The thermal-neutron-induced alpha-accompanied fission of235U investigation of the low energy part of the alpha spectrum

Abstract

The energy spectrum of the α-particles emitted in the thermal-neutron induced fission of235U was measured from 11.5 MeV down to 2 MeV using the parabola mass spectrometer Lohengrin at the I.L.L. high flux reactor. This low energy part of the energy spectrum presents a smooth connection with the energy spectra which have been recently reported above 7 MeV. The overall energy spectrum, which is known to be quasi-gaussian above 12 MeV, is slightly asymmetric at low energy, where the observed particles are 6% more than expected from a gaussian shape. As a consequence, all the values reported for235U for the rate of α-accompanied fission compared to binary fission have to be multiplied by 1.06. This asymmetry is about 2 times less important than the one reported for252Cf. No evidence was seen for any intense low energy component as reported before. The possible reasons for the existence of this asymmetry are discussed.