Gamma decay of the giant dipole resonance and feeding of superdeformed states in 143Eu

The γ decay of the giant dipole resonance (GDR) built on excited nuclear states has been measured in coincidence with the low-energy γ discrete transitions for the nucleus ¹⁴³Eu. The reaction used was ¹¹⁰Pd(³⁷Cl, 4n)¹⁴³Eu at a beam energy of 165 MeV. The EUROBALL spectrometer (for the measurement of discrete γ transitions) coupled with the HECTOR array (for high-energy γ-ray detection) has been used. The high-energy γ-ray spectrum in coincidence with superdeformed (SD) discrete transitions of ¹⁴³Eu shows an “excess” between 9–12 MeV if compared with the one associated to cascades which do not pass through the SD configurations. Such an “excess” is in the energy region where one expects the low-energy component of the GDR strength function built on a SD state. The measured intensity can be reproduced by the statistical model assuming that the superdeformation survives only few MeV above the yrast line. A similar and consistent scenario has also been obtained by comparing the high-energy γ-ray spectra of ¹⁴³Eu in coincidence with its spherical (which is fed by the SD configuration) and its triaxial configuration (which is bypassed by the decay of the SD states).