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Dissertation/Thesis Abstract

Non-Equilibrium Splits of the Projectile and the Mechanism of Calcium plus Tin Reactions at 45 AMeV
by Quinlan, Michael J., Ph.D., University of Rochester, 2011, 281; 3478351
Abstract (Summary)

Charged products of the medium-energy heavy-ion reaction of Ca and Sn (here studied at 45 AMeV) were measured by the 4π CHIMERA multi-detector. This multi-detector is capable of detecting the majority of fragments produced in individual Ca and Sn collisions and identifies characteristics of individual products. The characteristics are used to reconstruct the heavy-ion collision dynamics. These dynamics are of fundamental interest to studies of nuclear reactions and are important in attempts to determine the nuclear equation of state.

In the present work, the kinematic relationships between the reaction products are compared to the predictions of reaction models of varying complexity. The analysis suggests that in the collision the friction-like dissipation of the projectile's kinetic energy is less than predicted by transport models developed for low-energy heavy-ion reactions (E<10 AMeV). However, a microscopic, molecular dynamics model which should be better suited to predict the dynamics of medium-energy heavy-ion reactions also fails to reproduce key observables such as the amount of kinetic energy dissipated and the laboratory deflection angle of the projectile-like primary reaction product.

Additional analysis of the kinematic relationships has been performed. Of note is the fact that the binary division of the primary projectile-like reaction product displays an angular distribution that is not symmetric about 90° with respect to the direction of motion, suggesting that a split occurs before this product reaches equilibrium. In the rest-frame of the emitter, the angular distribution of the lighter daughter fragment is “backward” peaked. This inference is consistent with those previously reported in studies of other medium-energy heavy-ion reactions. However, a novel class of events corresponding to “forward” splits have been observed. In comparison with those previously known to exist, the forward splits are found to be produced in more central projectile-target collisions. The relative yield of these two classes of events represents a novel experimental observable which is compared to the model predictions. Despite the fact that an impact parameter dependence is observed, a model relating the split asymmetry and product yield to the geometric projectile-target overlap is unable to reproduce the observations. This suggests that the characteristics of the products formed in the split are not solely related to the geometric overlap between the projectile and target nuclei and that some amount of friction-like dissipation is required to model the heavy-ion dynamics.

Indexing (document details)
Advisor: Schroeder, W. Udo
Commitee: Farrar, James, Krauss, Todd, Manly, Steven, Thorndike, Edward
School: University of Rochester
Department: School of Arts and Sciences
School Location: United States -- New York
Source: DAI-B 73/01, Dissertation Abstracts International
Subjects: Nuclear chemistry, Nuclear physics
Keywords: Chimera multi-detector, Energy dissipation, Heavy-ion reaction, Projectile fragmentation, Reaction mechanism
Publication Number: 3478351
ISBN: 978-1-124-95795-1
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