H. Orth

Isotopic dependence of the nuclear caloric curve

The A/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at SIS. A stable beam of (124)Sn and radioactive beams of (124)La and (107)Sn at 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. Chemical freeze-out temperatures are found to be nearly invariant with respect to the A/Z of the produced spectator sources, consistent with predictions for expanded systems. Small Coulomb effects (DeltaT approximately 0.6 MeV) appear for residue production near the onset of multifragmentation.

N/Z DEPENDENCE OF PROJECTILE FRAGMENTATION

The N/Z dependence of projectile fragmentation at relativistic energies has been studied in a recent experiment at the GSI laboratory with the ALADiN forward spectrometer coupled to the LAND neutron detector. Besides a primary beam of 124Sn, also secondary beams of 124La and 107Sn delivered by the FRS fragment separator have been used in order to extend the range of isotopic compositions of the produced spectator sources. With the achieved mass resolution of ΔA/A ≈ 1.5%, lighter isotopes with atomic numbers Z ≤ 10 are individually resolved. The presently ongoing analyses of the measured isotope yields focus on isoscaling and its relation to the properties of hot fragments at freeze-out and on the derivation of chemical freeze-out temperatures which are found to be independent of the isotopic composition of the studied systems. The latter result is at variance with the predictions for limiting temperatures as obtained with finite-temperature Hartree-Fock calculations.

Mass and Isospin Effects in Multifragmentation

A systematic study of isospin effects in the breakup of projectile spectators at relativistic energies has been performed with the ALADiN spectrometer at the GSI laboratory (Darmstadt). Four different projectiles 197Au, 124La, 124Sn and 107Sn, all with an incident energy of 600 AMeV, have been used, thus allowing a study of various combinations of masses and N/Z ratios in the entrance channel. The measurement of the momentum vector and of the charge of all projectile fragments with Z>1 entering the acceptance of the ALADiN magnet has been performed with the high efficiency and resolution achieved with the TP-MUSIC IV detector. The Rise and Fall behavior of the mean multiplicity of IMFs as a function of Zbound and its dependence on the isotopic composition has been determined for the studied systems. Other observables investigated so far include mean N/Z values of the emitted light fragments and neutron multiplicities. Qualitative agreement has been obtained between the observed gross properties and the predictions of the Statistical Multifragmentation Model.

Discriminant analysis and secondary-beam charge recognition

The discriminant-analysis method has been applied to optimize the exotic-beam charge recognition in a projectile fragmentation experiment. The experiment was carried out at the GSI using the fragment separator (FRS) to produce and select the relativistic secondary beams, and the ALADIN setup to measure their fragmentation products following collisions with Sn target nuclei. The beams of neutron poor isotopes around La-124 and Sn-107 were selected to study the isospin dependence of the limiting temperature of heavy nuclei by comparing with results for stable Sn-124 projectiles. A dedicated detector to measure the projectile charge upstream of the reaction target was not used, and alternative methods had to be developed. The presented method, based on the multivariate discriminant analysis, allowed to increase the efficacy of charge recognition up to about 90%, which was about 20% more than achieved with the simple scalar methods.

Neutron recognition in the LAND detector for large neutron multiplicity

The performance of the LAND neutron detector is studied. Using an event-mixing technique based on one-neutron data obtained in the S107 experiment at the GSI laboratory, we test the efficiency of various analytic tools used to determine the multiplicity and kinematic properties of detected neutrons. A new algorithm developed recently for recognizing neutron showers from spectator decays in the ALADIN experiment S254 is described in detail. Its performance is assessed in comparison with other methods. The properties of the observed neutron events are used to estimate the detection efficiency of LAND in this experiment

Gross Properties and Isotopic Phenomena in Spectator Fragmentation

A systematic study of isotopic effects in the break-up of projectile spectators at relativistic energies has been performed with the ALADiN spectrometer at the GSI laboratory. Searching for signals of criticality in the fragment production we have applied the model-independent universal fluctuations theory already proposed to track criticality signals in multifragmentation to our data. The fluctuation of the largest fragment charge and of the asymmetry of the two and three largest fragments and their bimodal distribution have also been analysed.

Isotopic dependence of the caloric curve

Isotopic effects in projectile fragmentation at relativistic energies have been studied with the ALADIN forward spectrometer at SIS. Stable and radioactive Sn and La beams with an incident energy of 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. Chemical freeze-out temperatures are found to be nearly invariant with respect to the A/Z ratio of the produced spectator sources, consistent with predictions for expanded systems. Consequences for the proposed interpretation of chemical breakup temperatures as representing the limiting temperatures predicted by microscopic models are discussed.

ISOTOPIC TEMPERATURES AND SYMMETRY ENERGY IN SPECTATOR FRAGMENTATION

R. BASSINI5), , C. BOIANO5), A.S. BOTVINA2), A. BOUDARD6), J. BRZYCHCZYK4), A. CHBIHI1), J. CIBOR8), B. CZECH8), J.-E. DUCRET6), H. EMLING2), J. FRANKLAND7), M. HELLSTROM2), D. HENZLOVA1), K. KEZZAR2), G. IMME1), I. IORI5), H. JOHANSSON2), A. LAFRIAKH3), , E. LE GENTIL6), Y. LEIFELS2) , W.G. LYNCH9), J. LUHNING2), , U. LYNEN2), Z. MAJKA4), M. MOCKO9), W.F.J. MULLER2), A. MYKULYAK10), H. ORTH2), A.N. OTTE2), R. PALIT2), P. PAW LOWSKI8) , A. PULLIA5), G. RACITI1), E. RAPISARDA1), H. SANN2), C. SCHWARZ2), H. SIMON2), K. SUMMERER2), M.B. TSANG9), C. VOLANT6), M. WALLACE9), H. WEICK2), J. WIECHULA2), A. WIELOCH4) and B. ZWIEGLINSKI10) 1) Dipartimento di Fisica, Universita degli studi di Catania and LNS-INFN, 64, Via S. Sofia, I-95123 Catania, Italy 2) Gesellschaft fur Schwerionenforchung, D-64291 Darmstadt, Germany 3) Institut de Physique Nucleaire, IN2P3-CNRS et Universite, F-91406 Orsay, France 4) M. Smoluchowski Institute of Physics, Jagiellonian Univ., Pl-30059 Krakow, Poland 5) Istituto di Scienze Fisiche, Universita degli Studi and INFN, I-20133 Milano, Italy 6) DAPNIA/SPhN, CEA/Saclay, F-91191 Gif-sur-Yvette, France 7) GANIL, CEA et IN2P3-CNRS, F-14076 Caen, France; 8) H. Niewodniczanski Institute of Nuclear Physics, Pl-31342 Krakow,Poland 9) Department of Physics and Astronomy and NSCL, MSU, East Lansing, MI 48824, USA; 10) A. So ltan Institute for Nuclear Studies, Pl-00681 Warsaw, Poland