Reaction kinematics and isospin thermometry

1

• Reaction kinematics and isospin thermometry
• from inclusive observables
• Paolo Napolitani
• GANIL GSI (CHARMS) IPN dOrsay
• FRagment Separator, GSI
• High-resolution achromatic mode
• Inverse kinematics.
• Liquid hydrogen target
• Measurements
• Nuclide identification (TOF, trajectory, IC.)
• High-resolution velocities from Br.
• Research and results
• Kinematics of projectile fragments P.
  Napolitani et al. Phys.Rev. C70 (2004) 054607
• Isotopic composition, isospin thermometer K.-H.
  Schmidt et al. Nucl.Phys. A710 (2002) 157
• Thermal multifragmentation induced by protons (1
  A GeV) P. Napolitani, Thesis

Target, Beam-current monitor
BEAM
Position
Br
TOF
Position
Br
Z
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Kinematical observable Longitudinal velocities

• 15mr angular acceptance for light fragments only
  longitudinal velocities can be measured
• Isotopically identified fragments.
• High resolution due to Br measurement.
• Inverse kinematics no energy threshold.
  (direct kinematics only Ek tails can be
  measured, centre is missing in corresponding
  velocity spectra!)
• Experimental yields (dots) are very close to
  the evaluated invariant cross sections (lines).
• The transition from a chaotic-dominated process
  to a Coulomb- (or expansion-) dominated process
  can be observed.

1 A GeV
Multi-body decay
Few-body decay
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Results on longitudinal velocities along a NZ1
chain for 136Xe (1 A GeV) Ti,p

• Chaotic-dominated process and Coulomb- (or
  expansion-) dominated process are mixed with
  different proportions in the two systems.
• Different mean recoil for the two processes.
• Asymmetric fragmentation reflected in the
  high velocities and in the double-humped spectra
  of light fragments.

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Nuclide production

1 A GeV
1 A GeV
b-stability
?N?/Z
evaporation corridor
1 A GeV
Z

• Crossing of b-stability
• Overlap of the ?N?/Z observable for systems
  related to equal ?N?/Z of the source.

• Different cross-section distributions in the
  two reactions reflect different distributions of
  E

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Isotopic observable thermodynamic properties of
the source

• Velocity and production observables
• Nuclides issued of very different distributions
  of E in the two reactions.
• Isotopic observable
• independence of the entrance channel gt
  indication of thermal equilibrium.
• overlap reflects a constant value of T
  associated to the break-up, independent of E.
• Expected if fragmentation is associated to 1st
  order phase transition.
• Overlap persists up to A 40 gt large
  asymmetries.
• Toy model
• Evaporation corridor not reached the
  evaporation process can be backtraced
• T 5 0.5 MeV

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