Experimental study of the isovector giant dipole resonance in Zr 80 and Rb 81

Abstract

The isovector giant dipole resonance (IVGDR) γ decay was measured in the compound nuclei Zr80 and Rb81 at an excitation energy of E∗=54 MeV. The fusion reaction Ca40+Ca40 at Ebeam=136 MeV was used to form the compound nucleus Zr80, while the reaction Cl37+Ca44 at Ebeam=95 MeV was used to form the compound nucleus Rb81 at the same excitation energy. The IVGDR parameters extracted from the analysis were compared with the ones found at higher excitation energy (E∗=83 MeV). The comparison allows one to observe two different nuclear mechanisms: (i) the IVGDR intrinsic width remains constant with the excitation energy in the nucleus Rb81; (ii) the isospin-violating spreading width (i.e., Coulomb spreading width) remains constant with the excitation energy in the nucleus Zr80. The experimental setup used for the γ-ray detection was composed by the AGATA demonstrator array coupled to the large-volume LaBr3:Ce detectors of the HECTOR+ array.