A new detector system for the measurement of high-energy prompt γ -rays for low-energy neutron induced fission

We have developed a new setup to measure prompt fission γ -ray spectra in neutron induced fission up to energies sufficient to reveal the structure associated with giant dipole resonances of fission fragments. The setup consists of multi-wire proportional counters , to detect both fission fragments in coincidence, and two large volume (101.6 mm in diameter and 127.0 mm in length) LaBr 3 (Ce) scintillators , to measure the γ rays. The setup was used to obtain the prompt fission γ -ray spectrum for thermal neutron induced fission of 235 U at the PF1B cold-neutron beam facility of the Institut Laue-Langevin, Grenoble, France. We have successfully measured the γ -ray spectrum up to energies of about 20 MeV, what extends the currently known γ -ray spectrum limit to higher energies by approximately a factor of two.