Fission in Inverse Kinematics: A new window to experimental observables

by Prof. Fresco Manuel Caamaño (University of Santiago de Compostela)

LAE meeting room (INFN-LNL)

LAE meeting room


Experimentally, the understanding of the complex and intricate process of nuclear fission is approached by collecting as many observables as possible and from all fissioning systems available. The measured properties of the fissioning system and of the fission products, and their correlations, has led to the current picture where, in a very simplified way, the fission proceeds according certain modes or channels centred around fragments with particular numbers of protons and/or neutrons, which emerge with specific deformations that also drive the sharing of part of the available energy.
    Most of the information on fission was gathered so far in experiments that use direct kinematics, where the fissioning system can be considered at rest in the laboratory. However, these experiments suffer from two main drawbacks: few observables are measured simultaneously and the fragment atomic number is either absent or poor in resolution. The use of inverse kinematics, where the fissioning system is studied in-flight, opens a possibility to solve those issues and to add new information. In particular, we will discuss the use of magnetic spectrometers in order to provide the simultaneous measurement of the mass and atomic number of the fragments, as well as their velocities, which grants the access to the fissioning system reference frame.
    The correlation of the measured observables permits to recover properties such as the total kinetic energy or the neutron multiplicity that can be studied and compared with previous measurements. In addition, the measurement of the atomic number allows us to retrieve quantities such as the neutron-to-proton ratio of the fragments, the total excitation energy, and the elongation of the system can be calculated. From there, a few reasonable assumptions are enough to extract the intrinsic and collective excitation energy of the fragments as a function of their atomic number, along with their quadrupole deformation and their distance at scission.
    The discussion will mainly focus on the study of transfer- and fusion-induced fission of several systems, produced in inverse kinematics at GANIL (France). We will address the latest results on 240Pu and 250Cf, the ongoing analysis of the dependence with the fission energy, as well as future applications to the study of high-energy fission and quasi-fission.
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