Spin and Parity ofF20Levels from Gamma-Ray Linear-Polarization Measurements

The status of experimental quantum number assignments to low-lying levels of ${}_{}{}^{20}{}_{}{}^{}\mathrm{F}$ is reviewed. The use of a Compton-scattering polarimeter of limited resolution but good efficiency, in coincidence with an annular particle detector and perpendicular to the reaction symmetry axis, is described. Measurements of ${}_{}{}^{20}{}_{}{}^{}{\mathrm{F}}^{*}\mathrm{deexcitation}$ $\gamma$-ray polarization have been carried out following the ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}({}_{}{}^3{}_{}{}^{}\mathrm{He},p)$ reaction at 3.8 MeV and 0°. In conjunction with past experiments, the following assignments are inferred: 656 keV, $3^{+}$; 823 keV, $4^{+}$; 984 keV, $1^{-}$; 1309 keV, $2^{-}$; 1824 keV, $5^{+}$; and 1843 keV, ($2^{-}$). The relation of the experimental level structure to the rotational band grouping and to the $\mathrm{pds}$ shell-model calculation of McGrory and and Wildenthal is illustrated.