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Abstract. The leakage neutron spectra measurements have been done on benchmark spherical assembly -iron sphere with diameter of 100 cm. The Cf-252 neutron sources with different emissions were placed into the centre of iron sphere. The proton recoil method was used for neutron spectra measurement using stilbene crystals and hydrogen proportional counters. The neutron energy range of spectrometer was from 0.01 to 17 MeV. The gamma pulse shape discrimination (PSD) method has been applied in stilbene measurements. The adequate MCNP neutron spectra calculations based on different data libraries (ENDF/B-VI.8, BROND-3, JENDL-3.3, JEFF-3.1) have been done and compared with measurements. Some aspects of presented benchmark are discussed in details including reproducibility of measurements, influence of group structure, smoothing of spectra, energy resolution of spectrometer, methodology of calculation (1-or 3-dimensional problem, results uncertainties), methodology of experiment (neutron background measurement using shadow cone). The results of analogous measurements and calculations performed on pure iron spheres of diameters 20, 30 and 50 cm are also briefly discussed in the report.

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