ISOSPIN MIXING IN THE NUCLEUS 60ZN

The isospin symmetry does not hold for the Coulomb interaction between protons in the nucleus. This leads to a breaking of the symmetry which induces a mixing between states with different values of isospin. This phenomenon is called isospin mixing and was measured in the N=Z nucleus 60Zn. The experiment was performed at Laboratori Nazionali di Legnaro (LNL) where the nucleus 60Zn, was formed by a fusion-evaporation reaction. The isospin mixing coefficients, at two temperatures T=2 MeV and T=2.4 MeV, were extracted from statistical model analyses of the E1 emission which should be forbidden for the selection rules of the symmetry. The probe we used was the GDR γ-decay. The isospin mixing for the ground state (T=0) was deduced from the values at finite temperature by using a temperature dependence theoretical model. The isospin mixing coefficient of the order of 2.5% was deduced and the measured value agrees with that from mass and beta decay measurements and with theory. These new data support the validity of this experimental technique based on the measurement of the GDR γ-decay in N=Z compound nuclei to give insight into the problem of isospin mixing. The value of isospin impurity is used for the estimation of the lifetime in Fermi beta decay. The isospin-symmetry-breaking correction δc used for the Fermi super-allowed transitions was also extracted.