Search for low lying dipole strength in the neutron rich nucleus $^{26}$Ne

TL;DR

This study investigates low-lying dipole strength in the neutron-rich nucleus $^{26}$Ne using Coulomb excitation, revealing a pygmy resonance around 9 MeV with measurable E1 strength, and provides the first decay pattern analysis of such states.

Contribution

It presents the first decay pattern analysis of low-lying dipole strength in a neutron-rich nucleus, identifying a pygmy resonance around 9 MeV.

Findings

Observed E1 strength between 6 and 10 MeV

Confirmed E1 nature through angular distribution

Measured B(E1)=0.49±0.16 e^2fm^2

Abstract

Coulomb excitation of the exotic neutron-rich nucleus $^{26}$Ne on a $^{nat}$Pb target was measured at 58 A.MeV in order to search for low-lying E1 strength above the neutron emission threshold. Data were also taken on an $^{nat}$Al target to estimate the nuclear contribution. The radioactive beam was produced by fragmentation of a 95 A.MeV $^{40}$Ar beam delivered by the RIKEN Research Facility. The set-up included a NaI gamma-ray array, a charged fragment hodoscope and a neutron wall. Using the invariant mass method in the $^{25}$Ne+n channel, we observe a sizable amount of E1 strength between 6 and 10 MeV. The reconstructed $^{26}$Ne angular distribution confirms its E1 nature. A reduced dipole transition probability of B(E1)=0.49$\pm$0.16 $e^2fm^2$ is deduced. For the first time, the decay pattern of low-lying strength in a neutron-rich nucleus is obtained. The results are discussed in terms of a pygmy resonance centered around 9 MeV.