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

M. Aliotta; C. Spitaleri; M. Lattuada; A. Musumarra; R.G. Pizzone; A. Tumino; C. Rolfs; F. Strieder

doi:doi:10.1007/s100500070001

2021 Impact factor 3.131

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 S_b(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 S_s(E)factor. The comparison between S_b(E) and S_s(E)leads to an electron-screening potential energy U_e=350eV, which is much higher than the adiabatic limit of 175eV and not understood at present. The deduced value of S_b(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 S_b(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 S_b(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.