Uncertainties in the ground state structure of 8B and implications for the S17 astrophysical S-factor

doi:10.1016/S0375-9474(96)00466-6

Nuclear Physics A

Volume 615, Issue 1, 17 March 1997, Pages 69-81

https://doi.org/10.1016/S0375-9474(96)00466-6 Get rights and content

Abstract

In calculating the ⁷Be(p,γ)⁸B reaction rate, various single particle models have been used to describe the g.s. of ⁸B. We show that these models produce electric excitation strength distributions that can differ greatly (⋍ 30%) from the pioneering model, providing the community with a wide range of values for the low energy S-factor, even if no other differences in the reaction theory are introduced. When allowing for deformation of the ⁷Be core, the maximum of the dB(E1)/dE distribution can be reduced by (⋍ 15%) and the peak shifts slightly to higher energies. The change in the B(E1) distribution modifies the low energy behaviour of the astrophysical S-factor and brings a reduction of its overall magnitude.

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2002, Nuclear Physics A
We propose a general method to test the uniqueness property of the Asymptotic Normalization Constant, ANC. We apply this method for the case of the vertex ¹⁰B → ⁹Be+p using a set of different proton-transfer reactions at different energies. Given the limited sets of data for peripheral transfer reactions, we underline the present difficulties in extracting astrophysical S-factors and point out the inadequacy of some of the available data. Finally, we make some suggestions for future experiments in order to make this test conclusive.
Structure effects on the Coulomb dissociation of 8B at relativistic energies
2000, Nuclear Physics A
We investigate the Coulomb dissociation of $^{8}$ B on a $^{208}$ Pb target at the beam energy of 250 MeV/nucleon, employing the cross sections for the radiative capture reaction $^{7}$ Be(p,γ) $^{8}$ B calculated within the Shell Model Embedded in the Continuum (SMEC) approach. In contrast to the situation at lower beam energies, the Coulomb breakup cross sections are found to be sensitive to the M1 transitions. Comparisons of SMEC and single-particle potential model predictions show that the Coulomb breakup cross sections at these high energies are sensitive to the structure model of $^{8}$ B. Comparison with the preliminary data on the angle integrated spectra reported recently by the GSI group shows that the theory is able to reproduce the absolute magnitude as well as the shape of this data well. The contributions of the E2 component strongly depends on the range of the angles of the p– $^{7} Be$ center of mass with respect to the beam direction, included in the angular integrations of the double differential cross section. If integrations are done over the angular range of 0°–1.87°, the E2 multipolarity contributes up to 25 % to the cross sections even for the relative energies of [p– $^{7} Be$ ] below 0.25 MeV. However, these contributions are reduced by an order of magnitude at lower relative energies if the maximum of the angle integration is ∼ 1°.
Study of the 7Be(p, γ)8B and 7Li(n, γ)8Li capture reactions using the shell model embedded in the continuum
1999, Nuclear Physics A
The solar neutrino problem - An update
1999, Physics Report
The ⁸B solar neutrino flux that has recently been measured by Super-Kamiokande is consistent with the ³⁷Ar production rate in ³⁷Cl at Homestake. The gallium solar neutrino experiments, GALLEX and SAGE, continue to observe ⁷¹Ge production rates in ⁷¹Ga that are consistent with the minimal signal expected from the solar luminosity. The observed ⁸B solar neutrino flux is in good agreement with that predicted by the standard solar model of Dar and Shaviv with nuclear reaction rates that are supported by recent measurements of nuclear fusion cross sections at low energies. But, the signals measured by Super-Kamiokande, SAGE and GALLEX leave no room for the contribution from the expected ⁷Be solar neutrino flux. This apparent suppression of the ⁷Be solar neutrino flux can be explained by neutrino oscillations and the Mikheyev–Smirnov–Wolfenstein effect, although neither a flavor change, nor a terrestrial variation, nor a spectral distortion of the ⁸B solar neutrino flux has been observed. Detailed helioseismology data from SOHO and GONG confirm the standard solar model description of the solar core, but helioseismology is insensitive to the fate of ⁷Be in the sun and the production rates of ⁷Be, CNO and ⁸B neutrinos. Thus, helioseismology and the solar neutrino problem do not provide conclusive evidence for neutrino properties beyond the standard electroweak model. The solar neutrino problem may still be an astrophysical problem. The deviations of the experimental results from those predicted by the standard solar models may reflect the approximate nature of our knowledge of nuclear reaction rates and radiation transport in dense stellar plasmas and the approximate nature of solar models. Only future observations of spectral distortions, or terrestrial modulation or flavor change of solar neutrinos in solar neutrino experiments, such as Super-Kamiokande, SNO, Borexino and HELLAZ will be able to establish that neutrino properties beyond the minimal standard electroweak model are responsible for the solar neutrino problem.
E2 component in subcoulomb breakup of 8B 1
1997, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
We calculate the angular distribution and total cross section of the ⁷Be fragment emitted in the break up reaction of ⁸B on ⁵⁸Ni and ²⁰⁸Pb targets at the subcoulomb beam energy of 25.8 MeV, within the non-relativistic theory of Coulomb excitation with proper three-body kinematics. The relative contributions of the E1, E2 and M1 multipolarities to the cross sections are determined. The E2 component makes up about 65% and 40% of the ⁷Be total cross section for the ⁵⁸Ni and ²⁰⁸Pb targets respectively. We find that the extraction of the astrophysical S-factor, S₁₇(0), for the ⁷Be(p,γ)⁸B reaction at solar energies from the measurements of the cross sections of the ⁷Be fragment in the Coulomb dissociation of ⁸B at sub-Coulomb energies is still not free from the uncertainties of the E2 component.

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Nuclear Physics A

Abstract

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Cited by (24)

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Structure effects on the Coulomb dissociation of <sup>8</sup>B at relativistic energies

Study of the <sup>7</sup>Be(p, γ)<sup>8</sup>B and <sup>7</sup>Li(n, γ)<sup>8</sup>Li capture reactions using the shell model embedded in the continuum

The solar neutrino problem - An update

E2 component in subcoulomb breakup of <sup>8</sup>B <sup>1</sup>