Abstract : We carried out the Coulomb excitation, on a lead target, of an exotic beam of neutron-rich nucleus 26Ne at 58 A.MeV, in order to study the possible existence of a pygmy dipole resonance above the neutron emission threshold. The experiment was performed at the RIKEN Research Facility, in Tokyo (Japan) and included a gamma-ray detector, a charged fragment hodoscope and a neutron detector.
Using the invariant mass method in the 25Ne+n decay channel, and by comparing the reaction cross section on the lead target and a light target of aluminium, we observe a sizeable amount of E1 strength between the one neutron and the two neutron emission thresholds. The corresponding 26Ne angular distribution confirms its nature and we deduce its reduced dipole transition probability value B(E1) = 0.54 (0.18) e2fm2. Our method also enables us to extract for the first time the decay pattern of a pygmy resonance.
By detecting the decay photons from the excited states below the neutron emission threshold and by analyzing the angular distribution of the inelastically scattered 26Ne we deduce the reduced transition probability of the first 2+ state, from the ground state. The value obtained of B(E2) = 87 (13) e2fm4
Being in disagreement with a previous result.