Measurements of delayed neutrons yields and time spectra from 1 GeV protons interacting with thick natPb, 209Bi and natFe targets

This paper presents the experimental results on the delayed neutrons (DN) yields and time spectra from 1 GeV protons interacting with natural lead, 209Bi and natural iron targets of variable thicknesses from 5 cm to 55 cm. Both absolute yields and time constants were obtained. In parallel, the MCNPX and PHITS codes were used to predict the DN precursors and construct the theoretical DN tables. Different model parameters are examined and show significant dependence on the choice of the intra-nuclear cascade and fission-evaporation models used. These data and modelling are of great importance for the new generation spallation neutron sources based on liquid metal technologies. Finally, the above experiment allowed the determination of the production cross sections of a number of delayed neutrons precursors as, 87Br, 88Br and 17N. For the 3 targets the emission of delayed neutrons is dominated by light reaction products such as 9Li and 17N during decay times from 0 to 20-30 s. In the case of fissile targets after longer decay times the fission fragments such as 88Br and 87Br are the major contributors. These results permit the examination of two different reaction mechanisms, namely fission and fragmentation, implemented in high energy transport codes. (authors)