Abstract
Recent experimental studies have shown the presence of pre-compound emission component in heavy ion reactions at low projectile energy ranging from 4 to 7 MeV/nucleons. In earlier measurements strength of the pre-compound component has been estimated from the difference in forward-backward distributions of emitted particles. Present measurement is a part of an ongoing program on the study of reaction dynamics of heavy ion interactions at low energies aimed at investigating the effect of momentum transfer in compound, precompound, complete and incomplete fusion processes in heavy ion reactions. In the present work on the basis of momentum transfer the measurement of the recoil range distributions of heavy residues has been used to decipher the components of compound and pre-compound emission processes in the fusion of 16 O projectile with 159 Tb and 169 Tm targets. The analysis of recoil range distribution measurements show two distinct linear momentum transfer components corresponding to pre-compound and compound nucleus processes are involved. In order to obtain the mean input angular momentum associated with compound and pre-compound emission processes, an online measurement of the spin distributions of the residues has been performed. The analysis of spin distribution indicate that the mean input angular momentum associated with pre-compound products is found to be relatively lower than that associated with compound nucleus process. The pre-compound components obtained from the present analysis are consistent with those obtained from the analysis of excitation functions.
Highlights
The pre-compound (PCN) emission process in heavy ion reactions at relatively low energies ranging from 4 to 7 MeV/nucleon has been a topic of recent interest [1], since it is, generally, expected to occur at relatively high energies ⇡10-15 MeV/nucleon[2]
The PCN process may be understood as the fusion of two heavy nuclei in such a way so that a composite nucleus forms far from the statistical equilibrium, and a large fraction of its energy is considered to be in the form of an orderly translational motion of the nucleons of the projectile and target nucleus[3,4,5,6,7,8]
The thermalization process completes when the composite nucleus reaches a state of thermal equilibrium referred to as compound nucleus (CN)
Summary
The pre-compound (PCN) emission process in heavy ion reactions at relatively low energies ranging from 4 to 7 MeV/nucleon has been a topic of recent interest [1], since it is, generally, expected to occur at relatively high energies ⇡10-15 MeV/nucleon[2]. The PCN process may be understood as the fusion of two heavy nuclei in such a way so that a composite nucleus forms far from the statistical equilibrium, and a large fraction of its energy is considered to be in the form of an orderly translational motion of the nucleons of the projectile and target nucleus[3,4,5,6,7,8] This orderly motion transforms slowly into chaotic thermal motion through a series of two-body interactions. The rate of emission of the PCN nucleons depends on the complexity of self-consistent mean-field interaction between the projectile and target nucleus, their structure e↵ects[7, 9] and excitation energy availed by nucleons of composite system.
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