1,096 research outputs found
Microscopic calculations for solar nuclear reactions
We have studied the 4He(3He,gamma)7Be, 3He(3He,2p)4He, and 7Be(p,gamma)8B
reactions of the solar p-p chain, using microscopic cluster models. Among other
results, we showed that the 6Li+p channel has a nontrivial effect on the
7Be-producing reaction, that the existence of a resonance in 6Be close to the
3He+3He threshold is rather unlikely, and that the correlations between some
properties of 7Be/8B and the low-energy cross section of 7Be(p,gamma)8B might
help one to constrain the value of the S_17(0) astrophysical S-factor.Comment: 3 pages with 1 figure. Proceedings of the Nuclei in the Cosmos
Conference, Aarhus, Denmark, June 27-July 1, 2000. To be published in Nuclear
Physics A. The postscript file and more information are available at
http://matrix.elte.hu/~csoto and http://www.dfi.aau.dk/~langanke
Towards Microscopic Ab Initio Calculations of Astrophysical S-Factors
Low energy capture cross sections are calculated within a microscopic
many-body approach using an effective Hamiltonian derived from the Argonne V18
potential. The dynamics is treated within Fermionic Molecular Dynamics (FMD)
which uses a Gaussian wave-packet basis to represent the many-body states. A
phase-shift equivalent effective interaction derived within the Unitary
Correlation Operator Method (UCOM) that treats explicitly short-range central
and tensor correlations is employed. As a first application the
3He(alpha,gamma)7Be reaction is presented. Within the FMD approach the
microscopic many-body wave functions of the 3/2- and 1/2- bound states in 7Be
as well as the many-body scattering states in the 1/2+, 3/2+ and 5/2+ channels
are calculated as eigenstates of the same microscopic effective Hamiltonian.
Finally the S-factor is calculated from E1 transition matrix elements between
the many-body scattering and bound states. For 3He(alpha,gamma)7Be the S-factor
agrees very well, both in absolute normalization and energy dependence, with
the recent experimental data from the Weizmann, LUNA, Seattle and ERNA
experiments. For the 3H(alpha,gamma)7Li reaction the calculated S-factor is
about 15% above the data
Weak reactions on 12C within the Continuum Random Phase Approximation with partial occupancies
We extend our previous studies of the neutrino-induced reactions on 12C and
muon capture to include partial occupation of nuclear subshells in the
framework of the continuum random phase approximation. We find, in contrast to
the work by Auerbach et al., that a partial occupation of the p1/2 subshell
reduces the inclusive cross sections only slightly. The extended model
describes the muon capture rate and the 12C(nu_e,e-)12N cross section very
well. The recently updated flux and the improved model bring the calculated
12C(nu_mu,mu^-)12N cross section (~ 17.5 10^{-40} cm^2) and the data (12.4 +/-
0.3(stat.) +/- 1.8(syst.) 10^{-40} cm^2) closer together, but does not remove
the discrepancy fully.Comment: 12 pages, 2 figure
Estimates of weak and electromagnetic nuclear decay signatures for neutrino reactions in Super-Kamiokande
We estimate possible delayed β decay signatures of the neutrino induced reactions on 16O in a two-step model: the primary neutrino (ν,l) process, where l is the lepton in the final state, is described within the random phase approximation, while the subsequent decay of the excited nuclear state in the final channel is treated within the statistical model. We calculate partial reaction cross sections leading to β unstable nuclei. We consider neutrino energies up to 500 MeV, relevant for atmospheric neutrino detection in Super-Kamiokande, and supernova neutrino spectra
Muon capture on nuclei: random phase approximation evaluation versus data for 6 Z 94 nuclei
We use the random phase approximation to systematically describe the total
muon capture rates on all nuclei where they have been measured. We reproduce
the experimental values on these nuclei to better than 15% accuracy using the
free nucleon weak form factors and residual interactions with a mild
dependency. The isospin dependence and the effects associated with shell
closures are fairly well reproduced as well. However, the calculated rates for
the same residual interactions would be significantly lower than the data if
the in-medium quenching of the axial-vector coupling constant is employed to
other than the true Gamow-Teller amplitudes. Our calculation thus suggests that
no quenching is needed in the description of semileptonic weak processes
involving higher multipole transitions and momentum transfer ,
with obvious importance to analogous weak processes.Comment: RevTeX4 10 pages, 2 figures. Revised according to referee report.
Table 1 expanded. Accepted for publication in PR
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