Reaction kinematics and isospin thermometry from inclusive observables
Reaction kinematics and isospin thermometry from inclusive observables GANIL – Paolo Napolitani GSI (CHARMS) – IPN d’Orsay FRagment Separator, GSI • High-resolution achromatic mode • Inverse kinematics. • Liquid hydrogen target BE AM Measurements • Nuclide identification (TOF, trajectory, IC. ) • High-resolution velocities from Br. Research and results Target, Beam-current monitor Position TO Br F Position Br Z • Kinematics of projectile fragments [P. Napolitani et al. Phys. Rev. C 70 (2004) 054607] • Isotopic composition, isospin thermometer [K. -H. Schmidt et al. Nucl. Phys. A 710 (2002) 157] • Thermal multifragmentation induced by protons (1 A Ge. V) [P. Napolitani, Thesis]
Kinematical observable: Longitudinal velocities 15 mr angular acceptance: for light fragments only longitudinal velocities can be measured 1 A Ge. V • 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. Few-body decay Multi-body decay
Results on longitudinal velocities along a N=Z+1 chain for 136 Xe (1 A Ge. V) +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.
Nuclide production 1 A Ge. V li bi ty N /Z a st b r n atio o d i r or c r po a v e 1 A Ge. V Z • Different cross-section distributions in the two reactions reflect different distributions of E* • Crossing of b-stability • Overlap of the N /Z observable for systems related to equal N /Z of the source.
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 => 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 1 st order phase transition. • Overlap persists up to A ~ 40 => large asymmetries. Toy model • Evaporation corridor not reached: the evaporation process can be backtraced • T ~ 5 + 0. 5 Me. V -
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