DILEPTON AND PHOTON DECAY OF GIANT-RESONANCES BUILT ON EXCITED-STATESOF NI-56

Nuclear states in Ni-56, at an initial excitation energy E=70 MeV, we re populated via the isospin T=0 reaction O-16+Ca-40. The dilepton- (e (+)e(-)) pairs and photon-decay yields were measured simultaneously. S tatistical decay calculations describe well both measurements on an ab solute scale. The isospin mixing parameter extracted from these measur ements (alpha(2)=0.065) is consistent with other studies of the isospi n symmetry in highly excited compound nuclei. The 1 sigma upper limit for the observed monopole strength is 4.3 nb, which is 3 times higher than the one sum rule value calculated with the statistical model for the decay of the compound nucleus.