Evidence for the role of proton shell closure in quasi-fission reactions from X-ray fluorescence of mass-identified fragments

TL;DR

This study provides experimental evidence that proton shell closure at Z=82 significantly influences quasi-fission fragment formation, using innovative simultaneous measurement of atomic numbers and masses.

Contribution

It introduces a novel experimental method for full identification of quasi-fission fragments, revealing the impact of proton shell closure on reaction outcomes.

Findings

Maximum production yield at Z=82 indicates shell closure influence.

Experimental results align with time-dependent Hartree-Fock predictions.

New approach enables detailed studies of N/Z evolution in quasi-fission.

Abstract

The atomic numbers and the masses of fragments formed in quasi-fission reactions have been simultaneously measured at scission in 48 Ti + 238 U reactions at a laboratory energy of 286 MeV. The atomic numbers were determined from measured characteristic fluorescence X-rays whereas the masses were obtained from the emission angles and times of flight of the two emerging fragments. For the first time, thanks to this full identification of the quasi-fission fragments on a broad angular range, the important role of the proton shell closure at Z = 82 is evidenced by the associated maximum production yield, a maximum predicted by time dependent Hartree-Fock calculations. This new experimental approach gives now access to precise studies of the time dependence of the N/Z (neutron over proton ratios of the fragments) evolution in quasi-fission reactions.