This paper reviews the experimental and theoretical studies of breakup processes induced by He projectiles. For this type of reaction knowledge of three-body kinematics is imperative; hence important aspects are summarized. Although some nuclear structure information has been studied with this type of reaction, the emphasis of this review is mainly on the reaction mechanism. The phenomena described here are quite general, so the consequences for other projectiles (i.e., heavy ions) are also discussed.
The mean multiplicity of intermediate mass fragments (IMF) (M«") produced by fragmentation of Au projectiles interacting with targets of C, Al, Cu, and Pb at an incident energy of E/A =600 MeV is compared to predictions of statistical multifragmentation and sequential evaporation models. The initial conditions for the calculations were provided by Boltzmann-Uehling-Uhlenbeck simulations. In the high excitation energy regime where the IMF multiplicity reaches its maximum the observed universal correlation between (M«") and the total charge Zb, ""~o f projectile fragments with charges Z~2 cannot be reproduced by a sequential evaporation code. In this regime the data are better described by statistical decay calculations which assume the formation of an expanded nuclear system and a rather fast breakup.
We have studied the fragmentation of Au projectiles interacting with targets of C, A1 and Cu at an incident energy of E/A = 600 MeV. The employed inverse kinematics allowed a nearly complete detection of projectile fragments with charge Z > 2. The recorded fragmentation events were sorted according to three observables, the multiplicity Mtp of light charged particles, the largest atomic number Zma x within an event, and a new observable, Zbound, representing the sum of the atomic numbers Z of all fragments with Z>__ 2. Using these observables, the impact parameter dependence of the fragmentation process was investigated. For all three targets, a maximum mean multiplicity of 3 to 4 intermediate mass fragments (IMFs) is observed. The corresponding impact parameters range from central collisions for the C target to increasingly peripheral collisions for the heavier targets. It is found that the correlation between the IMF multiplicity and Zbouna, extending from evaporation type processes (large Zbouna) to the total disassembly of the projectile (small Zbound) , is independent of the target nucleus. This universal behaviour may suggest an -at least partial -equilibration of the projectile fragment prior to its decay.
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