PROMPT NEUTRON-SPECTRUM MEASUREMENT OF U-238 FISSION INDUCED BY 10.17AND 12.12 MEV NEUTRONS

The prompt neutron spectra of U-238 fission induced by 10.17 and 12.12 MeV neutrons have been measured using a multi-segment fission chamber and two ST-451 liquid scintillator neutron detectors in conjunction w ith a double-TOF technique. Use of coincidence between the fission fra gments and neutrons enabled the fission neutrons to be distinguished f rom other secondary ones. The detection efficiencies of the ST-451 liq uid scintillators were determined by combining Monte Carlo calculation using a standard code NEFF4 [1] with experimental calibration using a low-mass Cf-252 ionization chamber. The measured spectra can be rough ly described by Maxwellian distributions. The Maxwellian temperatures are obtained by fitting equal 1.40+/-0.04 MeV for 10.17 MeV incident a nd 1.47+/-0.04 MeV for 12.12 MeV, respectively. The experimental spect ra are compared with theoretical calculated ones by code FINESSE [2] a nd the evaluation by ENDF/B-VI [3].