Ratio of the ternary to binary fission cross sections induced by resonance neutrons in ²³⁵U

Precise measurements were performed of the ratio of ternary to binary fission T B for ²³⁵U in the neutron energy region below 40 eV [by ternary fission is meant fission into two heavy fragments and one light charged particle, usually a long-range α-particle (LRA)]. The neutron energy selection was made at a 8 m flight path of the Geel Linac (Belgium). Large gold-silicon surface-barrier detectors on both sides of a 2mg/cm² back-to-back ²³⁵U target were used for the consecutive measurements of the LRA and fission fragments. Checks were made on the ternary α-particle pulse height with a neutron beam from the BR2 reactor. From the well-resolved time-of-flight versus neutron energy spectra recorded in both conditions, the ratios of the areas of the strongest isolated resonances were calculated. The T B values vary from resonance to resonance and can be classified into a "low" and a "high" group. Moreover there is a correlation between T B, the resonance spins J and some other fission characteristics.