First Spectroscopy of the Near Drip-line Nucleus [superscript 40]Mg

Abstract

One of the most exotic light neutron-rich nuclei currently accessible for experimental study is ⁴⁰Mg, which lies at the intersection of the nucleon magic number <em>N</em>=28 and the neutron drip line. Low-lying excited states of ⁴⁰Mg have been studied for the first time following a one-proton removal reaction from ⁴¹Al, performed at the RIBF RIKEN with the DALI2 &gamma;-ray array and the Zero-Degree spectrometer. Two &gamma;-ray transitions were observed, suggesting an excitation spectrum that shows unexpected properties as compared to both the systematics along the <em>Z</em>=12, <em>N</em>&ge;20&thinsp;&thinsp;Mg isotopes and available state-of-the-art theoretical model predictions. A possible explanation for the observed structure involves weak-binding effects in the low-lying excitation spectrum.