New $\alpha$-Emitting Isotope ${}^{214}$U and Abnormal Enhancement of $\alpha$-Particle Clustering in Lightest Uranium Isotopes

Abstract

A new $\alpha$-emitting isotope ${}^{214}$U, produced by fusion-evaporation reaction ${}^{182}$W(${}^{36}$Ar, 4n)${}^{214}$U, was identified by employing the gas-filled recoil separator SHANS and recoil-$\alpha$ correlation technique. More precise $\alpha$-decay properties of even-even nuclei ${}^{216,218}$U were also measured in reactions of ${}^{40}$Ar, ${}^{40}$Ca with ${}^{180,182,184}$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 magic neutron number $N=126$ were deduced. Their systematic trends are discussed in terms of $N_p{N}_n$ 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 ${}^{214,216}$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 a large-scale shell model calculation.

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