390 research outputs found
Comment on "First Observation of Ground State Dineutron Decay: 16Be"
A recent measurement [Spyrou et al., PRL 108, 102501 (2012)] of the in-flight
decay of 16Be into 14Be+n+n has been interpreted as the first case of dineutron
emission. Here we point out that the inclusion of the n-n interaction neglected
in the description of the direct three-body decay can generate strong
enhancements at low n-n relative energy and angle, as observed, without any
need to invoke dineutron decay.Comment: Final version, published in Physical Review Letter
Structure of unbound neutron-rich He studied using single-neutron transfer
The 8He(d,p) reaction was studied in inverse kinematics at 15.4A MeV using
the MUST2 Si-CsI array in order to shed light on the level structure of 9He.
The well known 16O(d,p)17O reaction, performed here in reverse kinematics, was
used as a test to validate the experimental methods. The 9He missing mass
spectrum was deduced from the kinetic energies and emission angles of the
recoiling protons. Several structures were observed above the neutron-emission
threshold and the angular distributions were used to deduce the multipolarity
of the transitions. This work confirms that the ground state of 9He is located
very close to the neutron threshold of 8He and supports the occurrence of
parity inversion in 9He.Comment: Exp\'erience GANIL/SPIRAL1/MUST
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
The N = 16 spherical shell closure in 24O
The unbound excited states of the neutron drip-line isotope 24O have been
investigated via the 24O(p,p')23O+n reaction in inverse kinematics at a beam
energy of 62 MeV/nucleon. The decay energy spectrum of 24O* was reconstructed
from the momenta of 23O and the neutron. The spin-parity of the first excited
state, observed at Ex = 4.65 +/- 0.14 MeV, was determined to be Jpi = 2+ from
the angular distribution of the cross section. Higher lying states were also
observed. The quadrupole transition parameter beta2 of the 2+ state was
deduced, for the first time, to be 0.15 +/- 0.04. The relatively high
excitation energy and small beta2 value are indicative of the N = 16 shell
closure in 24O.Comment: to be submitted to Physical Review Letter
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
Modelling LAI at a regional scale with ISBA-A-gs: comparison with satellite-derived LAI over southwestern France
International audienceA CO2-responsive land surface model (the ISBAA- gs model of M´et´eo-France) is used to simulate photosynthesis and Leaf Area Index (LAI) in southwestern France for a 3-year period (2001–2003). A domain of about 170 000 km2 is covered at a spatial resolution of 8 km. The capability of ISBA-A-gs to reproduce the seasonal and the interannual variability of LAI at a regional scale, is assessed with satellite-derived LAI products. One originates from the CYCLOPES programme using SPOT/VEGETATION data, and two products are based on MODIS data. The comparison reveals discrepancies between the satellite LAI estimates and between satellite and simulated LAI values, both in their intensity and in the timing of the leaf onset. The model simulates higher LAI values for the C3 crops than the satellite observations, which may be due to a saturation effect within the satellite signal or to uncertainties in model parameters. The simulated leaf onset presents a significant delay for C3 crops and mountainous grasslands. In-situ observations at a mid-altitude grassland site show that the generic temperature response of photosynthesis used in the model is not appropriate for plants adapted to the cold climatic conditions of the mountainous areas. This study demonstrates the potential of LAI remote sensing products for identifying and locating models' shortcomings at a regional scale
Spectroscopy of 32Ne and the Island of Inversion
We report on the first spectroscopic study of the N=22 nucleus 32Ne at the
newly completed RIKEN Radioactive Ion Beam Factory. A single gamma-ray line
with an energy of 722(9) keV was observed in both inelastic scattering of a 226
MeV/u 32Ne beam on a Carbon target and proton removal from 33Na at 245 MeV/u.
This transition is assigned to the de-excitation of the first J^pi = 2+ state
in 32Ne to the 0+ ground state. Interpreted through comparison with
state-of-the-art shell model calculations, the low excitation energy
demonstrates that the Island of Inversion extends to at least N=22 for the Ne
isotopes.Comment: Accepted for publication in Phys. Rev. Lett. 11 pages, 3 figure
Recommended from our members
Mediterranean Sea response to climate change in an ensemble of twenty first century scenarios
The Mediterranean climate is expected to become warmer and drier during the twenty-first century. Mediterranean Sea response to climate change could be modulated by the choice of the socio-economic scenario as well as the choice of the boundary conditions mainly the Atlantic hydrography, the river runoff and the atmospheric fluxes. To assess and quantify the sensitivity of the Mediterranean Sea to the twenty-first century climate change, a set of numerical experiments was carried out with the regional ocean model NEMOMED8 set up for the Mediterranean Sea. The model is forced by air–sea fluxes derived from the regional climate model ARPEGE-Climate at a 50-km horizontal resolution. Historical simulations representing the climate of the period 1961–2000 were run to obtain a reference state. From this baseline, various sensitivity experiments were performed for the period 2001–2099, following different socio-economic scenarios based on the Special Report on Emissions Scenarios. For the A2 scenario, the main three boundary forcings (river runoff, near-Atlantic water hydrography and air–sea fluxes) were changed one by one to better identify the role of each forcing in the way the ocean responds to climate change. In two additional simulations (A1B, B1), the scenario is changed, allowing to quantify the socio-economic uncertainty. Our 6-member scenario simulations display a warming and saltening of the Mediterranean. For the 2070–2099 period compared to 1961–1990, the sea surface temperature anomalies range from +1.73 to +2.97 °C and the SSS anomalies spread from +0.48 to +0.89. In most of the cases, we found that the future Mediterranean thermohaline circulation (MTHC) tends to reach a situation similar to the eastern Mediterranean Transient. However, this response is varying depending on the chosen boundary conditions and socio-economic scenarios. Our numerical experiments suggest that the choice of the near-Atlantic surface water evolution, which is very uncertain in General Circulation Models, has the largest impact on the evolution of the Mediterranean water masses, followed by the choice of the socio-economic scenario. The choice of river runoff and atmospheric forcing both have a smaller impact. The state of the MTHC during the historical period is found to have a large influence on the transfer of surface anomalies toward depth. Besides, subsurface currents are substantially modified in the Ionian Sea and the Balearic region. Finally, the response of thermosteric sea level ranges from +34 to +49 cm (2070–2099 vs. 1961–1990), mainly depending on the Atlantic forcing
- …