Particle-Hole Cluster Shell Model States in ⁸Be, a Challenge for Ab-Intio Nuclear Theories

LNS at Avery Point, University of Connecticut, 1084 Shennecossett Rd, Groton, CT 06340, USA

^* e-mail: moshe.gai@uconn.edu

Published online: 4 December 2019

Abstract

We propose the first application of the Cluster Shell Model (CSM) of Della Rocca and Iachello to particle-hole (p-h) states in ⁸Be. We demonstrate a few essential features of the CSM in ⁸Be: 1) All predicted p-h states of the CSM, and only the predicted p-h states, are observed near thresholds and up to 19.5 MeV in ⁸Be. 2) The states are observed in the predicted order, with positive parity states below negative parity states. 3) Some of the p-h states are already known to have the rotational structure predicted for the deformed p-h states. 4) The rotational structures observed at high excitations in the p-h bands in ⁸Be, resemble the ground state bands of ⁸Be, ⁹Be and ⁹B, with similar moment of inertia. Based on these observations we contemplate new measurements of the spectroscopy of ⁸Be at energies above 19.5 MeV, where our knowledge of states in ⁸Be is scarce. We examine the observed B(M1)s and B(E2)s in these nuclei and contemplate a measurement of the B(E2) of the isobaric Analog transition in ⁸B. We discuss the observed rotational structure in ⁸Be as a challenge to ab-initio calculations that searched for “emerging rotational structures at high excitations" in beryllium nuclei, and reveal rotational structure at high excitations in ¹⁰Be and ¹²Be but not in ⁸Be.