enhancement is interpreted by the strong monopole interaction between the valence protons and neutrons occupying the $\pi 1f_{7/2}$ and $\nu 1f_{5/2}$ spin-orbit partner orbits, which is supported by the large-scale shell model calculation.

The new thorium isotope ${}^{207}\mathrm{Th}$ has been produced in the $5n$ evaporation channel of the fusion reaction ${}^{36}\mathrm{Ar}+{}^{176}\mathrm{Hf}$. It was separated in flight by the gas-filled recoil separator SHANS and identified on the basis of a correlated $\alpha$-decay chain. The $\alpha$ decay of ${}^{207}\mathrm{Th}$, measured with an $\alpha$-particle energy of 8167(21) keV and a half-life of $9.7_{-4.4}^{+46.6}$ ms, is assigned to originate from ground state. By combining with existing data, we find that the $\alpha$-decay energies of nuclei with $Z>82$ and $N<126$ show a regular and distinct odd-even staggering (OES) rather than the commonly supposed smooth pattern. A theoretical analysis has been performed within relativistic Hartree-Fock-Bogoliubov and large-scale shell-model approaches. It is found that the OES originates from both pairing correlations and blocking of particular orbitals by unpaired nucleons. Of particular importance is that pairing correlations result in the OES not only through the contribution of pairing energy to binding energy, but also by configuration mixing induced by scattering nucleons to orbitals away from Fermi levels.

Background: The properties of nuclei located in the region “south” of ${}^{208}\mathrm{Pb}$ are important for understanding the $r$-process nucleosynthesis. While some isomeric states and their spectroscopic properties have been investigated experimentally in neutron-rich Pb, Tl, and Hg isotopes recently, a large portion of the area still remains unreachable.

To investigate the underlying mechanisms responsible for the enhanced production of new neutron-rich $N\approx 126$ nuclei in the reaction ${}^{238}\mathrm{U}+{}^{198}\mathrm{Pt}$, detailed simulations of the system at an incident energy of 8 MeV/nucleon using the improved quantum molecular dynamics model have been performed. Sequential and massive transfer processes, responsible for the production of targetlike and projectilelike $n$-rich $N\approx 126$ fragments, respectively, have been recognized. Compared to sequential transfer, the contribution from the massive transfer process plays an almost equal role for the production of new nuclei with atomic number $Z\le 76$. The two processes show distinct features in the angular and kinetic energy distributions in the laboratory system and hopefully can be disentangled experimentally.