75 research outputs found
Dispersion of longitudinal momentum distributions induced in fragmentation reactions
On the basis of systematic measurements of fragmentation reactions, which
provide a detailed overview on the velocity distributions of residual nuclei,
an improved description of the kinematical properties of the fragmentation
residues is established. This work is dedicated to the fluctuations of their
momentum distributions. In contrast to previous investigations, limited to
close-to-projectile fragments, we extended our study to the entire production
range, down to the lightest observed fragments. In this context, beside the
contribution of abrasion and evaporation processes, we considered the effect of
the thermal break-up on the width of the momentum distributions. Using
approximated theoretical descriptions of the different reaction stages, a new
analytical formula for the variance of the momentum distribution is derived,
which is well adapted to technical applications.Comment: 14 pages, 3 figures, background info. at
http://www-wnt.gsi.de/charms
Constraint of the Nuclear Dissipation Coefficient in Fission of Hypernuclei
Experimental studies of nuclear fission induced by fusion, transfer,
spallation, fragmentation, and electromagnetic reactions in combination with
state-of-the-art calculations are successful to investigate the nuclear
dissipation mechanism in normal nuclear matter, containing only nucleons. The
dissipation mechanism has been widely studied by the use of many different
fission observables and nowadays the dissipation coefficients involved in
transport theories are well constrained. However, the existence of hypernuclei
and the possible presence of hyperons in neutron stars make it necessary to
extend the investigation of the nuclear dissipation coefficient to the
strangeness sector. In this Letter, we use fission reactions of hypernuclei to
constrain for the first time the dissipation coefficient in hypernuclear
matter, observing that this coefficient increases a factor of 6 in presence of
a single -hyperon with respect to normal nuclear matter.Comment: 6 pages, 2 figure
Experimental study of fragmentation products in the reactions 112Sn + 112Sn and 124Sn + 124Sn at 1 AGeV
Production cross-sections and longitudinal velocity distributions of the
projectile-like residues produced in the reactions 112Sn + 112Sn and 124Sn +
124Sn both at an incident beam energy of 1 AGeV were measured with the
high-resolution magnetic spectrometer, the Fragment Separator (FRS) of GSI. For
both reactions the characteristics of the velocity distributions and nuclide
production cross sections were determined for residues with atomic number Z
10. A comparison of the results of the two reactions is presented.Comment: 14 pages, 12 figure
Improved modelling of helium and tritium production for spallation targets
Reliable predictions of light charged particle production in spallation
reactions are important to correctly assess gas production in spallation
targets. In particular, the helium production yield is important for assessing
damage in the window separating the accelerator vacuum from a spallation
target, and tritium is a major contributor to the target radioactivity. Up to
now, the models available in the MCNPX transport code, including the widely
used default option Bertini-Dresner and the INCL4.2-ABLA combination of models,
were not able to correctly predict light charged particle yields. The work done
recently on both the intranuclear cascade model INCL4, in which cluster
emission through a coalescence process has been introduced, and on the
de-excitation model ABLA allows correcting these deficiencies. This paper shows
that the coalescence emission plays an important role in the tritium and
production and that the combination of the newly developed versions of the
codes, INCL4.5-ABLA07, now lead to good predictions of both helium and tritium
cross sections over a wide incident energy range. Comparisons with other
available models are also presented.Comment: 6 pages, 9 figure
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
Neutron-induced astrophysical reaction rates for translead nuclei
Neutron-induced reaction rates, including fission, are calculated in the
temperature range 1.d8 <T (K) < 1.d10 within the framework of the statistical
model for targets with atomic number 83 < Z < 119 (from Po to Uuo) from the
neutron to the proton drip-line. Four sets of rates have been calculated,
utilizing - where possible - consistent nuclear data for neutron separation
energies and fission barriers from Thomas-Fermi (TF), Extended Thomas-Fermi
plus Strutinsky Integral (ETFSI), Finite-Range Droplet Model (FRDM) and
Hartree-Fock-Bogolyubov (HFB) predictions. Tables of calculated values as well
as analytic seven parameter fits in the standard REACLIB format are supplied.
We also discuss the sensitivity of the rates to the input, aiming at a better
understanding of the uncertainties introduced by the nuclear input.Comment: 14 pages, 10 figures, 2 tables in paper, 2 in Annex and online tables
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High-precision measurement of total fission cross sections in spallation reactions of 208Pb and 238U
Total cross sections for proton- and deuteron-induced-fission of 208Pb and
238U have been determined in the energy range between 500 MeV and 1 GeV. The
experiment has been performed in inverse kinematics at GSI Darmstadt,
facilitating the counting of the projectiles and the identification of the
reaction products. High precision between 5 and 7 percent has been achieved by
individually counting the beam particles and by registering both fission
fragments in coincidence with high efficiency and full Z resolution. Fission
was clearly distinguished from other reaction channels. The results were found
to deviate by up to 30 percent from Prokofiev's systematics on total fission
cross sections. There is good agreement with an elaborate experiment performed
in direct kinematics.Comment: 18 pages, 12 figure
Systematic reduction of the proton-removal cross section in neutron-rich medium-mass nuclei
Single-neutron and single-proton removal cross sections have been measured for medium-mass neutron-rich nuclei around Z=50 and energies around 1000A MeV using the FRagment Separator (FRS) at GSI. The measured cross sections confirm the relative low values of the proton-removal cross sections, observed since a long time ago and not yet understood. Model calculations considering the knock-out process together with initial- and final-state interactions describe the measured neutron-removal cross sections. Proton-removal cross sections are, however, significantly over-predicted by the same calculations. The observed difference can be explained to a large extent by the knock-out of short-range correlated nucleons from dominant neutron-proton pairs in neutron-rich nuclei. © 2020 The Author(s)Peer reviewe
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