A time-of-flight spectrometer for unslowed fission fragments

The one-armed time-of-flight spectrometer mounted in a vertical experimental port of the research reactor of the Moscow Engineering Physics Institute (MEPhI) was designed for measuring mass-energy distributions of unslowed fission fragments. The study of rare fission modes in the yield regions up to 10-6 is carried out having a target location near the reactor core and an electrostatic particle guide system installed, which increases the efficiency ratio of the spectrometer by a factor of 50. The special 'heavy ion generator' operation mode of the spectrometer can be used for studies of fast (≅ MeV/amu) heavy ion interaction with matter. The fission fragment energy is measured by an ionization chamber or a semiconductor detector. The negligible angular divergence of the fragment beam enables fission fragment detection in a channeling registration mode to improve the energy resolution of semiconductor detectors. The fragment velocity is determined by the time of flight between two time pick-off microchannel plate detectors. A new procedure using unseparated fission fragments was developed to obtain the correct value for the time resolution of the system. (orig.)