345 research outputs found
Double Giant Dipole Resonance in ^{208}Pb
Double-dipole excitations in ^{208}Pb are analyzed within a microscopic model
explicitly treating 2p2h-excitations. Collective states built from such
2p2h-excitations are shown to appear at about twice the energy of the isovector
giant dipole resonance, in agreement with the experimental findings. The
calculated cross section for Coulomb excitation at relativistic energies cannot
explain simultaneously the measured single-dipole and double-dipole cross
sections, however.Comment: 7 pages, Latex, 5 postscript figure
Response of Multi-strip Multi-gap Resistive Plate Chamber
A prototype of Multi-strip Multi-gap Resistive Plate chamber (MMRPC) with
active area 40 cm 20 cm has been developed at SINP, Kolkata. Detailed
response of the developed detector was studied with the pulsed electron beam
from ELBE at Helmholtz-Zentrum Dresden-Rossendorf. In this report the response
of SINP developed MMRPC with different controlling parameters is described in
details. The obtained time resolution () of the detector after slew
correction was 91.53 ps. Position resolution measured along ()
and across () the strip was 2.80.6 cm and 0.58 cm, respectively.
The measured absolute efficiency of the detector for minimum ionizing particle
like electron was 95.81.3 . Better timing resolution of the detector
can be achieved by restricting the events to a single strip. The response of
the detector was mainly in avalanche mode but a few percentage of streamer mode
response was also observed. A comparison of the response of these two modes
with trigger rate was studiedComment: 19 pages, 26 figure
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
Efficiency determination of resistive plate chambers for fast quasi-monoenergetic neutrons
Composite detectors made of stainless steel converters and multigap resistive
plate chambers have been irradiated with quasi-monoenergetic neutrons with a
peak energy of 175MeV. The neutron detection efficiency has been determined
using two different methods. The data are in agreement with the output of Monte
Carlo simulations. The simulations are then extended to study the response of a
hypothetical array made of these detectors to energetic neutrons from a
radioactive ion beam experiment.Comment: Submitted to Eur.Phys.J. A; upgraded version correcting some typos
and updating ref.
Anharmonic collective excitation in a solvable model
We apply the time-dependent variational principle, the nuclear field theory,
and the boson expansion method to the Lipkin model to discuss anharmonicities
of collective vibrational excitations. It is shown that all of these approaches
lead to the same anharmonicity to leading order in the number of particles.
Comparison with the exact solution of the Lipkin model shows that these
theories reproduce it quite well.Comment: RevTex, 18 pages, 4 postscript figure
First Measurement of the 96Ru(p, γ)97Rh Cross Section for the p-Process with a Storage Ring
This work presents a direct measurement of the 96Ru(p, γ)97Rh cross section via a novel technique using a storage ring, which opens opportunities for reaction measurements on unstable nuclei. A proof-of-principle experiment was performed at the storage ring ESR at GSI in Darmstadt, where circulating 96 Ru ions interacted repeatedly with a hydrogen target. The 96Ru(p, γ)97Rh cross section between 9 and 11 MeV has been determined using two independent normalization methods. As key ingredients in Hauser-Feshbach calculations, the γ-ray strength function as well as the level density model can be pinned down with the measured (p, γ) cross section. Furthermore, the proton optical potential can be optimized after the uncertainties from the γ-ray strength function and the level density have been removed. As a result, a constrained 96 Ru(p, γ)97Rh reaction rate over a wide temperature range is recommended for p-process network calculations
Anharmonicities of giant dipole excitations
The role of anharmonic effects on the excitation of the double giant dipole
resonance is investigated in a simple macroscopic model.Perturbation theory is
used to find energies and wave functions of the anharmonic ascillator.The cross
sections for the electromagnetic excitation of the one- and two-phonon giant
dipole resonances in energetic heavy-ion collisions are then evaluated through
a semiclassical coupled-channel calculation.It is argued that the variations of
the strength of the anharmonic potential should be combined with appropriate
changes in the oscillator frequency,in order to keep the giant dipole resonance
energy consistent with the experimental value.When this is taken into
account,the effects of anharmonicities on the double giant dipole resonance
excitation probabilities are small and cannot account for the well-known
discrepancy between theory and experiment
Double giant resonances in deformed nuclei
We report on the first microscopic study of the properties of two-phonon
giant resonances in deformed nuclei. The cross sections of the excitation of
the giant dipole and the double giant dipole resonances in relativistic heavy
ion collisions are calculated. We predict that the double giant dipole
resonance has a one-bump structure with a centroid 0.8 MeV higher than twice
energy for the single giant dipole resonance in the reaction under
consideration. The width of the double resonance equals to 1.33 of that for the
single resonance.Comment: 5 pages, 2 postscript figure
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