928 research outputs found
Production cross-sections and momentum distributions of fragments from neutron-deficient 36Ar at 1.05 A.GeV
We have measured production cross sections and longitudinal momentum
distributions of fragments from neutron-deficient 36Ar at 1.05 A.GeV. The
production cross-sections show excellent agreement with the predictions of the
semiempirical formula EPAX. We have compared these results, involving extremly
neutron deficient nuclei, with model calculations to extract informa tion about
the response of these models close to the driplines. The longitudinal momentum
distributions have also been extracted and are compared with the Goldhaber and
Morrissey systematics.Comment: 16 pages, 6 figure
Chiral three-nucleon forces and bound excited states in neutron-rich oxygen isotopes
We study the spectra of neutron-rich oxygen isotopes based on chiral two- and
three-nucleon interactions. First, we benchmark our many-body approach by
comparing ground-state energies to coupled-cluster results for the same
two-nucleon interaction, with overall good agreement. We then calculate bound
excited states in 21,22,23O, focusing on the role of three-nucleon forces, in
the standard sd shell and an extended sdf7/2p3/2 valence space. Chiral
three-nucleon forces provide important one- and two-body contributions between
valence neutrons. We find that both these contributions and an extended valence
space are necessary to reproduce key signatures of novel shell evolution, such
as the N = 14 magic number and the low-lying states in 21O and 23O, which are
too compressed with two-nucleon interactions only. For the extended space
calculations, this presents first work based on nuclear forces without
adjustments. Future work is needed and open questions are discussed.Comment: 6 pages, 4 figures, published versio
Breakup of loosely bound nuclei as indirect method in nuclear astrophysics: 8B, 9C, 23Al
We discuss the use of one-nucleon breakup reactions of loosely bound nuclei
at intermediate energies as an indirect method in nuclear astrophysics. These
are peripheral processes, therefore we can extract asymptotic normalization
coefficients (ANC) from which reaction rates of astrophysical interest can be
inferred. To show the usefulness of the method, three different cases are
discussed. In the first, existing experimental data for the breakup of 8B at
energies from 30 to 1000 MeV/u and of 9C at 285 MeV/u on light through heavy
targets are analyzed. Glauber model calculations in the eikonal approximation
and in the optical limit using different effective interactions give
consistent, though slightly different results, showing the limits of the
precision of the method. The results lead to the astrophysical factor
S_17(0)=18.7+/-1.9 eVb for the key reaction for solar neutrino production
7Be(p,\gamma)8B. It is consistent with the values from other indirect methods
and most direct measurements, but one. Breakup reactions can be measured with
radioactive beams as weak as a few particles per second, and therefore can be
used for cases where no direct measurements or other indirect methods for
nuclear astrophysics can be applied. We discuss a proposed use of the breakup
of the proton drip line nucleus 23Al to obtain spectroscopic information and
the stellar reaction rate for 22Mg(p,\gamma)23Al.Comment: 6 pages, 4 figures. Presented at the conference "Nuclear Physics for
Astrophysics 2", Debrecen, Hungary, May 2005. Prepared for the Proceeding
Investigation of the 6He cluster structures
The 4He+2n and t+t clustering of the 6He ground state were investigated by
means of the transfer reaction 6He(p,t)4He at 25 MeV/nucleon. The experiment
was performed in inverse kinematics at GANIL with the SPEG spectrometer coupled
to the MUST array. Experimental data for the transfer reaction were analyzed by
a DWBA calculation including the two neutrons and the triton transfer. The
couplings to the 6He --> 4He + 2n breakup channels were taken into account with
a polarization potential deduced from a coupled-discretized-continuum channels
analysis of the 6He+1H elastic scattering measured at the same time. The
influence on the calculations of the 4He+t exit potential and of the triton
sequential transfer is discussed. The final calculation gives a spectroscopic
factor close to one for the 4He+2n configuration as expected. The spectroscopic
