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

Isospin mixing in the hot compound nucleus Zr-80 was studied by measuring and comparing the gamma-ray emission from the fusion reactions Ca-40 + Ca-40 at E-beam = 200 MeV and Cl-37 + Ca-44 at E-beam = 153 MeV. The gamma 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 gamma-ray spectrum emitted by the compound nucleus Zr-80 with the standard parameters deduced from the gamma decay of the nucleus Rb-81. 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.