Nature of low-lying electric dipole resonance excitations in 74Ge

TL;DR

This study investigates the isospin properties of low-lying electric dipole excitations in 74Ge, revealing a split in excitation regions and confirming theoretical predictions about isoscalar and isovector contributions.

Contribution

It provides new experimental evidence for the splitting of dipole excitation regions and compares these findings with advanced RQTBA theoretical calculations.

Findings

Dipole excitations split into two regions at 6-9 MeV

Low-energy region excited by both isoscalar and isovector probes

High-energy region excited only by electromagnetic probe

Abstract

Isospin properties of dipole excitations in 74 Ge are investigated using the ({\alpha},{\alpha}'{\gamma}) reaction and compared to ({\gamma},{\gamma}) data. The results indicate that the dipole excitations in the energy region of 6 to 9 MeV adhere to the scenario of the recently found splitting of the region of dipole excitations into two separated parts: one at low energy, being populated by both isoscalar and isovector probes, and the other at high energy, excited only by the electromagnetic probe. Relativistic quasiparticle time blocking approximation (RQTBA) calculations show a reduction in the isoscalar E1 strength with an increase in excitation energy, which is consistent with the measurement.