factor obtained for the t+t configuration is much smaller than the theoretical
predictions.Comment: 10 pages, 11 figures, accepted in PR
Elastic and total reaction cross sections of oxygen isotopes in Glauber theory
We systematically calculate the total reaction cross sections of oxygen
isotopes, O, on a C target at high energies using the Glauber
theory. The oxygen isotopes are described with Slater determinants generated
from a phenomenological mean-field potential. The agreement between theory and
experiment is generally good, but a sharp increase of the reaction cross
sections from ^{21}O to ^{23}O remains unresolved. To examine the sensitivity
of the diffraction pattern of elastic scattering to the nuclear surface, we
study the differential elastic-scattering cross sections of proton-^{20,21,23}O
at the incident energy of 300 MeV by calculating the full Glauber amplitude.Comment: 9 pages, 8 figure
7Be(p,gamma)8B S-factor from ab initio wave functions
Nuclear structure of 7Be, 8B and 7,8Li is studied within the ab initio
no-core shell model (NCSM). Starting from the high-precision CD-Bonn 2000
nucleon-nucleon (NN) interaction, wave functions of 7Be and 8B bound states are
obtained in basis spaces up to 10 hbar Omega and used to calculate channel
cluster form factors (overlap integrals) of the 8B ground state with 7Be+p. Due
to the use of the harmonic oscillator (HO) basis, the overlap integrals have
incorrect asymptotic properties. We fix this problem in two alternative ways.
First, by a Woods-Saxon (WS) potential solution fit to the interior of the NCSM
overlap integrals. Second, by a direct matching with the Whittaker function.
The corrected overlap integrals are then used for the 7Be(p,gamma)8B S-factor
calculation. We study the convergence of the S-factor with respect to the NCSM
HO frequency and the model space size. Our S-factor results are in agreement
with recent direct measurement data.Comment: 4 pages, 3 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
Performance of Glass Resistive Plate Chambers for a high granularity semi-digital calorimeter
A new design of highly granular hadronic calorimeter using Glass Resistive
Plate Chambers (GRPCs) with embedded electronics has been proposed for the
future International Linear Collider (ILC) experiments. It features a 2-bit
threshold semi-digital read-out. Several GRPC prototypes with their electronics
have been successfully built and tested in pion beams. The design of these
detectors is presented along with the test results on efficiency, pad
multiplicity, stability and reproducibility.Comment: 16 pages, 15 figure
Construction and commissioning of a technological prototype of a high-granularity semi-digital hadronic calorimeter
A large prototype of 1.3m3 was designed and built as a demonstrator of the
semi-digital hadronic calorimeter (SDHCAL) concept proposed for the future ILC
experiments. The prototype is a sampling hadronic calorimeter of 48 units. Each
unit is built of an active layer made of 1m2 Glass Resistive Plate
Chamber(GRPC) detector placed inside a cassette whose walls are made of
stainless steel. The cassette contains also the electronics used to read out
the GRPC detector. The lateral granularity of the active layer is provided by
the electronics pick-up pads of 1cm2 each. The cassettes are inserted into a
self-supporting mechanical structure built also of stainless steel plates
which, with the cassettes walls, play the role of the absorber. The prototype
was designed to be very compact and important efforts were made to minimize the
number of services cables to optimize the efficiency of the Particle Flow
Algorithm techniques to be used in the future ILC experiments. The different
components of the SDHCAL prototype were studied individually and strict
criteria were applied for the final selection of these components. Basic
calibration procedures were performed after the prototype assembling. The
prototype is the first of a series of new-generation detectors equipped with a
power-pulsing mode intended to reduce the power consumption of this highly
granular detector. A dedicated acquisition system was developed to deal with
the output of more than 440000 electronics channels in both trigger and
triggerless modes. After its completion in 2011, the prototype was commissioned
using cosmic rays and particles beams at CERN.Comment: 49 pages, 41 figure
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