Many Body Nuclear Dynamics Group: Research Highlights

 

Physics Results

Recent Experiments

Neutron stars -- Experimental investigation of the sub-barrier fusion of neutron-rich light nuclei is important in understanding the crusts of neutron stars, the structure of neutron-rich nuclei, and fusion dynamics of neutron-rich nuclei.  


July 2010, GANIL
 

" Near and sub-barrier fusion of neutron-rich light-ions for 20O + 12C at E/A ≤ 3 MeV"

 

Collision Dynamics -- From the backward peaked angular distributions of excited projectile-like fragment aligned breakup, a short lifetime for the rotating, deformed PLF is deduced . It is noteworthy that this short-lived dynamical yield is not restricted to fragments with ZL ≤ 10, previously thought of as "neck-fragments", but persists for fragments as large as ZL = 18 -- i.e. near symmetric splits of the PLF. The short lifetime (<1.5 x 10-21 s) of these more symmetric splits follows a smooth systematic trend from more asymmetric splits indicating that even production of these large fragments is impacted by the collision dynamics.  


June/July - October 2007, GANIL
 

" Binary breakup of excited projectile-like fragments produced in collisons of 124,136Xe nuclei with 112,124Sn targets at E/A = 50 MeV"

 

Isospin Transport -- A neutron enrichment of midrapidity nuclear material at the expense of the quasi-projectile is observed for symetric collisions when accounting for clusters and free nucleons. A likely origin for the preferential transfer of neutrons toward midrapidity is a density dependence of the symmetry energy.  


November/December 2003, TAMU
 

"Neutron transport in symmetric Heavy-Ion reaction 64Zn + 64Zn at E/A = 45 MeV "

 

Time Scales -- The time scales for multifragmentation in light-ion-induced reactions has been shown to be ≈ 20-50 fm/c, as deduced from small-angle IMF-IMF velocity correlations.  

November 1998, Argonne National Laboratory

"Spectroscopy of Proton-Decay Links from Superdeformed Minima in Mass 60 Nuclei of 36Ar + 28Si at 141 MeV"

 

Pre-Fragmentation IMF Emission -- Large-angle IMF-IMF energy correlations show that prior to multifragmentation of the hot residues, some cooling occurs via the emission of light IMFs (Li, Be. B). This result supports a time-dependent scenario for multifragmentation in which fragment emission occurs during expansion, followed by multibody breakup of the residue. October/November 1998 NSCL-MSU

"Temperature, Impact Parameter and Isospin Dependence of Neck Fragmentation of 112,124Sn + 112,124Sn at E/A = 50 MeV"

Source Properties -- One of the remarkable features of hadron-induced reactions is the deposition of energies up to ≈ 1.5 GeV in the residual nucleus while imparting little velocity, á vsource ñ ≈ 0.01 c. A rapidity analysis also indicates thermal-like behavior for the disintegrating source. These observations argue for the excitation of baryonic resonances (Δ, N*, etc.) And subsequent π reabsorption as a significant complement to N-N scattering in the energy deposition process. October/November 1998 NSCL-MSU

"Isospin Equilibration and Fragment Emission Order in the Reactions 106,114Cd + 98,92Mo at E/A = 50 MeV"

Collision Dynamics -- Multiplicity distributions for thermal-like LCPs and IMFs indicate that the average energy deposited in heavy target nuclei saturates in the vicinity of 5 GeV bombarding energy. This is explained in terms of a tradeoff between the increased projectile energy and increased transparency for fast cascade hadrons. In addition, π- and p beams are found to yield identical multiplicity results, stressing the independence of hadron type in initiating the sequence of collisions that deposits energy in the residual heavy nucleus. October 1998 NSCL-MSU

"Probing the 'Freeze-out' Mechanism for Multifragmentation Processes of 129Xe + Au at E/A = 50 MeV"

Heating Curve for Finite Nuclei -- The excitation energy vs. temperature dependence has been determined for the 4.8 GeV 3He + natAg, 197Au systems. Excitation energy distributions for the fragmenting nuclei were reconstructed event-by-event from the spectra, and temperatures were based on the double-isotope ratio method (2,3H/3,4He). The heating curve does not show a plateau, but instead a systematic increase approximately consistent with predictions of both the expanding, emitting source model (EES) model of W.A. Friedman and the statistical multifragmentation (SMM) model of A. Botvina. September 1998 NSCL-MSU

"Decay Characteristics of Thermally Induced Multifragmen- tation of 12C, 36Ar + Au at E/A = 150 MeV"

 

Nuclear Expansion -- Analysis of IMF spectra and multiplicity distributions as a function of collision violence provides strong evidence for multifragmentation from an expanded/dilute source. The breakup density appears to be less than one-third normal nuclear matter density, ρ≤ρ0/3. Direct experimental evidence for expansion/dilution comes from the Coulomb-like peaks of the IMF spectra, which are strongly distorted toward low energies for the most violent events. In addition, the expanding, emitting source model of W.A. Friedman describes both the spectra and multiplicity distributions with an effective compressibility parameter K = 144 MeV, consistent with ρ ∼ ρ0/3.
 June 1998, TAMU

"5He and Other Unstable Particle Emission from Residue Producing Reactions of Ni + Mo at E/A = 11 MeV"