Low-energy modification of the gamma strength function of the odd-even nucleus In-115

Abstract : Photoactivation yield measurements on 115 In have been performed at the ELSA facility with Bremsstrahlung photon beams over a range of endpoint energies between 4.5 and 18 MeV. The measured photoexcitation yields of the 115m In metastable state are compared with calculated yields using cross sections obtained with different models of the photon strength function. It is shown that additional photon strength with respect to the general Lorentzian model is needed at 8.1 MeV for the calculated yields to reproduce the data. The origin of this extra strength is unclear, because it is compatible with additional strength predicted in both E1 and M1 photon strength distributions by quasiparticle random-phase approximation calculations using the Gogny D1S force.