226 research outputs found
Spectroscopy of Ne for the thermonuclear O()Ne and F()O reaction rates
Uncertainties in the thermonuclear rates of the
O()Ne and F()O reactions
affect model predictions of light curves from type I X-ray bursts and the
amount of the observable radioisotope F produced in classical novae,
respectively. To address these uncertainties, we have studied the nuclear
structure of Ne over MeV and MeV using
the F(He,t)Ne reaction. We find the values of the
4.14 and 4.20 MeV levels to be consistent with and
respectively, in contrast to previous assumptions. We confirm the recently
observed triplet of states around 6.4 MeV, and find evidence that the state at
6.29 MeV, just below the proton threshold, is either broad or a doublet. Our
data also suggest that predicted but yet unobserved levels may exist near the
6.86 MeV state. Higher resolution experiments are urgently needed to further
clarify the structure of Ne around the proton threshold before a
reliable F()O rate for nova models can be determined.Comment: 5 pages, 3 figures, Phys. Rev. C (in press
Status of the Standard Solar Model Prediction of Solar Neutrino Fluxes
The Standard Solar Model (BP04) predicts a total 8B neutrino flux that is
17.2% larger than measured in the salt phase of the SNO detector (and if it
were significant it will indicate oscillation to sterile neutrinos). Hence it
is important to examine in details uncertainties (and values) of inputs to the
SSM. Currently, the largest fractional uncertainty is due to the new evaluation
of the surface composition of the sun. We examine the nuclear input on the
formation of solar 8B [S17(0)] and demonstrate that it is still quite uncertain
due to ill known slope of the measured astrophysical cross section factor and
thus ill defined extrapolation to zero energy. This yields an additional
reasonably estimated uncertainty due to extrapolation of +0.0 -3.0 eV-b (+0%
-14%). Since a large discrepancy exists among measured as well as among
predicted slopes, the value of S17(0) is dependent on the choice of data and
theory used to extrapolate S17(0). This situation must be alleviated by new
measurement(s). The "world average" is driven by the Seattle result due to the
very small quoted uncertainty, which we however demonstrate it to be an
over-estimated accuracy. We propose more realistic error bars for the Seattle
results based on the published Seattle data.Comment: Fifth International Conferenceon Non-Accelerator New Physics, Dubna,
June 20-25, 2005. Work Supported by USDOE Grant No. DE-FG02-94ER4087
Low-energy cross section of the 7Be(p,g)8B solar fusion reaction from Coulomb dissociation of 8B
Final results from an exclusive measurement of the Coulomb breakup of 8B into
7Be+p at 254 A MeV are reported. Energy-differential Coulomb-breakup cross
sections are analyzed using a potential model of 8B and first-order
perturbation theory. The deduced astrophysical S_17 factors are in good
agreement with the most recent direct 7Be(p,gamma)8B measurements and follow
closely the energy dependence predicted by the cluster-model description of 8B
by Descouvemont. We extract a zero-energy S_17 factor of 20.6 +- 0.8 (stat) +-
1.2 (syst) eV b.Comment: 14 pages including 16 figures, LaTeX, accepted for publication in
Physical Review C. Minor changes in text and layou
First application of the Trojan Horse Method with a Radioactive Ion Beam: study of the F()O}} reaction at astrophysical energies
Measurement of nuclear cross sections at astrophysical energies involving
unstable species is one of the most challenging tasks in experimental nuclear
physics. The use of indirect methods is often unavoidable in this scenario. In
this paper the Trojan Horse Method is applied for the first time to a
radioactive ion beam induced reaction studying the
F()O process at low energies relevant to astrophysics
via the three body reaction H(F,O)n. The knowledge
of the F()O reaction rate is crucial to understand
the nova explosion phenomena. The cross section of this reaction is
characterized by the presence of several resonances in Ne and possibly
interference effects among them. The results reported in Literature are not
satisfactory and new investigations of the F()O
reaction cross section will be useful. In the present work the spin-parity
assignments of relevant levels have been discussed and the astrophysical
S-factor has been extracted considering also interference effectsComment: 7 pages, 4 figure
Region of hadron-quark mixed phase in hybrid stars
Hadron--quark mixed phase is expected in a wide region of the inner structure
of hybrid stars. However, we show that the hadron--quark mixed phase should be
restricted to a narrower region to because of the charge screening effect. The
narrow region of the mixed phase seems to explain physical phenomena of neutron
stars such as the strong magnetic field and glitch phenomena, and it would give
a new cooling curve for the neutron star.Comment: to be published in Physical Review
Low energy measurement of the 7Be(p,gamma)8B cross section
We have measured the cross section of the 7Be(p,gamma)8B reaction for E_cm =
185.8 keV, 134.7 keV and 111.7 keV using a radioactive 7Be target (132 mCi).
