Measurement of isospin mixing at a finite temperature in 80Zr via giant dipole resonance decay

Isospin mixing in the hot compound nucleus 80Zr was studied by measuring and comparing the γ-ray emission from the fusion reactions 40Ca+40Ca at Ebeam=200 MeV and 37Cl+44Ca at Ebeam=153 MeV. The γ yield associated with the giant dipole resonance is found to be different in the two reactions because, in self-conjugate nuclei, the E1 selection rules forbid the decay between states with isospin I=0. The degree of mixing is deduced from statistical-model analysis of the γ-ray spectrum emitted by the compound nucleus 80Zr with the standard parameters deduced from the γ decay of the nucleus 81Rb. The results are used to deduce the zero-temperature value, which is then compared with the latest predictions. The Coulomb spreading width is found to be independent of temperature.