Prompt aligned binary, ternary, and quaternary fragmentation in 48Ca + 112Sn and 48Ca + 124Sn reactions at a bombarding energy of 45 MeV/A and Radioluminescent characterization of the novel EJ 299-33 plastic scintillator for γ-rays, neutrons, and charged particles

Thesis (Ph. D.)--University of Rochester. Department of Physics and Astronomy, 2016.In the first, scientific part of this thesis, charged particle products of nuclear reactions 48Ca + 112Sn and 48Ca + 124Sn were measured at a bombarding energy of 45 A MeV using the 4π CHIMERA multi-detector array at the LNS Catania/Italy. The CHIMERA multi-detector array is capable of detecting most of the fragments produced in 48Ca + 112Sn and 48Ca + 124Sn reactions and captures the characteristics of individual charged products. In the current experiment, intermediate mass fragments (IMF) emitted from the decay of neck-like structures that temporarily join the projectile-like fragment (PLF) and target-like fragment (TLF) have been observed for mid-peripheral 48Ca + 112Sn and 48Ca + 124Sn collisions. This conclusion is deduced from analyzing the characteristics of individual reaction products and the kinematic relationships between reaction products. For events in which an IMF (3≤ZIMF≤7) is detected in coincidence with a heavy PLF remnant (ZH≥9), kinematic properties such as velocity spectra, invariant velocity distributions, relative velocities, and angular distributions are reconstructed. Reconstructed velocity spectra and invariant velocity distributions show that these IMFs occupy velocities intermediate between those of the TLF and PLF. Further analysis shows that the measured ZIMF-ZH fragment relative velocities are larger than those given by Coulomb repulsion, and have an angular distribution that is forward-backward asymmetric with the heavy PLF remnant preferentially emitted forward along the primary PLF direction and light IMF preferentially emitted backward of the primary PLF direction. These conclusions are consistent with those previously observed in other heavy-ion reactions in the Fermi energy regime. In addition, a novel class of events, in which two or more IMFs are detected in coincidence with a heavy PLF remnant, has been observed. These IMFs have velocities intermediate between those of the TLF and PLF, relative velocities larger than those expected from a purely Coulomb-driven separation. They have angular distribution that are anisotropic in the primary PLF rest frame, with the heavy PLF remnant preferentially emitted forward along the primary PLF direction and the light IMFs preferentially emitted backward of the primary PLF direction. Furthermore, the opening angle between the two IMFs velocity vectors is approximately zero, suggesting a four body exit channel with the four bodies all aligned along TLF-PLF separation axis, here termed “aligned quaternary fragmentation (AQF)”. Additional calculations show that these IMFs could not have originated from the subsequent statistical decay of an excited cluster such as 12C* formed transiently during the projectile-target interaction, but rather appear to come from the snapping of the neck-like structures into several IMFs. In a second, technical part of this work, the response of the EJ 299-33 plastic scintillator to energetic charged nuclear particles ranging from isotopes of hydrogen to isotopes of carbon has been determined over a wide energy range using a complex experimental setup and nuclear reactions induced by a 20 A MeV carbon beam on an aluminum target. A strong pulse-shape dependence of the generated light bursts on the impinging particle specie is observed, which makes this scintillator suitable, among other things, for neutron vs. γ-ray identification. Fit formulas are proposed for the normalized light output as a function of particle energy for eleven isotopes of elements ranging from hydrogen to carbon. The response of the EJ 299-33 plastic scintillator to energetic charged nuclear particles has also been analyzed in terms of Birks' semi-empirical approach over the wide range of particle energies from 2 to 20 A MeV. It was found that, while the original two-parameter scaling involving Birks' composite quenching parameter (kB) and an overall conversion efficiency parameter (S) may be applicable to select sets of particles, a more universal fit would still require adoption of individual scintillation efficiencies (Sx) for individual particle species, as well as more than just one universal value of Birks' constant kB