Single and coincidence spectra of beta^+ and alpha particles from 8B and 8Be^*
decay, respectively, were measured using a large acceptance spectrometer. The
zero energy S factor inferred from these data is 18.5 +/- 2.4 eV b and a
weighted mean value of 18.8 +/- 1.7 eV b (theoretical uncertainty included) is
deduced when combining this value with our previous results at higher energies.Comment: Accepted for publication in Phys. Rev. Let
Asymptotic normalization coefficient of ^{8}B from breakup reactions and the S_{17} astrophysical factor
We show that asymptotic normalization coefficients (ANC) can be extracted
from one nucleon breakup reactions of loosely bound nuclei at 30-300 MeV/u. In
particular, the breakup of ^{8}B is described in terms of an extended Glauber
model. The 8B ANC extracted for the ground state of this nucleus from breakup
data at several energies and on different targets, C^2 = 0.450+/-0.039} fm^-1,
leads to the astrophysical factor S_{17}(0)= 17.4+/-1.5 eVb for the key
reaction for solar neutrino production 7Be(p,gamma)8B. The procedure described
here is more general, providing an indirect method to determine reaction rates
of astrophysical interest with beams of loosely bound radioactive nuclei.Comment: 4 pages, RevTex, 3 figures revised version to appear in Phys Rev Let
Radiative capture and electromagnetic dissociation involving loosely bound nuclei: the B example
Electromagnetic processes in loosely bound nuclei are investigated using an
analytical model. In particular, electromagnetic dissociation of B is
studied and the results of our analytical model are compared to numerical
calculations based on a three-body picture of the B bound state. The
calculation of energy spectra is shown to be strongly model dependent. This is
demonstrated by investigating the sensitivity to the rms intercluster distance,
the few-body behavior, and the effects of final state interaction. In contrast,
the fraction of the energy spectrum which can be attributed to E1 transitions
is found to be almost model independent at small relative energies. This
finding is of great importance for astrophysical applications as it provides us
with a new tool to extract the E1 component from measured energy spectra. An
additional, and independent, method is also proposed as it is demonstrated how
two sets of experimental data, obtained with different beam energy and/or
minimum impact parameter, can be used to extract the E1 component.Comment: Submitted to Phys. Rev. C. 10 pages, 7 figure
Measurement of E2 Transitions in the Coulomb Dissociation of 8B
In an effort to understand the implications of Coulomb dissociation
experiments for the determination of the 7Be(p,gamma)8B reaction rate,
longitudinal momentum distributions of 7Be fragments produced in the Coulomb
dissociation of 44 and 81 MeV/nucleon 8B beams on a Pb target were measured.
These distributions are characterized by asymmetries interpreted as the result
of interference between E1 and E2 transition amplitudes in the Coulomb breakup.
At the lower beam energy, both the asymmetries and the measured cross sections
are well reproduced by perturbation theory calculations, allowing a
determination of the E2 strength.Comment: 8 pages, 3 figure
Gamma ray production cross sections in proton induced reactions on natural Mg, Si and Fe targets over the proton energy range 30 up to 66 MeV
Gamma-ray excitation functions have been measured for 30, 42, 54 and 66 MeV
proton beams accelerated onto C + O (Mylar), Mg, Si, and Fe targets of
astrophysical interest at the separate-sector cyclotron of iThemba LABS in
Somerset West (Cape Town, South Africa). A large solid angle, high energy
resolution detection system of the Eurogam type was used to record Gamma-ray
energy spectra. Derived preliminary results of Gamma-ray line production cross
sections for the Mg, Si and Fe target nuclei are reported and discussed. The
current cross section data for known, intense Gamma-ray lines from these nuclei
consistently extend to higher proton energies previous experimental data
measured up to Ep ~ 25 MeV at the Orsay and Washington tandem accelerators.
Data for new Gamma-ray lines observed for the first time in this work are also
reported.Comment: 11 pages, 6 figures. IOP Institute of Physics Conference Nuclear
Physics in Astrophysics VII, 28th EPF Nuclear Physics Divisional Conference,
May 18-22 2015, York, U
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