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E-Verhandlungen 1998
Programm und Abstacts der Sitzung HK 52

•Boris Tomáik¹, Ulrich Heinz¹ und Ján Piút^2
1Institut für Theoretische Physik, Universität Regensburg, D-93040 Regensburg, Germany
²Faculty of Mathematics and Physics, Comenius University, Mlynská Dolina, SK-84215 Bratislava, Slovakia

Studying the Bose-Einstein correlations resulting from ``random walk models'' [1,2] we draw the conclusion [3] that they are not able to describe the data from CERN/SPS experiments. These models cannot accomodate the rise of the longitudinal correlation radius with the size of the collision system. They also fail to reproduce the magnitude and M_^-dependence of the transverse correlation radius R_s. The measured data of R_s in Pb+Pb collisions indicate a source which is in transverse direction approxinately twice as big as the original lead nucleus. This requires transverse collective expansion in those collisions.

[1] A. Leonidov, M. Nardi, H. Satz, Z. Phys. C 74, 535 (1997); Nucl. Phys. A 610 124c, (1996).

[2] S. Jeon, J. Kapusta, Phys. Rev. C 56, 468 (1997).

[3] B. Tomáik, U. Heinz, J. Piút, submitted to Phys. Lett. B, nucl-th/9711013.

* Supported by DAAD, BMBF, GSI, and DFG.

•Christiane Kuhrts, Michael Beyer und Gerd Röpke
Fachbereich Physik, Universität Rostock, 18051 Rostock, Germany

Im Rahmen einer systematischen Clusterentwicklung der quantenkinetischen Theorie zur Beschreibung von Kernmaterie treten bereits für den einfachsten Fall - die Formation von Deuteronen - Dreiteilchenstöße auf. Das Stoßintegral der verallgemeinerten Quanten-Boltzmann-Gleichung hängt dabei von der Übergangswahrscheinlichkeit für die Aufbruchreaktion Nd®NNN ab. Dies müssen in dem für Schwerionenstöße bei einer Streuenergie von E/A < 200MeV mit Faddeevmethoden behandelt werden. Dazu haben wir die AGS-Formulierung dieser Gleichungen entsprechend erweitert, um den wesentlichen Einfluß des Mediums: 1) Selbstenergiekorrekturen der Nukleonmassen und 2) Pauliblocking zu berücksichtigen [1]. Die Prozesse sind relevant z.B. für die Endphase der Schwerionenreaktion. Die Zeitskala für die Formation von Deuteronen ändert sich signifikant, wenn Mediumeffekte im elementaren Aufbruchquerschnitt berücksichtigt werden [2].

[1] M. Beyer, G. Röpke, A. Sedrakian, Phys. Lett. B 376 (1996) 7.

[1] M. Beyer, G. Röpke, Phys. Rev. C Nov. (1997).

J. Friese¹, H. Geissel², •R. Gernhäuser¹, J. Homolka¹, A. Kastenmüller¹, P. Kienle¹, H.-J. Körner¹, M. Münch¹, R. Schneider¹, A. Stolz¹, K. Sümmerer² und K. Zeitelhack^1
1Physik-Dep. E12, TU-München, D-85748 Garching
²GSI, Darmstadt

We studied projectile fragmentation of exotic secondary beams in the mass region 84 £ A £ 96 . The beams with an A/Q ratio far from stability were produced by fragmentation of ⁹⁶Zr and ⁹⁶Ru ions from the heavy ion synchrotron (SIS-GSI) with E = 1AGeV on a 4 g/cm² Be target. At the central focal plane of the fragment separator (FRS) the secondary beam ions were fully identified with respect to mass number and nuclear charge. The essential velocity information was obtained by a new kind of Ring Imaging Cherenkov detector (RICH) [1]. The instable projectiles were then directed to a second 4 g/cm² Be target. Identification of secondary fragments was performed by standard DE-TOF-Br measurement in the 2^nd half of the FRS. We report on fragmentation cross sections for selected secondary isotopes and corresponding total reaction cross sections. A comparison of the results to the INC-model "`ISAPACE"' showes good agreement in a wide range of projectile isospins -8 £ T_z £ -2.

^* supported by BMBF(06TM365) and GSI.

