[en] The technique of experimental investigation of time evolution of neutron spectra in medium in the nanosecond region during a short neutron pulse, using a californium chamber as a statistic pulse neutron source and a multichannel analyzer in the regime of multiple analysis, is considered. The results of investigation of nonstationary neutron spectra of leakage from the surface of the molybdenum sphere in the neutron energy range from 10.5 to 0.4 MeV and within the time interval from 0 to 130 ns are given. Experimental results are given in comparison with the calculation by the kinetic ROZ-V-1 program using group neutron BNAB constants. Considerable difference between calculated and experimental results is observed in the neutron energy range from 2.5 to 0.4 MeV. The difference observed is supposed to be connected with doubtfullness of neutron inelastic scattering constants for molybdenum in the used library