120610624
Sensitivity of Small-Angle Correlations of Light Charged Particles to Reaction Mechanisms in the 16O+27A1 Reaction at 40MeV/Nucleon
Small-angle $p$-$p$, $p$-$d$, $d$-$\ensuremath{\alpha}$, and $\ensuremath{\alpha}$-$\ensuremath{\alpha}$ correlation functions were measured following the reaction ${}^{16}$O+${}^{27}$Al at 40 MeV/nucleon ${}^{16}$O. These light charged particles (LCP's) were measured with a closely packed hexagonal array of CsI detectors, located at $35\ifmmode^\circ\else\textdegree\fi{}$, with a center to center opening angle of 2.35$\ifmmode^\circ\else\textdegree\fi{}$ for adjacent detectors. Coincident particles were simultaneously detected in the NSCL $4\ensuremath{\pi}$ detector. This measurement was intended to be a complement to earlier results from the same system. Based on studies of this system at lower energies and other published correlation measurements, it was expected that at 40 MeV/nucleon there would be significant positive correlations from the nuclear force and deep anticorrelations from Coulomb repulsion. However, correlation functions from this higher energy are remarkably similar to those previously measured at $\ensuremath{\approx}$15 MeV/nucleon. Correlation functions formed from events with a high multiplicity or high total detected energy (central collisions) are not significantly different from the inclusive measurements. As a possible explanation we suggest that significant correlations are most readily seen in experiments sensitive to LCP's from fast preequilibrium processes and that measurements at more backward angles are primarily sensitive to LCP's from a longer-lived source formed after preequilibrium processes are done. This idea is supported by trends of $p$-$p$ correlation functions from a wide range of systems. A schematic calculation based on a Boltzmann-Ueling-Uhlenbeck (BUU) model and statistical emission qualitatively reproduces the results from this work.
6617567
Impact parameter dependence of the disappearance of transverse flow in nuclear collisions.
19432282
The fragment coalescence model.
The extraction of source radii from heavy-ion collisions using coalescence models is explored. A new prescription is presented which considers nucleosynthesis via the coalescence of fragments which is, in particular, more appropriate for intermediate-energy collisions than the previous nucleon coalescence prescriptions. This fragment coalescence model provides an avenue for viewing the breakup stage of heavy-ion reactions that yields valuable complimentary information to two-nucleon and two-fragment correlation measurements. This model was applied to recent experimental data on central 55 and 115 MeV/nucleon {sup 40}Ar+{sup 45}Sc collisions studied at midrapidity. Source radii are presented versus the transverse velocity for six different coalescence channels leading to charge one, two, and three fragments. Particular attention is paid to the temperature input in the model, as the extracted radii depend significantly on this parameter. A means of extracting the temperature from experimental data using the present model is described. Comparisons to the two temperature-dependent nucleon coalescence models will also be discussed.
26370328
Mass dependence of the disappearance of flow in nuclear collisions.
The disappearance of collective flow in nucleus-nucleus collisions occurs at an incident energy ([ital E][sub bal]) where the attractive scattering dominant at low energies balances the repulsive scattering dominant at high energies. We have performed the first systematic study of the entrance-channel mass dependence of the disappearance of flow and hence [ital E][sub bal]. The new data presented for the C+C, Ne+Al, Ar+Sc, and Kr+Nb systems show that [ital E][sub bal] scales as [ital A][sup [minus]1/3] where [ital A] is the mass of the combined system. Boltzmann-Uehling-Uehlenbeck model calculations show trends which are in qualitative agreement with these new results.
37856497
Autocorrelations and intermediate-mass-fragment multiplicities in central heavy-ion collisions.
The average multiplicities of intermediate mass fragments (IMFs) for central heavy-ion collisions in the (nearly) symmetric entrance channels [sup 20]Ne+[sup 27]Al, [sup 40]Ar+[sup 45]Sc, [sup 84]Kr+[sup 93]Nb, and [sup 129]Xe+[sup 139]La, are systematically studied over a wide range of intermediate beam energies. Cuts on experimental variables commonly assumed to be correlated with the impact parameter are used to select the most central collisions. The results for six different centrality variables are compared, and the extent to which measurements of the multiplicities of IMFs in small impact parameter collisions are affected by the variable used to select the central events is discussed. General methods for locating such autocorrelations'' are described. The two centrality observables that are the least autocorrelated with the number of intermediate mass fragments are identified, and these variables are used to select the most central collisions. The entrance channel mass and beam energy dependence of the experimental IMF multiplicities are presented and compared to a variety of model predictions. The models picturing the disassembly as a sequential binary process always underpredict the experimental IMF multiplicities. A generally more accurate reproduction of these multiplicities is provided by several similar chemical equilibrium models commonly assumed to be the theoretical descriptionmore » of multifragmentation.« less
43759133
Multifragment azimuthal correlation functions: Probes for reaction dynamics in collisions of intermediate energy heavy ions.
Multifragment azimuthal correlation functions have been measured as a function of beam energy and impact parameter for the Ar+Sc system ([ital E]/[ital A]=35 to 115 MeV). The observed azimuthal correlation functions---which do not require corrections for dispersion of the reaction plane---exhibit strong asymmetries which are dependent on impact parameter and beam energy. Rotational collective motion and flow seem to dominate the correlation functions at low beam energies. It is proposed that multifragment azimuthal correlation functions can provide a useful probe for intermediate energy heavy ion reaction dynamics.
120988952
BRANCH WAVE FUNCTIONS FOR QUASI-CLASSICAL HOMOGENEOUS UNIVERSES
182462112
Deadtime of SDC Straw Detectors