Production of neutron-rich isotopes in fission of uranium induced by neutrons of 20 MeV average energy

In the context of a parameter study conducted by several laboratories for f uture European radioactive beam facilities based on fast-neutron induced fi ssion, in particular for the SPIRAL-II project at GANIL. we have measured t he yields of neutron-rich isotopes in the mass range of 88 to 144. These nu clei were obtained as fission products of natural uranium bombarded by neut rons of 20 MeV average energy emitted by a thick carbon target irradiated b y 50 MeV deuterons. Yields have been measured using on-line mass separation with the ion-guide method. Compared with proton-induced fission at 25 MeV the magnitude of cross-sections, except for the symmetric region, is simila r. Z-distributions of isobars have the same width: 0.7 charge units, but th eir maxima are shifted by about 0.8 charge units, favouring production of t he neutron-richer isobars. Our data allow calculations of absolute cross-se ctions for fission of natural uranium induced by neutrons of about 20 MeV.