Beta-Gamma Angular Correlation Measurements onAu198. II. Transverse Polarization of the Beta Particles

Abstract

As a consequence of the nonconservation of parity in beta decay, beta particles emitted in first-forbidden beta transitions exhibit a small degree of polarization transverse to their momentum. The direction of the transverse polarization is defined with respect to a plane which is introduced by observing the direction of emission of the beta particle and the direction of emission of a gamma ray following the beta transition. The degree of the transverse polarization parallel to the beta-gamma plane $P_{T\mathrm{II}}$, and the degree of polarization perpendicular to the beta-gamma plane $P_{T\perp }$ has been measured for ${\mathrm{Au}}^{198}$. The beta polarization has been detected by means of the left-right asymmetry in a Mott scattering process for an average electron energy $W=2.0\mathrm{}$ ${\mathrm{mc}}^2$ and for an angle $\Theta =135\mathrm{}°$ between the beta momentum and the gamma direction. The results of the measurements, $P_{T\mathrm{II}}=+0.011\mathrm{}\pm 0.005$ and $P_{T\perp }=+0.03\mathrm{}\pm 0.008$, agree satisfactorily with the values calculated on the basis of the $\xi$ approximation from the anisotropy of the ${\mathrm{Au}}^{198}$ beta-gamma directional correlation.