As said in chapter 4, the CERN FEAT experiment [122] gave a value of G0k = 3, for incident proton energies larger than 1 GeV and for a uranium target. The experiment consisted of mapping out the number of fissions produced in a multiplying array surrounding a uranium target bombarded by the CERN PS proton beam. The multiplying array consisted of natural uranium bars immersed in a light-water swimming pool. The fission density within the uranium bars was obtained from the measurements, after careful corrections for the flux depression within the bars and influence of the surroundings of the detectors. The value of k was deduced from a measurement using a known 252Cf source. From the value of G0 it is possible to deduce a value of N0 = G0uEp/0.18 = 41.5 neutrons per GeV proton, to be compared with a value of 32 which can be read on figure 6.10. The ratio of neutron multiplicities for uranium and lead amount to 1.35 for the CERN experiments and 1.50 for the measurements of Hilscher et al., to be compared with the value of 1.4 corresponding to the multiplication in uranium. Another important result of the FEAT experiment was that the neutron multiplicity per GeV saturated for proton energies above 0.8 GeV. This behaviour is illustrated in figure 6.15. For lead and 1 GeV protons, the value of G0 should be between 2.5 and 1.8 according to the value retained for the neutron multiplicity. The value of G0 = 2 was retained by the CERN group for its calculations of the energy amplifier [76].