[1] R. Gernhäuser, et al., Nuc. Inst. Meth. A 371, 300-304 (1996 )

K. Morawetz¹, P. Lipavskyý² und V. Spi cka^2
1FB Physik, Universität Rostock, Universitätsplatz 3, D-18051 Rostock
²Institute of Physics, Academy of Sciences, Cukrovarnická 10, 16200 Praha 6, Czech Republic

A kinetic equation which combines the quasiparticle drift of Landau's equation with a dissipation governed by a nonlocal and noninstant scattering integral in the spirit of Enskog corrections is derived [1,3]. These corrections are expressed in terms of shifts in space and time that characterize non-locality of the scattering integral. The space shifts parallel finite-diameter corrections to collisions of hard spheres. The time shift is identified as the collision delay [2]. All shifts are given by derivatives of the phase shift in a binary collision [3]. Compared to the BUU- equation, the presented form of virial corrections only slightly increases the numerical demands in implementations. Consequences on current BUU- simulations are discussed and the results for heavy ion simulations are presented [3]. Consequent balance equations for the density, momentum and energy include quasiparticle contributions and the second order quantum virial corrections. The medium effects on binary collisions are shown to mediate the latent heat, i.e., an energy conversion between correlation and thermal energy [4]. This energy conversion is proposed to be of importance to understand the energy balance of recent heavy ion reaction experiments.

[1] V. Spi cka, P. Lipavský, K. Morawetz, Phys. Rev. B. 55, 5084 (1997); 5095 (1997).

[2] P. Danielewicz and S. Pratt, Phys. Rev. C 53, 249 (1996).

[3] P. Lipavský, K. Morawetz and V. pika,, Rev. Mod. Phys., (1997), sub.

[4] V. pika, P. Lipavský, and K. Morawetz, Phys. Lett. A, (1997), sub.

•T. Ritz und W. Scheid
Institut für Theoretische Physik, Universität Gießen, Heinrich-Buff-Ring 16, 35392 Gießen

Experimente zur Photoanregung zeigen, daß die Nukleonenemission aus Kernen im Energiebereich zwischen den Riesenresonanzen und der Pionenschwelle durch den (g,pn)-Prozeß dominiert wird. Dieser Prozeß kann mit kurzreichweitigen Korrelationen zwischen den Nukleonen erklärt werden. Zur Beschreibung der Anregung eines schweren Kerns durch das elektromagnetische Feld eines relativistischen Schwerions verwenden wir die Tamm-Dancoff-Näherung, wobei der Prozeß der Abspaltung eines Nukleons auch im energetisch niedriger liegenden Bereich der Dipol-Riesenresonanz untersucht wird. Die Anregung im Targetkern wird in diesem Modell durch Ein-Teilchen-Ein-Loch- Zustände in einem Oszillatorpotential beschrieben. Kurzreichweitige Korrelationen zwischen den Nukleonen werden durch die Restwechselwirkung erfaßt.

Unterstützt durch BMBF 06GI847

•F. Nuoffer¹, G. Bartnitzky¹, A. Blazevic², H.G. Bohlen², J.M. Casandjian³, M. Chartier³, H. Clement¹, B. Gebauer², A. Gillibert⁴, A. Lepine-Szily³, W. Mittig³, W. von Oertzen², A.N. Ostrowski³, P. Roussel-Chomaz³, M. Wilpert² und Th. Wilpert^2
1Physikalisches Institut der Universität Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen
²Hahn-Meitner-Institut, Glienicker Str. 100, D-14109 Berlin
³GANIL, Bd. Henri Becquerel, F-14021 Caen
⁴CEN Saclay, F-91191 Gif-sur-Yvette Cedex

The refractive part in elastic nucleus-nucleus scattering is associated with the effective nucleon-nucleon interaction at high overlap densities. This way this process simulates a situation as it is of relevance for the equation of state for cold nuclear matter. The systematics of measurements on the systems ¹⁶O + ¹⁶O and ¹⁶O + ⁴⁰Ca have been extended up to energies of 70 MeV/N by recent measurements at GANIL. The new data are discussed in connection with the systematics at lower energies and compared to calculations based on a microscopic effective interaction [1].
[1] G. Bartnitzky et al., Phys. Lett. B386 (1996) 7

^*supported by DFG (Mu 705/3, Graduiertenkolleg)

•D.V. Kamanin^1,2, C.-M. Herbach¹, H.-G. Ortlepp¹, K.D. Schilling¹, V.G. Tichtchenko², W. Wagner¹ und R. Yanez¹ für die FOBOS-Kollaboration
¹Research Center Rossendorf Inc., 01314 Dresden, Germany
²Joint Institute for Nuclear Research, 141980 Dubna, Russia

