Isovector soft dipole mode in 6Be

TL;DR

This study investigates the continuum states of 6Be up to 16 MeV using charge-exchange reactions, revealing a novel isovector soft dipole mode that dominates the reaction mechanism and provides new insights into nuclear excitations.

Contribution

First observation of the isovector soft dipole mode in 6Be, demonstrating its dominance in charge-exchange reactions and expanding understanding of nuclear excitation modes.

Findings

Identified a broad structure from 4 to 16 MeV in 6Be spectrum.

Observed the isovector soft dipole mode as a dominant excitation mechanism.

Found that this mode accounts for about 60% of the reaction cross section.

Abstract

By using the 1H(6Li,6Be)n charge-exchange reaction, continuum states in 6Be were populated up to E_t=16 MeV, E_t being the 6Be energy above its three-body decay threshold. In kinematically complete measurements performed by detecting alpha+p+p coincidences, an E_t spectrum of high statistics was obtained, containing approximately ~5x10^6 events. The spectrum provides detailed correlation information about the well-known 0^+ ground state of 6Be at E_t=1.37 MeV and its 2^+ state at E_t=3.05 MeV. Moreover, a broad structure extending from 4 to 16 MeV was observed. It contains negative parity states populated by Delta L=1 angular momentum transfer without other significant contributions. This structure can be interpreted as a novel phenomenon, i.e. the isovector soft dipole mode associated with the 6Li ground state. The population of this mode in the charge-exchange reaction is a dominant phenomenon for this reaction, being responsible for about 60% of the cross section obtained in the measured energy range.