Short-Lived <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>α</mml:mi></mml:math>-Emitting Isotope <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>Np</mml:mi></mml:mrow><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>222</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:math> and the Stability of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>N</mml:mi><mml:mo>=</mml:mo><mml:mn>126</mml:mn></mml:math> Magic Shell

Abstract

A new, very short-lived neutron-deficient isotope $^{222}\mathrm{Np}$ was produced in the complete-fusion reaction $^{187}\mathrm{Re}(^{40}\mathrm{Ar},5\mathrm{n})^{222}\mathrm{Np}$, and observed at the gas-filled recoil separator SHANS. The new isotope $^{222}\mathrm{Np}$ was identified by employing a recoil-$\ensuremath{\alpha}$ correlation measurement, and six $\ensuremath{\alpha}$-decay chains were established for it. The decay properties of $^{222}\mathrm{Np}$ with ${E}_{\ensuremath{\alpha}}=10016(33)\text{ }\text{ }\mathrm{keV}$ and ${T}_{1/2}=38{0}_{\ensuremath{-}110}^{+260}\text{ }\text{ }\mathrm{ns}$ were determined experimentally. The $\ensuremath{\alpha}$-decay systematics of Np isotopes is improved by adding the new data for $^{222}\mathrm{Np}$, which validates the $N=126$ shell effect in Np isotopes. The evolution of the $N=126$ shell closure is discussed in the neutron-deficient nuclei up to Np within the framework of $\ensuremath{\alpha}$-decay reduced width.