The relatively light ¹⁴N projectile has been used on heavy targets of ¹⁹⁷Au, ²³²Th to select the fission of equilibrated system after incomplete fusion. The CsI(Tl)-crystal shell of 4p-fragment spectrometer FOBOS has been used to measure the light charged particles (LCP) accompanying fission. For fission fragment (FF) pairs registrated in the gas-filled detector array, both masses and velocity vectors have been determined. The further analysis includes the mass splits and the transferred linear momentum as measure of the excitation energy. The decomposition of the LCP spectra into the pre- and post-scission components allows to determine the excitation energy remaining in FF and to estimate the scission times. Multiplicities obtained for symmetric fission and for the projectile energy of 34 AMeV agree with the data from literature. For the energy of 53 AMeV a large contribution of pre-equilibrium LCP has been observed up to the very backward angles. The results are compared with simulations including both pre-equilibrium and statistical particle emission.
^* supported by BMBF under contract 06 DR 671 D

•V.G. Tichtchenko¹, C.-M. Herbach², H.-G. Ortlepp², P. Gippner², D.V. Kamanin^2,1, Yu.E. Penionchkevich¹, K.D. Schilling² und W. Wagner² für die FOBOS-Kollaboration
¹Joint Institute for Nuclear Research, 141980 Dubna, Russia
²Research Center Rossendorf Inc., Institute for Nuclear and Hadron Physics, 01314 Dresden, Germany

The gas-filled detector array of the 4p-fragment spectrometer FOBOS has been used to measure the decay of hot heavy nuclei, characterized by a large value of Z²/A, into massive fragments. By means of incomplete fusion reactions composite systems of A » 200-250 were produced at excitation energies of e^* » 1-4 MeV/u. For each of the fragments, the mass, the kinetic energy and the emission direction are deduced from the measured data. The events from ternary decay are analyzed on the basis of the mutual emission angles and velocities of the fragment and their balances (e.g. total linear momentum, total mass, center-of-mass velocity) are compared with binary fission. Besides a dominant group of events with the lightest fragment mass A_min of approximately half the size of the projectile, which indicates some memory of the entrance channel, a nearly mass-symmetric component (A_min > 50) occurs with s » 10 mbarn. The latter will be discussed in terms of a fission-like decay process of a strongly deformed system.
^* supported by BMBF under contract 06 DR 671 D

•Matthias Eberspächer und Werner Scheid für die FOBOS-Kollaboration
Institut für Theoretische Physik, Universität Gießen, Heinrich-Buff-Ring 16, D-35392 Gießen

Es wird das modifizierte Newton-Sabatier-Verfahren zur Lösung des inversen Streuproblems bei fester Energie und gekoppelten Kanälen auf Schwerionenreaktionen angewandt. Das jetzige Verfahren setzt voraus, daß die Kopplungspotentiale nur Kanäle mit gleichen Bahndrehimpulsen verkoppeln. Diese Vorraussetzung ist fuer den Fall von Transferreaktionen zwischen Kernen mit Spin 0 erfüllt, bei denen alle Streupartner im Grundzustand bleiben. Wir stellen Anwendungen unseres Verfahrens auf einfache Modellpotentiale für ungeladene Streupartner und geladene Kerne vor.

Unterstützt durch die DFG und das Graduiertenkolleg „ Schwerionenphysik“.

•R.D. NEEF ¹, M. ARAI ², G. BAUER ³, A.S. CARROLL ⁴, H. CONRAD ¹, D. FILGES ¹, M. FUTAKAWA⁵, D. GLASGOW ⁶, J. HAINES ⁶, J. HASTINGS ⁴, Y. IKEDA ⁵, E. JERDE ⁶, Y. KIJANAGI ⁷, H. NAKASHIMA ⁵, H. SPITZER ³, H. STECHEMESSER ¹, H. TAKADA ⁵ und N. WATANABE ⁵ für die FOBOS-Kollaboration
¹FZ Jülich (Germany)
²KEK (Japan)
³PSI (Switzerland)
⁴BNL (USA)
⁵JAERI (Japan)
⁶ORNL (USA)
⁷Univ.of Hokkaido (Japan)

The proton energy range above 1 to 2 GeV for spallation targets was considered undesirable because the neutron generation in the target was suspected to become to smeared out over the depth of the target. Recent theoretical studies indicate that this effect might not be as serious as previously assumed. AGS delivers short pulsed high intensity proton beams upto 24 GeV with approximately 10¹³ ppp. The ASTE collaboration measured in a first test experiment with a mercury thick cylindrical target-diameter 20 cm and length 130 cm energy deposition (temperature rise), pressure waves effects (stress in the target containment) and neutron leakage distribution at proton beam energies of 1.5, 7.0 and 24.0 GeV. These experiments are of great relevance for the development of high intensity short pulsed neutron spallation sources as ESS (European Spallation Source) and the SNS (Spallation Neutron Source - USA). First experimental results on temperature rise and neutron leakage distributions are compared with intra-nuclear-cascade-evaporation simulations.

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