29 research outputs found
Coincidence measurement of residues and light particles in the reaction 56Fe+p at 1 GeV per nucleon with SPALADIN
The spallation of Fe in collisions with hydrogen at 1 A GeV has been
studied in inverse kinematics with the large-aperture setup SPALADIN at GSI.
Coincidences of residues with low-center-of-mass kinetic energy light particles
and fragments have been measured allowing the decomposition of the total
reaction cross-section into the different possible de-excitation channels.
Detailed information on the evolution of these de-excitation channels with
excitation energy has also been obtained. The comparison of the data with
predictions of several de-excitation models coupled to the INCL4 intra-nuclear
cascade model shows that only GEMINI can reasonably account for the bulk of
collected results, indicating that in a light system with no compression and
little angular momentum, multifragmentation might not be necessary to explain
the data.Comment: 4 pages, 5 figures, revised version accepted in Phys. Rev. Let
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
124Sn and radioactive beams of 124La and 107Sn 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 (\Delta T \approx 0.6 MeV) appear for residue
production near the onset of multifragmentation.Comment: 11 pages, 3 figures, accepted for publ. in Phys. Rev. Let
Tracing a phase transition with fluctuations of the largest fragment size: Statistical multifragmentation models and the ALADIN S254 data
A phase transition signature associated with cumulants of the largest
fragment size distribution has been identified in statistical
multifragmentation models and examined in analysis of the ALADIN S254 data on
fragmentation of neutron-poor and neutron-rich projectiles. Characteristics of
the transition point indicated by this signature are weakly dependent on the
A/Z ratio of the fragmenting spectator source. In particular, chemical
freeze-out temperatures are estimated within the range 5.9 to 6.5 MeV. The
experimental results are well reproduced by the SMM model.Comment: 7 pages, 3 figures, Proceedings of the International Workshop on
Multifragmentation and Related Topics (IWM2009), Catania, Italy, November
2009
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 124La and 107Sn were selected to study the isospin
dependence of the limiting temperature of heavy nuclei by comparing with
results for stable 124Sn 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.Comment: 6 pages, 7 eps figures, elsart, submitted to Nucl. Instr. and Meth.
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.Comment: 6 pages, 4 figures, IX International Conference on Nucleus-Nucleus
Collisions, Rio de Janeiro, Brazil, August 28 - September 1, 200
Isospin dependent multifragmentation of relativistic projectiles
The N/Z dependence of projectile fragmentation at relativistic energies has
been studied with the ALADIN forward spectrometer at the GSI Schwerionen
Synchrotron (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. For the interpretation of the data, calculations with
the statistical multifragmentation model for a properly chosen ensemble of
excited sources were performed. The parameters of the ensemble, representing
the variety of excited spectator nuclei expected in a participant-spectator
scenario, are determined empirically by searching for an optimum reproduction
of the measured fragment-charge distributions and correlations. An overall very
good agreement is obtained. The possible modification of the liquid-drop
parameters of the fragment description in the hot freeze-out environment is
studied, and a significant reduction of the symmetry-term coefficient is found
necessary to reproduce the mean neutron-to-proton ratios /Z and the
isoscaling parameters of Z<=10 fragments. The calculations are, furthermore,
used to address open questions regarding the modification of the surface-term
coefficient at freeze-out, the N/Z dependence of the nuclear caloric curve, and
the isotopic evolution of the spectator system between its formation during the
initial cascade stage of the reaction and its subsequent breakup.Comment: 23 pages, 29 figures, published in Physical Review
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.Comment: 10 pages,7 figure, 18th Nuclear Physics Division Conference of the
EPS, Prague, submitted to Nucl. Phys.
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.Comment: 16 pages, 8 figure
Mass measurement and isoscaling in Sn+Sn and Sn+Sn reactions at 600 AMeV
Isotopic effects in projectile spectator fragmentation at 600 AMeV have been investigated using data collected in recent experiments with SIS beams at the GSI laboratory and with the ALADiN forward-spectrometer. For this purpose, primary beams of 124Sn, as well as secondary beams of 124La and 107Sn produced at the FRS fragment separator have been used. Isoscaling in 124,107Sn+Sn reactions is investigated and results are compared with data taken with the INDRA multidetector for 12C+112,124Sn reactions
Exclusive measurements on Fe+p at 1 A Gev with the SPALADIN setup at GSI
A new type of spallation experiments has been carried out at GSI, Darmstadt (Germany) in order to understand the spallation mechanism in greater details. These experiments use the inverse-kinematics technique where the ion beam is directed onto a liquid Hydrogen target, allowing the detection of heavy spallation residues in coincidence with low center-of-mass energy light particles. The setup is based on A Large Acceptance DIpole magNet (ALADIN) coupled with a multitrack Time Projection Chamber (TPC), a hodoscope and a neutron detector. First, data on Fe+p at 1 A GeV were taken in February 2004. In the on-going analysis, isotopic cross-sections have been determined and compared to data taken at the FRagment Separator in GSI. Mean values and width of residue velocity distributions have also been obtained as well as Helium production cross-section. First, coincidence data are being analyzed