28 research outputs found
First direct observation of two protons in the decay of Fe with a TPC
The decay of the ground-state two-proton emitter 45Fe was studied with a
time-projection chamber and the emission of two protons was unambiguously
identified. The total decay energy and the half-life measured in this work
agree with the results from previous experiments. The present result
constitutes the first direct observation of the individual protons in the
two-proton decay of a long-lived ground-state emitter. In parallel, we
identified for the first time directly two-proton emission from 43Cr, a known
beta-delayed two-proton emitter. The technique developped in the present work
opens the way to a detailed study of the mechanism of ground-state as well as
beta-delayed two-proton radioactivity.Comment: 4 pages, 5 figure
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
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
Spectroscopy around Ca
Expérience GANILInternational audienceAn experiment was performed to study excited states in neutron-deficient nuclei around Ca. A one-neutron knockout reaction was used to produce Ca ions from a Ca secondary beam, and in-beam -rays were measured. The energy in Ca is compared to the mirror nucleus S to deduce information on the isospin dependence of the nuclear force near the proton drip line. The energy of the first excited state in Ca and the cross section for the 1-neutron knock-out reaction from Ca at 45 · AMeV were obtained. Furthermore, for two other = −2 nuclei, S and Ar, the de-excitation of the first state has been observed
In-beam spectroscopic studies of S nucleus
The structure of the S nucleus has been studied at GANIL through the
one proton knock-out reaction from a Cl secondary beam at 42
AMeV. The rays following the de-excitation of S were
detected in flight using the 70 BaF detectors of the Ch\^{a}teau de
Cristal array. An exhaustive -coincidence analysis allowed an
unambiguous construction of the level scheme up to an excitation energy of 3301
keV. The existence of the spherical 2 state is confirmed and three new
-ray transitions connecting the prolate deformed 2 level were
observed. Comparison of the experimental results to shell model calculations
further supports a prolate and spherical shape coexistence with a large mixing
of states built on the ground state band in S.Comment: 6 pages, 5 figures, accepted for publication in Physical Review
Measurements of nuclear -ray line emission in interactions of protons and particles with N, O, Ne and Si.
42 pages, 12 figures, 7 tables, submitted to Phys. Rev. CInternational audience-ray production cross sections have been measured in proton irradiations of N, Ne and Si and -particle irradiations of N and Ne. In the same experiment we extracted also line shapes for strong -ray lines of O produced in proton and -particle irradiations of O. For the measurements gas targets were used for N, O and Ne and a thick foil was used for Si. All targets were of natural isotopic composition. Beams in the energy range up to 26 MeV for protons and 39 MeV for -particles have been delivered by the IPN-Orsay tandem accelerator. The rays have been detected with four HP-Ge detectors in the angular range 30 to 135. We extracted 36 cross section excitation functions for proton reactions and 14 for -particle reactions. For the majority of the excitation functions no other data exist to our knowledge. Where comparison with existing data was possible usually a very good agreement was found. It is shown that these data are very interesting for constraining nuclear reaction models. In particular the agreement of cross section calculations in the nuclear reaction code TALYS with the measured data could be improved by adjusting the coupling schemes of collective levels in the target nuclei N, Ne and Si. The importance of these results for the modeling of nuclear -ray line emission in astrophysical sites is discussed
Discovery of a New Broad Resonance in Ne-19: Implications for the Destruction of the Cosmic gamma-Ray Emitter F-18
The experiment was performed at the Centre de Recherches du Cyclotron at Louvain-la-Neuve (Belgium) using a 19Ne6+ radioactive beam.International audienceSix proton-emitting states in 19Ne were studied through the inelastic scattering reaction H(19Ne; p)19Ne*(p)18F. Their energies and widths were derived from the protons detected at zero degree, while proton-proton angular correlations between the detector at zero degree and a segmented annular detector were used to determine their spin value. Besides the known states, a new broad J = 1/2 resonance has been evidenced at Ex ≈ 7.9 MeV, ≈ 1:45 MeV above the proton emission threshold. By introducing this resonance, the 18F(p; alpha)15O destruction rate in novae is significantly enhanced. This reduces the chance to observe the cosmic gamma-ray emission of 18F from novae in space telescopes
Quasi-bound low energy tail of resonance
International audienceGround states of particle-unbound nuclei are seen as resonances. According to the Heisenberg's uncertainty principle, the shorter is the lifetime of the state the broader is the resonance. The Breit-Wigner function describes perfectly the shape of the resonance when energy-dependent partialwidths are used. In the low energy tail of a resonance, close to the particle-emission threshold, the partial-width for the emission of a charged particle through the Coulomb barrier is dramatically reduced. In this region of the resonance, the charged particle could be trapped inside the unboundnucleus. This idea will be discussed in more details and experimental aspects will be given