2018 Impact factor 2.481
Hadrons and Nuclei

Eur. Phys. J. A 9, 435-437

Short Note

Improved information on electron screening in \ensuremath{\mathsf{^{7}Li}} $\bf {(p,\alpha)\alpha}$ using the Trojan-horse method

M. Aliotta1 - C. Spitaleri2 - M. Lattuada2 - A. Musumarra2 - R.G. Pizzone2 - A. Tumino3 - C. Rolfs1 - F. Strieder1

1 Institut für Physik mit Ionenstrahlen, Ruhr-Universität Bochum, Germany
2 Dipartimento di Metodologie Fisiche e Chimiche per l'Ingegneria dell'Università di Catania and INFN - Laboratori Nazionali del Sud, Catania, Italy
3 Dipartimento di Fisica e Astronomia dell'Università di Catania and INFN - Laboratori Nazionali del Sud, Catania, Italy

Received: 9 September 2000 / Revised version: 14 November 2000
Communicated by J. Äystö

Abstract
The available astrophysical S(E) factor data for the reaction \ensuremath{\mathsf{^{7}Li}} $(p,\alpha)\alpha$ at 10<E<1000keV exhibit an exponential increase at low energies due to the effects of electron screening. A parametrisation of the data using a non-resonant, direct process and two subthreshold resonances reproduces the data at energies $E\geq100$keV, while at lower energies this calculated Sb(E) factor curve for bare nuclides drops below the data, which in turn represent the case of electron-shielded nuclides, i.e. the electron-shielded Ss(E)factor. The comparison between Sb(E) and Ss(E)leads to an electron-screening potential energy Ue=350eV, which is much higher than the adiabatic limit of 175eV and not understood at present. The deduced value of Sb(0) is considerably smaller than the previously adopted value of 59keV b, significantly increasing the calculated abundance of \ensuremath{\mathsf{^{7}Li}} in big-bang nucleosynthesis. The Trojan-horse method was applied to the reaction \ensuremath{\mathsf{^{7}Li}} $(p,\alpha)\alpha$ to determine the energy dependence of the Sb(E) factor for 10<E<370keV, free from the effects of the Coulomb barrier and electron screening. The THM results are close to the calculated Sb(E) curve and suggest that the THM may become a powerful way to obtain improved information on low-energy cross-sections and associated electron-screening effects in a model-independent way.

PACS
24.10.-i Nuclear-reaction models and methods - 25.40.-h Nucleon-induced reactions - 26.35.+c Big bang nucleosynthesis


Copyright Società Italiana di Fisica, Springer-Verlag 2000