A twin Frisch-grid ionization chamber as a selective detector for the delayed gamma-spectroscopy of fission fragments

We present a twin Frisch-grid ionization chamber. The detector is meant to provide high selective power for the study of delayed gamma-ray spectroscopy of fission fragments produced via ²⁵²Cf spontaneous fission. A mean energy resolution on the kinetic energy of fission fragments of 675 keV (FWHM) is achieved and allows us to resolve masses of fragments for fission events where neutron emission is not energetically possible. The mean mass resolution measured for these particular events amounts to 0.54 mass units (FWHM). For fission events with neutron emission a resolution of 4 mass units (FWHM) is reported. Information on fragment emission angle is measured with a resolution of 0.1 on the difference of the cosines determined for both halves of the detector. A charge resolution of 4.5 charge units (FWHM) is also demonstrated.