An experimental setup for studying spectra of β particles emitted by mixtures of 235 U and 239 Pu thermal neutron fission products

An experimental setup on the thermal neutron beam of the IR-8 reactor at the National Research Centre Kurchatov Institute is described. This setup has been designed to precisely measure the ratio of spectra of β particles emitted by mixtures of 235 U and 239 Pu fission products. The experiment is based on simultaneous measurements of β spectra from fissile isotopes 235 U and 239 Pu and the background spectrum in the same neutron beam. Measurements of the β spectra are taken by a high-selectivity β spectrometer in the time interval when the neutron beam is intercepted by a mechanical chopper. The evolution of the measurement technique is considered.