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

Moshe Gai

doi:10.1051/epjconf/201922301019

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.

Highlights

The nuclei 12C and 8Be have currently attracted much attention
On one hand the algebraic cluster model (ACM) of Bijker and Iachello [1], presents some of the most interesting application of geometrical point group symmetries to cluster states, and on the other hand ab-initio theories such as the no-core shell model (NCCI) [2] and the quantum Monte Carlo (GFMC) [3], can be applied to these light nuclei as testing grounds
We identified a rotational structure in 8Be at very high excitations above 16 MeV

Summary

Introduction

The nuclei 12C and 8Be have currently attracted much attention. On one hand the algebraic cluster model (ACM) of Bijker and Iachello [1], presents some of the most interesting application of geometrical point group symmetries to cluster states, and on the other hand ab-initio theories such as the no-core shell model (NCCI) [2] and the quantum Monte Carlo (GFMC) [3], can be applied to these light nuclei as testing grounds. Perhaps one of the most intriguing aspect of these new theoretical development is the prediction and observation in 12C of the mixed parity ground state rotational band including the 4+ and 4− parity doublet, and the states of Jπ = 0+, 2+, 3−, 4± and 5− [4]

Ab-Initio No Core Shell Model

The Cluster Shell Model

CSM p-h states in 8Be

Conclusions