457 research outputs found
Modified Empirical Parametrization of Fragmentation Cross Sections
New experimental data obtained mainly at the GSI/FRS facility allow to modify
the empirical parametrization of fragmentation cross sections, EPAX. It will be
shown that minor modifications of the parameters lead to a much better
reproduction of measured cross sections. The most significant changes refer to
the description of fragmentation yields close to the projectile and of the
memory effect of neutron-deficient projectiles.Comment: 10 pages, latex file, 11 postscript figures, submitted to Phys. Rev.
Production of neutron-rich nuclei in fragmentation reactions of 132Sn projectiles at relativistic energies
The fragmentation of neutron-rich 132Sn nuclei produced in the fission of
238U projectiles at 950 MeV/u has been investigated at the FRagment Separator
(FRS) at GSI. This work represents the first investigation of fragmentation of
medium-mass radioactive projectiles with a large neutron excess. The measured
production cross sections of the residual nuclei are relevant for the possible
use of a two-stage reaction scheme (fission+fragmentation) for the production
of extremely neutron-rich medium-mass nuclei in future rare-ion-beam
facilities. Moreover, the new data will provide a better understanding of the
"memory" effect in fragmentation reactions.Comment: 5 pages, 3 figure
Projectile fragmentation of 129Xe at Elab=790 AMeV
We have measured production yields and longitudinal momentum distributions of
projectile-like fragments in the reaction 129Xe + 27Al at an energy of Elab=790
AMeV. Production cross sections higher than expected from systematics were
observed for nuclei in the neutron-deficient tails of the isotopic
distributions. A comparison with previously measured data from the
fragmentation of 136Xe ions shows that the production yields strongly depend on
the neutron excess of the projectile with respect to the line of
beta-stability. The momentum distributions exhibit a dependence on the fragment
neutron-to-proton ratio in isobaric chains, which was not expected from
systematics so far. This can be interpreted by a higher excitation of the
projectile during the formation of neutron-deficient fragments.Comment: 21 pages, 8 figures, 1 tabl
Evaporation residues produced in spallation of 208Pb by protons at 500A MeV
The production cross sections of fragmentation-evaporation residues in the
reaction Pb+p at 500A MeV have been measured using the inverse-kinematics
method and the FRS spectrometer (GSI). Fragments were identified in nuclear
charge using ionisation chambers. The mass identification was performed
event-by-event using the B-rho - TOF - Delta-E technique. Although
partially-unresolved ionic charge states induced an ambiguity on the mass of
some heavy fragments, production rates could be obtained with a high accuracy
by systematically accounting for the polluting ionic charge states. The
contribution of multiple reactions in the target was subtracted using a new,
partly self-consistent code. The isobaric distributions are found to have a
shape very close to the one observed in experiments at higher energy. Kinematic
properties of the fragments were also measured. The total and the isotopic
cross sections, including charge-pickup cross sections, are in good agreement
with previous measurements. The data are discussed in the light of previous
spallation measurements, especially on lead at 1 GeV
Fragmentation of exotic oxygen isotopes
Abrasion-ablation models and the empirical EPAX parametrization of projectile fragmentation are described. Their cross section predictions are compared to recent data of the fragmentation of secondary beams of neutron-rich, unstable 19,20,21O isotopes at beam energies near 600 MeV/nucleon as well as data for stable 17,18O beams
Observation of two-proton radioactivity of Mg19 by tracking the decay products
We have observed the two-proton radioactivity of the previously unknown 19Mg ground state by tracking the decay products in-flight. For the first time, the trajectories of the 2p-decay products, 17Ne+p+p, have been measured by using tracking microstrip detectors which allowed us to reconstruct the 2p-decay vertices and fragment correlations. The half-life of 19Mg deduced from the measured vertex distribution is 4.0(15) ps in the system of 19Mg. The Q value of the 2p decay of the 19Mg ground state inferred from the measured p−p−17Ne correlations is 0.75(5) MeV.MEC FPA2003-05958 FPA2006-13807-C02-0
Production of Neutron-rich Heavy Residues and the Freeze-out Temperature in the Fragmentation of Relativistic 238U Projectiles Determined by the Isospin Thermometer
Isotope yields of heavy residues produced in collisions of 238U with lead at
1AGeV show indications for a simultaneous break-up process. From the average
N-over-Z ratio of the final residues up to Z = 70, the average limiting
temperature of the break-up configuration at freeze out was determined to T
approximately 5 MeV using the isospin-thermometer method. Consequences for the
understanding of other phenomena in highly excited nuclear systems are
discussed.Comment: 22 pages, 9 figures, accepted by Nucl. Phys.
Spectroscopy of proton-unbound nuclei by tracking their decay products in-flight: One- and twoproton decays of 15F, 16Ne, and 19Na
A powerful method of investigating proton-unbound nuclear states by tracking their decay products in flight is discussed in detail. To verify the method, four known levels in 15F, 16Ne, and 19Na were investigated by measuring the angular correlations between protons and the respective heavy-ion fragments stemming from the precursor decays in flight. The parent nuclei of interest were produced in nuclear reactions of one-neutron removal from 17Ne and 20Mg projectiles at energies of 410-450 A MeV. The trajectories of the respective decay products, 14O+p+p and 18Ne+p+p, were measured by applying a tracking technique with microstrip detectors. These data were used to reconstruct the angular correlations of the fragments, which provided information on energies and widths of the parent states. In addition for reproducing properties of known states, evidence for hitherto unknown excited states in 15F and 16Ne was found. This tracking technique has an advantage in studies of exotic nuclei beyond the proton drip line measuring the resonance energies and widths with a high precision although by using low-intensity beams and very thick targets.EURONS EC-I3 FPA2006-13807-C02-01 FPA2007-6307
Measurement of residual nucleus cross sections and recoil energies in p + Fe collisions at 300, 500, 750, 1000 and 1500 MeV
The production of residual nuclei in p + Fe collisions has been measured at GSI on the FRS facility by means of the reverse kinematic techniques at 300, 500, 750, 1000 and 1500 MeV/A. The cross-sections larger than 0.01 mb of all isotopes with Z larger than 8 have been obtained. Velocity distributions were also measured. Comparisons to models describing spallation reactions and some empirical formulae often used in astrophysics are presented. These data are directly used to calculate impurety production and DPAs in a thin window as foreseen in spallation sources or accelerator-driven systems
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