Study of (n,2n) reaction on 191,193Ir isotopes and isomeric cross section ratios

The cross section of 191 Ir(n,2n) 190 Ir g+m1 and 191 Ir(n,2n) 190 Ir m2 reactions has been measured at 17.1 and 20.9 MeV neutron energies at the 5.5 MV tandem T11/25 Accelerator Laboratory of NCSR “Demokritos”, using the activation method. The neutron beams were produced by means of the 3 H(d,n) 4 He reaction at a flux of the order of 2 × 10 5  n/cm 2 s. The neutron flux has been deduced implementing the 27 Al(n,α) reaction, while the flux variation of the neutron beam was monitored by using a BF3 detector. The 193 Ir(n,2n) 192 Ir reaction cross section has also been determined, taking into account the contribution from the contaminant 191 Ir(n,γ) 192 Ir reaction. The correction method is based on the existing data in ENDF for the contaminant reaction, convoluted with the neutron spectra which have been extensively studied by means of simulations using the NeusDesc and MCNP codes. Statistical model calculations using the code EMPIRE 3.2.2 and taking into account pre-equilibrium emission, have been performed on the data measured in this work as well as on data reported in literature.