Elastic Electron Scattering fromLi6andLi7

Abstract

The nuclear-charge form factors for elastic electron scattering on ${\mathrm{Li}}^6$ and ${\mathrm{Li}}^7$ have been determined from measurements at primary beam energies of 100 to 600 MeV. The maximum square of the momentum transferred to the nuclei was 6.9 ${\mathrm{F}}^{-2\mathrm{}}$. Absolute values of the cross sections were obtained by comparison with the known absolute proton cross section. For measurements at the primary-beam energy of 100 MeV, however, only the ratio of the ${\mathrm{Li}}^7$ cross section to the ${\mathrm{Li}}^6$ cross section was measured. The charge form factor for ${\mathrm{Li}}^7$ could be interpreted in terms of a simple harmonic-oscillator shell model with a quadrupole contribution described by the underformed $p$-shell model. For this model, the rms charge radius was 2.39±0.03 F, and the electric-quadrupole moment required for the fit was in excellent agreement with the spectroscopic measurements. The ${\mathrm{Li}}^6$ charge form factor could not be interpreted either in terms of the simple harmonic-well shell model, or in terms of the modified harmonic-well model in which the $s$ and $p$ nucleons are permitted to move in potential wells of different strengths. The rms radius obtained for a phenomenological fit to the data was 2.54±0.05 F. The ratio of the ${\mathrm{Li}}^6$ and ${\mathrm{Li}}^7$ rms radii, as determined from the 100-MeV measurements, was 1.055±0.008. This is in agreement with the ratio as determined from the best-fit form factors which were obtained from the complete range in $q^2$ of the data.