Elastic Electron Scattering from the Magnetic Multipole Distributions ofLi6,Li7,Be9,B10,B11andN14

Abstract

The magnetic form factors of the $1p$-shell nuclei ${\mathrm{Li}}^{6}$, ${\mathrm{Li}}^{7}$, ${\mathrm{Be}}^{9}$, ${\mathrm{B}}^{10}$, ${\mathrm{B}}^{11}$, ${\mathrm{N}}^{14}$, have been measured by high-energy electron scattering at an angle of 180\ifmmode^\circ\else\textdegree\fi{}. Incident electron energies up to 230 MeV (${q}^{2}\ensuremath{\simeq}5.2$ ${\mathrm{F}}^{\ensuremath{-}2}$) were used. The incident- and scattered-electron paths were separated by use of a uniform magnetic field. Back-ground due to charge scattering was subtracted by varying the scattering angle around 180\ifmmode^\circ\else\textdegree\fi{}. At the higher momentum transfers the scattering from those nuclei having spin $\ensuremath{\ge}\frac{3}{2}$, was dominated by the octupole moment distributions. Results are interpreted in terms of harmonic-oscillator and finite-square-well shell models. Parameters dependent only on the coupling of the angular momenta in the $1p$ shell may be obtained from the data. They show a general trend from $L\ensuremath{-}S$ coupling to $j\ensuremath{-}j$ coupling as the mass number increases, in agreement with calculations of magnetic dipole moments and energy-level schemes. The outstanding exception is ${\mathrm{Li}}^{7}$, whose form factor is accurately described by the extreme independent-particle model. ($L\ensuremath{-}S$ coupling is quite incompatible with the data.) The ${\mathrm{Li}}^{6}$ results may also be interpreted in terms of an alpha plus deuteron model. Numerical results for the harmonic-well strengths are obtained and compare favorably with electron-charge-scattering values. It is also possible to estimate magnetic octupole moments, where applicable, with fair accuracy, although these estimations are to a certain extent model-dependent.