327 research outputs found
Spectroscopy of P using the one-proton knockout reaction
The structure of P was studied with a one-proton knockout reaction
at88~MeV/u from a S projectile beam at NSCL. The rays from
thedepopulation of excited states in P were detected with GRETINA,
whilethe P nuclei were identified event-by-event in the focal plane of
theS800 spectrograph. The level scheme of P was deduced up to 7.5 MeV
using coincidences. The observed levels were attributed to
protonremovals from the -shell and also from the deeply-bound
orbital.The orbital angular momentum of each state was derived from the
comparisonbetween experimental and calculated shapes of individual
(-gated)parallel momentum distributions. Despite the use of different
reactions andtheir associate models, spectroscopic factors, , derived
from theS knockout reaction agree with those obtained earlier
fromS(,\nuc{3}{He}) transfer, if a reduction factor , as
deducedfrom inclusive one-nucleon removal cross sections, is applied to the
knockout transitions.In addition to the expected proton-hole configurations,
other states were observedwith individual cross sections of the order of
0.5~mb. Based on their shiftedparallel momentum distributions, their decay
modes to negative parity states,their high excitation energy (around 4.7~MeV)
and the fact that they were notobserved in the (,\nuc{3}{He}) reaction, we
propose that they may resultfrom a two-step mechanism or a nucleon-exchange
reaction with subsequent neutronevaporation. Regardless of the mechanism, that
could not yet be clarified, thesestates likely correspond to neutron core
excitations in \nuc{35}{P}. Thisnewly-identified pathway, although weak, offers
the possibility to selectivelypopulate certain intruder configurations that are
otherwise hard to produceand identify.Comment: 5 figures, 1 table, accepted for publication in Physical Review
Unveiling the intruder deformed 0 state in Si
The 0 state in Si has been populated at the {\sc Ganil/Lise3}
facility through the -decay of a newly discovered 1 isomer in
Al of 26(1) ms half-life. The simultaneous detection of pairs
allowed the determination of the excitation energy E(0)=2719(3) keV and
the half-life T=19.4(7) ns, from which an electric monopole strength of
(E0)=13.0(0.9) was deduced. The 2 state is
observed to decay both to the 0 ground state and to the newly observed
0 state (via a 607(2) keV transition) with a ratio
R(2)=1380(717). Gathering all
information, a weak mixing with the 0 and a large deformation parameter
of =0.29(4) are found for the 0 state, in good agreement with
shell model calculations using a new {\sc sdpf-u-mix} interaction allowing
\textit{np-nh} excitations across the N=20 shell gap.Comment: 5 pages, 3 figures, accepted for publication in Physical Review
Letter
Prolate-Spherical Shape Coexistence at N=28 in S
The structure of S has been studied using delayed and
electron spectroscopy at \textsc{ganil}. The decay rates of the 0
isomeric state to the 2 and 0 states have been measured for the
first time, leading to a reduced transition probability
B(E2~:~20= 8.4(26)~efm and a monopole
strength (E0~:~00
=~8.7(7)10. Comparisons to shell model calculations point
towards prolate-spherical shape coexistence and a phenomenological two level
mixing model is used to extract a weak mixing between the two configurations.Comment: 5 pages, 3 figures, accepted for publication in Physical Review
Letter
Spectroscopy of F
The structure of the weakly-bound F odd-odd nucleus,
produced from Na nuclei, has been investigated at GANIL by means of
the in-beam -ray spectroscopy technique. A single -line is
observed at 657(7) keV in F which has been ascribed to the decay of
the excited J= state to the J=1 ground state. The possible presence of
intruder negative parity states in F is also discussed.Comment: 3 pages, 1 figure, accepted for publication in Physical Review
Structure and Coulomb dissociation of 23O within the quark-meson coupling model
We study the ground-state structure of nuclei in the vicinity of the
one-neutron dripline within the latest version of the quark-meson coupling
(QMC) model with a particular emphasis on 23O. For this nucleus the model
predicts a [22O(0+) + n (2s_{1/2})] configuration for its ground state, with a
one neutron separation energy in close agreement with the corresponding
experimental value. The wave function describing the valence neutron-core
relative motion was then used to calculate the Coulomb dissociation of 23O on a
lead target at a beam energy of 422 MeV/nucleon. The experimental neutron-core
relative energy spectrum and the total one-neutron removal cross sections are
well described by the calculations. The widths of the longitudinal momentum
distributions of the 22O fragment are found to be broad, which do not support
the formation of a neutron halo in this nucleus.Comment: Revised and extended version, accepted for publication in Nucl. Phys.
New pathway to bypass the 15O waiting point
We propose the sequential reaction process
O(,)O as a new pathway to bypass of the
O waiting point. This exotic reaction is found to have a surprisingly
high cross section, approximately 10 times higher than the
O(,)O. These cross sections were calculated after
precise measurements of energies and widths of the proton-unbound F low
lying states, obtained using the H(O,p)O reaction. The large
cross section can be understood to arise from the more
efficient feeding of the low energy wing of the ground state resonance by the
gamma decay. The implications of the new reaction in novae explosions and X-ray
bursts are discussed.Comment: submitte
Collapse of the N=28 shell closure in Si
The energies of the excited states in very neutron-rich Si and
P have been measured using in-beam -ray spectroscopy from the
fragmentation of secondary beams of S at 39 A.MeV. The low 2
energy of Si, 770(19) keV, together with the level schemes of
P provide evidence for the disappearance of the Z=14 and N=28
spherical shell closures, which is ascribed mainly to the action of
proton-neutron tensor forces. New shell model calculations indicate that
Si is best described as a well deformed oblate rotor.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. let
Spectroscopy of the unbound nucleus 18Na
Expérience GANIL, SPIRALInternational audienceThe unbound nucleus 18Na, the intermediate nucleus in the two-proton radioactivity of 19Mg, is studied through the resonant elastic scattering 17Ne(p,17Ne)p. The spectroscopic information obtained in this experiment is discussed and put in perspective with previous measurements and the structure of the mirror nucleus 18N
\b{eta}-delayed three-proton decay of 31Ar
The beta decay of 31Ar, produced by fragmentation of a 36Ar beam at 880
MeV/nucleon, was investigated. Identified ions of 31Ar were stopped in a
gaseous time projection chamber with optical readout allowing to record decay
events with emission of protons. In addition to \b{eta}-delayed emission of one
and two protons we have clearly observed the beta-delayed three-proton branch.
The branching ratio for this channel in 31Ar is found to be 0.07(2)%.Comment: 5 pages, 3 figures, submitted to Physical Rev.
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