Distribution of photoneutrons from pulse radiation sources measured by means of a multisphere spectrometer

Using a multisphere spectrometer, the spectra of neutrons and photoneutrons are measured in the 6-20 MeV energy range of a high-current betatron. Spherical moderators with 51, 76, 127, 203 and 305 mm radii of spheres are used. Inside each sphere a thermal neutron detector, consisting of a FEhU-31 photomultiplier and a ZnS(Ag)10B scintillator, is located. Neutrons are generated in Be, Pb, Cu and W targets. The measurements have shown that the counting rate of thermal neutrons in every counter is exponentially falling off in time. The analysis of the errors based on the measurement results has shown that according to the available statistics the error of spectrum reconstruction by means of the multisphere spectrometer is 30-35%