Isotopic fission-fragment distributions of U238, Np239, Pu240

Abstract

Transfer-and fusion-induced fission in inverse kinematics has proved to be a powerful tool to investigate nuclear fission, widening information on the fission fragments and access to unstable fissioning systems with respect to other experimental approaches. An experimental campaign is being carried out at GANIL with this technique since 2008. In these experiments, a beam of 238 U, accelerated to 6.1 MeV/u, impinges on a 12 C target. Fissioning systems from U to Cf are populated through inelastic scattering, transfer, and fusion reactions, with excitation energies that range from a few MeV up to 46 MeV. The use of inverse kinematics, the SPIDER telescope, and the VAMOS spectrometer allow the characterization of the fissioning system in terms of mass, nuclear charge, and excitation energy, and the isotopic identification of the full fragment distribution. This work reports on new data from the second experiment of the campaign on fission-fragment yields of the heavy actinides 238 U, 239 Np, 240 Pu, 244 Cm, and 250 Cf, which are of interest from both fundamental and application points of view.

First Direct Measurement of Isotopic Fission-Fragment Yields of U239

“…The Brownian shapemotion model with random walks on 5D potential-energy surfaces [42] predicts a continuous increase of the yield for Sn for heavier fissioning systems in the isotopic chain of uranium, for initial excitation energy around ∼ 1MeV above the fission barrier. Similar values are also obtained [25,26] (open circles) are compared with a model based on the Brownian shape-motion and on 5D potentialenergy surfaces [42] (dashed line) and with the GEF code (2018/1.1) [38] (solid line). Data from γ-spectroscopy measurement Ref.…”

“…Recent experimental results obtained from radiative neutron-capture processes and from surrogate reactions showed a strong enhancement of the γemission probability induced by the surrogate reaction with respect to the direct reaction [43], which was attributed to a larger angular momentum populated in the former reaction. However, this behavior was not observed in fission, where neutron-induced and transfer-induced fission show similar probabilities [20] and fission-fragment distributions [26]. Small variations due to angular momentum were also predicted by theoretical models.…”

“…The use of inverse kinematics allowed the direct measurement of the atomic number of complete fission-fragment distributions [22]. In the last decade, the simultaneous use of surrogate reactions, inverse kinematics, and magnetic spectrometers has opened a new field of study measuring complete isotopic fission-fragment distributions [23][24][25][26], and leading to an improved understanding of the fission process [12].…”

“…This was isotopically subtracted following the procedure described in Ref. [26]. This analysis procedure ensures that the contribution of other fissioning systems is lower than 0.9%.…”

Insight into excitation energy and structure effects in fission from isotopic information in fission yields

“…Details about the experimental setup and analysis can be found in Ref. [37]. With this technique, the simultaneous measurement of proton and neutron content of post-neutron evaporation fission fragments is achieved.…”