119 research outputs found
Experimental Indications for the Response of the Spectators to the Participant Blast
Precise momentum distributions of identified projectile fragments, formed in
the reactions 238U + Pb and 238U + Ti at 1 A GeV, are measured with a
high-resolution magnetic spectrometer. With increasing mass loss, the
velocities first decrease as expected from previously established systematics,
then level off, and finally increase again. Light fragments are on the average
even faster than the projectiles. This finding is interpreted as the response
of the spectators to the participant blast. The re-acceleration of projectile
spectators is sensitive to the nuclear mean field and provides a new tool for
investigating the equation of state of nuclear matter.Comment: 7 pages, 3 figures, background information on
http://www-wnt.gsi.de/kschmidt
Ion-lithium collision dynamics studied with an in-ring MOTReMi
We present a novel experimental tool allowing for kinematically complete
studies of break-up processes of laser-cooled atoms. This apparatus, the
'MOTReMi', is a combination of a magneto-optical trap (MOT) and a Reaction
Microscope (ReMi). Operated in an ion-storage ring, the new setup enables to
study the dynamics in swift ion-atom collisions on an unprecedented level of
precision and detail. In first experiments on collisions with 1.5 MeV/amu
O-Li the pure ionization of the valence electron as well as
ionization-excitation of the lithium target has been investigated
Breakup Conditions of Projectile Spectators from Dynamical Observables
Momenta and masses of heavy projectile fragments (Z >= 8), produced in
collisions of 197Au with C, Al, Cu and Pb targets at E/A = 600 MeV, were
determined with the ALADIN magnetic spectrometer at SIS. An analysis of
kinematic correlations between the two and three heaviest projectile fragments
in their rest frame was performed. The sensitivity of these correlations to the
conditions at breakup was verified within the schematic SOS-model. The data
were compared to calculations with statistical multifragmentation models and to
classical three-body calculations. Classical trajectory calculations reproduce
the dynamical observables. The deduced breakup parameters, however, differ
considerably from those assumed in the statistical multifragmentation models
which describe the charge correlations. If, on the other hand, the analysis of
kinematic and charge correlations is performed for events with two and three
heavy fragments produced by statistical multifragmentation codes, a good
agreement with the data is found with the exception that the fluctuation widths
of the intrinsic fragment energies are significantly underestimated. A new
version of the multifragmentation code MCFRAG was therefore used to investigate
the potential role of angular momentum at the breakup stage. If a mean angular
momentum of 0.75/nucleon is added to the system, the energy fluctuations
can be reproduced, but at the same time the charge partitions are modified and
deviate from the data.
PACS numbers: 25.70.Mn, 25.70.Pq, 25.75.Ld, 25.75.-qComment: 38 pages, RevTeX with 21 included figures; Also available from
http://www-kp3.gsi.de/www/kp3/aladin_publications.htm
Recoil Studies in the Reaction of 12-C Ions with the Enriched Isotope 118-Sn
The recoil properties of the product nuclei from the interaction of 2.2
GeV/nucleon 12-C ions from Nuclotron of the Laboratory of High Energies (LHE),
Joint Institute for Nuclear Research (JINR) at Dubna with a 118-Sn target have
been studied using catcher foils. The experimental data were analyzed using the
mathematical formalism of the standard two-step vector model. The results for
12-C ions are compared with those for deuterons and protons. Three different
Los Alamos versions of the Quark-Gluon String Model (LAQGSM) were used for
comparison with our experimental data.Comment: 10 pages, 6 figures, submitted to Nucl. Phys.
Breakup Temperature of Target Spectators in Au + Au Collisions at E/A = 1000 MeV
Breakup temperatures were deduced from double ratios of isotope yields for
target spectators produced in the reaction Au + Au at 1000 MeV per nucleon.
Pairs of He and Li isotopes and pairs of He and H
isotopes (p, d and d, t) yield consistent temperatures after feeding
corrections, based on the quantum statistical model, are applied. The
temperatures rise with decreasing impact parameter from 4 MeV for peripheral to
about 10 MeV for the most central collisions.
The good agreement with the breakup temperatures measured previously for
projectile spectators at an incident energy of 600 MeV per nucleon confirms the
observed universality of the spectator decay at relativistic bombarding
energies. The measured temperatures also agree with the breakup temperatures
predicted by the statistical multifragmentation model. For these calculations a
relation between the initial excitation energy and mass was derived which gives
good simultaneous agreement for the fragment charge correlations.
The energy spectra of light charged particles, measured at =
150, exhibit Maxwellian shapes with inverse slope parameters much
higher than the breakup temperatures. The statistical multifragmentation model,
because Coulomb repulsion and sequential decay processes are included, yields
light-particle spectra with inverse slope parameters higher than the breakup
temperatures but considerably below the measured values. The systematic
behavior of the differences suggests that they are caused by
light-charged-particle emission prior to the final breakup stage.
PACS numbers: 25.70.Mn, 25.70.Pq, 25.75.-qComment: 29 pages, TeX with 11 included figures; Revised version accepted for
publication in Z. Phys. A Two additional figure
Target electron ionization in Li2+-Li collisions: A multi-electron perspective
Target electron removal in Li2+-Li collisions at 2290 keV/amu is studied experimentally and theoretically for ground and excited lithium target configurations. It is shown that in outer-shell ionization a single-electron process plays the dominant part. However, the K-shell ionization results are more difficult to interpret. According to our calculations, the process is shown to be strongly single-particle like. On one hand, a high resemblance between theoretical single-particle ionization and exclusive inner-shell ionization is demonstrated, and contributions from multi-electron processes are found to be weak. On the other hand, it is indicated by the discrepancy between experimental and single-particle theoretical results that multi-electron processes involving ionization from the outer-shell may play a crucial role
Liquid-gas phase transition in nuclear multifragmentation
The equation of state of nuclear matter suggests that at suitable beam
energies the disassembling hot system formed in heavy ion collisions will pass
through a liquid-gas coexistence region. Searching for the signatures of the
phase transition has been a very important focal point of experimental
endeavours in heavy ion collisions, in the last fifteen years. Simultaneously
theoretical models have been developed to provide information about the
equation of state and reaction mechanisms consistent with the experimental
observables. This article is a review of this endeavour.Comment: 63 pages, 27 figures, submitted to Adv. Nucl. Phys. Some typos
corrected, minor text change
Breakup Density in Spectator Fragmentation
Proton-proton correlations and correlations of protons, deuterons and tritons
with alpha particles from spectator decays following 197Au + 197Au collisions
at 1000 MeV per nucleon have been measured with two highly efficient detector
hodoscopes. The constructed correlation functions, interpreted within the
approximation of a simultaneous volume decay, indicate a moderate expansion and
low breakup densities, similar to assumptions made in statistical
multifragmentation models.
PACS numbers: 25.70.Pq, 21.65.+f, 25.70.Mn, 25.75.GzComment: 11 pages, LaTeX with 3 included figures; Also available from
http://www-kp3.gsi.de/www/kp3/aladin_publications.htm
Statistical signatures of critical behavior in small systems
The cluster distributions of different systems are examined to search for
signatures of a continuous phase transition. In a system known to possess such
a phase transition, both sensitive and insensitive signatures are present;
while in systems known not to possess such a phase transition, only insensitive
signatures are present. It is shown that nuclear multifragmentation results in
cluster distributions belonging to the former category, suggesting that the
fragments are the result of a continuous phase transition.Comment: 31 pages, two columns with 30 figure
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