117 research outputs found
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
Search for low lying dipole strength in the neutron rich nucleus Ne
Coulomb excitation of the exotic neutron-rich nucleus Ne on a
Pb target was measured at 58 A.MeV in order to search for low-lying E1
strength above the neutron emission threshold. Data were also taken on an
Al target to estimate the nuclear contribution. The radioactive beam
was produced by fragmentation of a 95 A.MeV Ar beam delivered by the
RIKEN Research Facility. The set-up included a NaI gamma-ray array, a charged
fragment hodoscope and a neutron wall. Using the invariant mass method in the
Ne+n channel, we observe a sizable amount of E1 strength between 6 and
10 MeV. The reconstructed Ne angular distribution confirms its E1
nature. A reduced dipole transition probability of B(E1)=0.490.16
is deduced. For the first time, the decay pattern of low-lying
strength in a neutron-rich nucleus is obtained. The results are discussed in
terms of a pygmy resonance centered around 9 MeV
Collective excitations in the Unitary Correlation Operator Method and relativistic QRPA studies of exotic nuclei
The collective excitation phenomena in atomic nuclei are studied in two
different formulations of the Random Phase Approximation (RPA): (i) RPA based
on correlated realistic nucleon-nucleon interactions constructed within the
Unitary Correlation Operator Method (UCOM), and (ii) relativistic RPA (RRPA)
derived from effective Lagrangians with density-dependent meson-exchange
interactions. The former includes the dominant interaction-induced short-range
central and tensor correlations by means of an unitary transformation. It is
shown that UCOM-RPA correlations induced by collective nuclear vibrations
recover a part of the residual long-range correlations that are not explicitly
included in the UCOM Hartree-Fock ground state. Both RPA models are employed in
studies of the isoscalar monopole resonance (ISGMR) in closed-shell nuclei
across the nuclide chart, with an emphasis on the sensitivity of its properties
on the constraints for the range of the UCOM correlation functions. Within the
Relativistic Quasiparticle RPA (RQRPA) based on Relativistic Hartree-Bogoliubov
model, the occurrence of pronounced low-lying dipole excitations is predicted
in nuclei towards the proton drip-line. From the analysis of the transition
densities and the structure of the RQRPA amplitudes, it is shown that these
states correspond to the proton pygmy dipole resonance.Comment: 15 pages, 4 figures, submitted to Physics of Atomic Nuclei,
conference proceedings, "Frontiers in the Physics of Nucleus", St.
Petersburg, 28. June-1. July, 200
Direct determination of photodisintegration cross sections and the p-process
Photon-induced reactions play a key role in the nucleosynthesis of heavy
neutron-deficient nuclei, the so-called p-nuclei. In this paper we review the
present status of experiments on photon-induced reactions at energies of
astrophysical importance and their relevance to p-process modeling.Comment: Nucl. Phys. A, in pres
Relativistic Random-Phase Approximation with density-dependent meson-nucleon couplings
The matrix equations of the relativistic random-phase approximation (RRPA)
are derived for an effective Lagrangian characterized by density-dependent
meson-nucleon vertex functions. The explicit density dependence of the
meson-nucleon couplings introduces rearrangement terms in the residual two-body
interaction, that are essential for a quantitative description of excited
states. Illustrative calculations of the isoscalar monopole, isovector dipole
and isoscalar quadrupole response of Pb, are performed in the fully
self-consistent RRPA framework, based on effective interactions with a
phenomenological density dependence adjusted to nuclear matter and ground-state
properties of spherical nuclei. The comparison of the RRPA results on multipole
giant resonances with experimental data constrains the parameters that
characterize the isoscalar and isovector channel of the density-dependent
effective interactions.Comment: RevTeX, 8 eps figures, submitted to Phys. Rev.
Linear Responses in Time-dependent Hartree-Fock-Bogoliubov Method with Gogny Interaction
A numerical method to integrate the time-dependent Hartree-Fock Bogoliubov
(TDHFB) equations with Gogny interaction is proposed. The feasibility of the
TDHFB code is illustrated by the conservation of the energy, particle numbers,
and center-of-mass in the small amplitude vibrations of oxygen 20. The TDHFB
code is applied to the isoscalar quadrupole and/or isovector dipole vibrations
in the linear (small amplitude) region in oxygen isotopes (masses A = 18,20,22
and 24), titanium isotopes (A = 44,50,52 and 54), neon isotope (A = 26), and
magnesium isotopes (A = 24 and 34). The isoscalar quadrupole and isovector
dipole strength functions are calculated from the expectation values of the
isoscalar quadrupole and isovector dipole moments.Comment: 10 pages, 13 figure
Mass measurements of 60–63Ga reduce x-ray burst model uncertainties and extend the evaluated T=1 isobaric multiplet mass equation
We report precision mass measurements of neutron-deficient gallium isotopes approaching the proton drip line. The measurements of Ga60–63 performed with the TITAN multiple-reflection time-of-flight mass spectrometer provide a more than threefold improvement over the current literature mass uncertainty of Ga61 and mark the first direct mass measurement of Ga60. The improved precision of the Ga61 mass has important implications for the astrophysical rp process, as it constrains essential reaction Q values near the Zn60 waiting point. Based on calculations with a one-zone model, we demonstrate the impact of the improved mass data on prediction uncertainties of x-ray burst models. The first-time measurement of the Ga60 ground-state mass establishes the proton-bound nature of this nuclide, thus constraining the location of the proton drip line along this isotopic chain. Including the measured mass of Ga60 further enables us to extend the evaluated T=1 isobaric multiplet mass equation up to A=60
Investigating nuclear structure near N=32 and N=34: Precision mass measurements of neutron-rich Ca, Ti, and V isotopes
Nuclear mass measurements of isotopes are key to improving our understanding of nuclear structure across the chart of nuclides, in particular, for the determination of the appearance or disappearance of nuclear shell closures. We present high-precision mass measurements of neutron-rich Ca, Ti, and V isotopes performed at TRIUMF's Ion Trap for Atomic and Nuclear science (TITAN) and the Low Energy Beam and Ion Trap (LEBIT) facilities. These measurements were made using the TITAN multiple-reflection time-of-flight mass spectrometer (MR-ToF-MS) and the LEBIT 9.4T Penning trap mass spectrometer. In total, 13 masses were measured, 8 of which represent increases in precision over previous measurements. These measurements refine trends in the mass surface around N=32 and N=34, and support the disappearance of the N=32 shell closure with increasing proton number. Additionally, our data do not support the presence of a shell closure at N=34.Nuclear mass measurements of isotopes are key to improving our understanding of nuclear structure across the chart of nuclides, in particular for the determination of the appearance or disappearance of nuclear shell closures. We present high-precision mass measurements of neutron-rich Ca, Ti and V isotopes performed at the TITAN and LEBIT facilities. These measurements were made using the TITAN multiple-reflection time-of-flight mass spectrometer (MR-ToF-MS) and the LEBIT 9.4T Penning trap mass spectrometer. In total, 13 masses were measured, eight of which represent increases in precision over previous measurements. These measurements refine trends in the mass surface around and , and support the disappearance of the shell closure with increasing proton number. Additionally, our data does not support the presence of a shell closure at
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