Speaker
Description
As demonstrated by the extensive experimental and theoretical work conducted over the past decades, nuclear fission is a highly complex process. This complexity arises primarily from the interplay of diverse aspects of both reaction dynamics and nuclear structure, which together determine the observables measurable in the laboratory. Recent studies have shown that coincidences among multiple observables are crucial to unravel the intricacies of fission and ensure an unambiguous interpretation of the data. In this context, an innovative experimental setup was developed at GANIL, coupling for the first time the VAMOS++ heavy-ion spectrometer with the new-generation PARIS scintillator array. While VAMOS++ accurately identifies the mass and charge of the fission fragments, PARIS detects with unprecedented quality the coincident gamma rays over their full dynamical range, alongside information on coincident neutrons. This contribution presents the first experiment using PARIS@VAMOS, dedicated to fission induced by fusion and nucleon transfer in 238U + 9Be collisions around the barrier. A selection of results illustrates the performance of the setup in terms of efficiency, resolution, and sensitivity, highlighting the variety of topics that can be addressed. In particular, the so-called fission gamma bump and its highly probable connection to the Pygmy Dipole Resonance are demonstrated through calculations employing microscopic nuclear level densities and gamma strength functions [1]. This connection has a dual impact: it establishes the gamma bump as a relevant signature of post-scission dynamics, and it proposes fission as a new probe of soft dipole modes, complementary to conventional approaches.
References
[1] N. Kumar, Ch. Schmitt, M. Ciemała, et al., "First experimental isotopic mapping of the fission “γ-bump” and its connection to the Pygmy dipole resonance", Phys. Lett. B 878 (2026) 140506