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Physics Results |
Recent Experiments with LASSA |
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,  .
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  . |
June
1998, TAMU
"5He and Other Unstable Particle Emission from Residue Producing Reactions of Ni + Mo at E/A = 11 MeV"
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| 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"
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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,  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" |
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, <vsource>
0.01 c. A rapidity analysis also indicates thermal-like behavior for the
disintegrating source. These observations argue for the excitation of
baryonic resonances ( ,
N*, etc.) And subsequent 
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" |
| 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" |
| 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"
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"N/P Invariant Cross Sections Maps and PLF Velocity Measurements of Xe + Sn,Au at E/A = 40 MeV"
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