Investigation of the N/Z of the heavy fragmentation products – the isospin thermometer method

1. Investigation of the N/Z of the heavy fragmentation products – the isospin thermometer method D. Henzlovaa, M. V. Ricciardia, J. Benlliureb, A. S. Botvinaa, T. Enqvista, A. Kelića, P. Napolitania, J. Pereirab, K.-H. Schmidta aGSI-Darmstadt, Germany bUniv. Santiago de Compostela, Spain

2. Motivation • investigation of the properties of the nuclear matter under extreme conditions (E*, density, isospin…) understanding the supernovae explosions, formation and stability of neutron stars… • onset of rapid disintegration of nucleus observed for high E* nuclear caloric curve liquid-gas phase transition in NM • measurements of temperature information from IMFs and light fragments only Tfreeze-out from these methods ~ 5MeV J. Pochodzalla et al.,Phys. Rev. Lett. 75 (1995) 1040 • extension of the thermometry towards the heavy fragments

3. Important issues • disturbing effect of evaporation • full isotopic identification the FRagment Separator (FRS) evaporation residue corridor 208Pb+d 1AGeV properties of nuclei after long evaporation largely universal

4. Systematic investigation of <N>/Z of heavy fragmentation products fission excluded! T.Enqvist, et al.; Nuc. Phys. A658 (1999) 47 T.Enqvist, et al.; Nuc. Phys. A703 (2002) 435 M.V.Ricciradi, et al.; proc. of XXXI Hirschegg Workshop, Jan. 2003 • final fragments keep higher <N>/Z than the EPAX prediction lack of excitation energy at the beginning of evaporation • final fragments scale with the N/Z of the projectile long evaporation process keeps a memory on the initial N/Z of the system

5. Interpretation of the data • two stage process: abrasion evaporation excited prefragment • E* deposited in the prefragment by far exceeds the E* corresponding to T~5MeV ABRABLA calculation 238U+Pb 1 AGeV • possible scenario: evaporation abrasion break-up

6. Understanding the observed features - the isospin thermometer method • the isospin thermometer method explores the reduction of N/Z in evaporation process to restore the E* after break-up access to the fragment temperature at the freeze-out of the break-up stage break-up abrasion 238U upper limit of Tfreeze-out ~ 5.5 MeV evaporation 136Xe Preliminary

7. Summary • FRS allows to extend the full isotopic identification up to the mass of the projectile • FRS data for neutron rich projectiles final fragments after evaporation still keep an important information about the reaction mechanism • high E* introduced and observed deviation of the heavy fragmentation residues from the EPAX prediction signals a break-up process in their formation evaporation process = ‘tool’ to access the freeze-out of the break-up stage freeze-out temperature deduced from heavy residues in accord with IMFs investigations