Investigation of fast neutron spectra in the uranium assembly of the experimental setup “energy plus transmutation” in the JINR Nuclotron proton beam at an energy of 1.5 GeV

The “energy plus transmutation (EPT)” electro-nuclear experimental assembly (lead target surrounded with natural uranium blanket) was irradiated with protons of energy 1.5 GeV from the Nuclotron accelerator of the JINR. The energy spectrum of the neutrons in the EPT was determined by examination of 5000 proton recoil tracks in the nuclear emulsion spectrometer that was developed for these measurements. The measured energy spectrum was corrected for the laboratory background events in the emulsion. The neutron spectrum extends from 0.5 to 200 MeV. The weighted mean energy of the neutrons is in the range of 4–6 MeV depending on the energy cutoff boundaries of the spectrum. The obtained experimental results were compared with Monte Carlo calculations using the MCNPX 2.6C code and the origins of the observed discrepancies are discussed.