New α -Emitting Isotope 214U and Abnormal Enhancement of α -Particle Clustering in Lightest Uranium Isotopes

A new α -emitting isotope ²¹⁴U, produced by the fusion-evaporation reaction ¹⁸²W (³⁶Ar,4 n )²¹⁴U, was identified by employing the gas-filled recoil separator SHANS and the recoil-α correlation technique. More precise α -decay properties of even-even nuclei ^U,218₂₁₆ were also measured in the reactions of ⁴⁰Ar, ⁴⁰Ca beams with ^180,182,184W targets. By combining the experimental data, improved α -decay reduced widths δ² 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_pN_n scheme in order to study the influence of proton-neutron interaction on α decay in this region of nuclei. It is strikingly found that the reduced widths of ^U,216₂₁₄ are significantly enhanced by a factor of two as compared with the N_pN_n systematics for the 84 ≤Z ≤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 π 1 f_{7 /2} and ν 1 f_{5 /2} spin-orbit partner orbits, which is supported by the large-scale shell model calculation.