Abstract
By using the 1H(6Li, 6Be)n charge-exchange reaction, population of continuum states in 6Be was observed up to ET=16 MeV, ET being the 6Be energy above its three-body decay threshold. In kinematically complete measurements performed by detecting α+p+p coincidences, an ET spectrum of high statistics was obtained, containing approximately ∼5×106 events. The spectrum provides detailed correlation information about the well-known 0+ ground state of 6Be at ET=1.37 MeV and its 2+ state at ET=3.05 MeV. Moreover, a broad structure extending from 4 to 16 MeV was observed. It contains negative parity states populated by ΔL=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.
Highlights
IntroductionElectromagnetic excitation is an important tool for studying light exotic (halo) nuclei
Electromagnetic excitation is an important tool for studying light exotic nuclei
We identified the properties of the 6Be continuum above the highest-lying well-established state, i.e. the 2+ state at ET = 3.03 MeV, ET being the 6Be energy above its three-body decay threshold
Summary
Electromagnetic excitation is an important tool for studying light exotic (halo) nuclei. Based on the halo hypothesis, the existence of a novel dipole mode at low excitation energies was predicted [ 1, 2, 3]. The low binding allows low-frequency oscillations of the halo nucleon(s) against the core, creating the low-lying dipole excitations and providing abnormally large cross-sections for electromagnetic dissociation at low-energy. Experiments confirmed these expectations [ 4, and Refs. Therein] and showed that the observed low-lying E1 strength is in a good agreement with the cluster non-energy-weighted sum rule The latter observation indicates that the SDM is connected with the cluster degrees of freedom in contrast with excitations in the GDR region, which represent collective phenomena. The fact that 6Be is an isobaric partner of the “classical”
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
