PISTA, a new detection system for transfer-induced fission studies in inverse kinematics at VAMOS

par Lucas Bégué-Guillou (LP2iB)

vendredi 10 juil. 2026, 11:00 → 13:00 Europe/Paris

More than 80 years after its discovery, a complete description of the fission
process remains a challenge. It is a many-body dynamic problem involving both
microscopic and macroscopic aspects of nuclear matter. New experimental data on
exotic fissioning systems that cannot be probed using direct neutron induced fission are
needed to further understand the fission process. Moreover, technological
breakthroughs such as the development of Gen-IV reactors and various fundamental
aspirations bring motivation for the scientific community to have a better
understanding of this mechanism.
At GANIL, fission studies using the VAMOS++ large acceptance spectrometer
combined with 238U beams at energies around the Coulomb barrier allow to populate
exotic fissioning systems. Also, fission induced by transfer or fusion reaction in inverse
kinematics allows obtaining isotopic identification (in mass and charge) of fission
fragments. Furthermore, the detection and identification of the target-like residue
provide the characterization of the fissioning systems in terms of mass, atomic number
and excitation energy. Such a combination has been shown to be a powerful tool to
extract post-evaporation isotopic yields and neutron content (N/Z) that hold the
signature of the shell effects at play in the process [1] as well as fission barrier [2].
Recently, an upgrade of the target-like residue detection systems has been
initiated. For this, the new PISTA (Particle Identification Silicon Telescope Array)
detector has been developed. PISTA is an array of eight trapezoidal silicon telescope
detectors assembled as in a corolla. Each telescope is composed of two single sided
silicon detectors, 100 μm and 1000 μm thick, placed 10 cm from the target. The array
covers angles between 30° and 60°. Target-like nuclei are identified using (ΔE, E)
technique up to Oxygen isotopes, resulting in the characterisation of the fissioning
system. The high angular granularity of the detector allows the reconstruction of the
reaction kinematics, thus allowing the reconstruction of the Excitation energy of the
fissioning system using two-body kinematics. Thanks to this detection system coupled
to VAMOS++, isotopic fission yields with high statistics per energy bin of about 1 MeV in
excitation energy from 6 up to 20 MeV is expected.
In this presentation, the results of the first experiment using PISTA will be
discussed. This experiment used a 238U beam at 6 A MeV impinging on a 100 μg/cm2
thick 12C target. The characteristics and the performances of the PISTA detection
system will be presented.

[1] D. Ramos et al. Phys. Rev. C 101, 034609 (2020)
[2] C. Rodríguez-Tajes et al. Phys. Rev. C 89, 024614 (2014)
[3] Rejmund, M., et al. NIM Section A 646 (2011): 184-191