724 research outputs found
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
Resonance capture cross section of 207Pb
The radiative neutron capture cross section of 207Pb has been measured at the
CERN neutron time of flight installation n_TOF using the pulse height weighting
technique in the resolved energy region. The measurement has been performed
with an optimized setup of two C6D6 scintillation detectors, which allowed us
to reduce scattered neutron backgrounds down to a negligible level. Resonance
parameters and radiative kernels have been determined for 16 resonances by
means of an R-matrix analysis in the neutron energy range from 3 keV to 320
keV. Good agreement with previous measurements was found at low neutron
energies, whereas substantial discrepancies appear beyond 45 keV. With the
present results, we obtain an s-process contribution of 77(8)% to the solar
abundance of 207Pb. This corresponds to an r-process component of 23(8)%, which
is important for deriving the U/Th ages of metal poor halo stars.Comment: 7 pages, 3 figures, to be published in Phys. Rev.
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
Nuclear astrophysics with radioactive ions at FAIR
R. Reifarth et al: ; 12 págs.; 9 figs.; Open Access funded by Creative Commons Atribution Licence 3.0 ; Nuclear Physics in Astrophysics VI (NPA6)The nucleosynthesis of elements beyond iron is dominated by neutron captures
in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during
those processes, because they are shielded from the s-process
ow and r-process -decay chains.
These nuclei are attributed to the p and rp process.
For all those processes, current research in nuclear astrophysics addresses the need for more
precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct
or inverse kinematics, forward or time-reversed direction are investigated to determine or at least
to constrain the desired reaction cross sections.
The Facility for Antiproton and Ion Research (FAIR) will oer unique, unprecedented
opportunities to investigate many of the important reactions. The high yield of radioactive
isotopes, even far away from the valley of stability, allows the investigation of isotopes involved
in processes as exotic as the r or rp processes.This project was supported by the HGF Young Investigators Project VH-NG-327, EMMI, H4F,
HGS-HIRe, JINA, NAVI, DFG and ATHENA.Peer Reviewe
Measurement of the neutron capture cross section of the s-only isotope 204Pb from 1 eV to 440 keV
The neutron capture cross section of 204Pb has been measured at the CERN
n_TOF installation with high resolution in the energy range from 1 eV to 440
keV. An R-matrix analysis of the resolved resonance region, between 1 eV and
100 keV, was carried out using the SAMMY code. In the interval between 100 keV
and 440 keV we report the average capture cross section. The background in the
entire neutron energy range could be reliably determined from the measurement
of a 208Pb sample. Other systematic effects in this measurement could be
investigated and precisely corrected by means of detailed Monte Carlo
simulations. We obtain a Maxwellian average capture cross section for 204Pb at
kT=30 keV of 79(3) mb, in agreement with previous experiments. However our
cross section at kT=5 keV is about 35% larger than the values reported so far.
The implications of the new cross section for the s-process abundance
contributions in the Pb/Bi region are discussed.Comment: 8 pages, 3 figures, article submitted to Phys. Rev.
New measurement of neutron capture resonances of 209Bi
The neutron capture cross section of Bi209 has been measured at the CERN n
TOF facility by employing the pulse-height-weighting technique. Improvements
over previous measurements are mainly because of an optimized detection system,
which led to a practically negligible neutron sensitivity. Additional
experimental sources of systematic error, such as the electronic threshold in
the detectors, summing of gamma-rays, internal electron conversion, and the
isomeric state in bismuth, have been taken into account. Gamma-ray absorption
effects inside the sample have been corrected by employing a nonpolynomial
weighting function. Because Bi209 is the last stable isotope in the reaction
path of the stellar s-process, the Maxwellian averaged capture cross section is
important for the recycling of the reaction flow by alpha-decays. In the
relevant stellar range of thermal energies between kT=5 and 8 keV our new
capture rate is about 16% higher than the presently accepted value used for
nucleosynthesis calculations. At this low temperature an important part of the
heavy Pb-Bi isotopes are supposed to be synthesized by the s-process in the He
shells of low mass, thermally pulsing asymptotic giant branch stars. With the
improved set of cross sections we obtain an s-process fraction of 19(3)% of the
solar bismuth abundance, resulting in an r-process residual of 81(3)%. The
present (n,gamma) cross-section measurement is also of relevance for the design
of accelerator driven systems based on a liquid metal Pb/Bi spallation target.Comment: 10 pages, 5figures, recently published in Phys. Rev.
βDelayed γRay spectroscopy of heavy neutron rich nuclei “south” of lead
Relativistic projectile fragmentation of a 208Pb primary beam has been used to produce neutron-rich nuclei with proton-holes relative to the Z = 82 shell closure, i.e., “south” of Pb. βDelayed γRay spectroscopy allows to investigate the structural properties of such nuclei with A ~ 195 → 205. The current work presents transitions de-exciting excited states in 204Au, which are the first spectroscopic information on this N = 125 isotone.Agramunt Ros, Jorge, [email protected] ; Algora, Alejandro, [email protected] ; Molina Palacios, Francisco Manuel, [email protected] ; Rubio Barroso, Berta, [email protected]
Coulomb breakup of 17 Ne from the view point of nuclear astrophysics
6 pags., 5 figs. -- XII International Symposium on Nuclei in the Cosmos, August 5-12, 2012, Cairns, AustraliaBy the Coulomb breakup of 17Ne, the time-reversed reaction 15O(2p, γ) 17Ne has been studied.
This reaction might play an important role in the rp process, as a break-out reaction of the hot
CNO cycle. The secondary 17Ne ion beam with an energy of 500 MeV/nucleon has been dissociated in a Pb target. The reaction products have been detected with the LAND-R3B experimental
setup at GSI. The preliminary differential and integral Coulomb dissociation cross section σCoul
has been determined, which then will be converted into a photo-absorption cross section σphoto,
and a two-proton radiative capture cross section σcap. Additionally, information about the structure of the 17Ne, a potential two-proton halo nucleus, will be received. The analysis is in progress.This project was supported by the German Federal Ministry for Education and Research
(BMBF), EU(EURONS), EMMI-GSI, and HIC for FAI
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