Transverse Polarization of theK-Conversion Electrons following the Beta Decay ofHg203

The transverse polarization of the $K$-conversion electrons following the $\beta$ decay of ${\mathrm{Hg}}^{203}$ has been investigated. A lens spectrometer was used to focus the conversion electrons on a Mott-scattering foil and the right-left asymmetry of the scattered conversion electrons in coincidence with the preceding $\beta$ particles was measured. A detailed discussion of the instrumental corrections is presented. The degree of transverse polarization of the ${\mathrm{Hg}}^{203}$ conversion electrons in the plane defined by the momenta ${\mathrm{p}}_{\beta }=m\mathrm{v}$ of the $\beta$ particles and ${\mathrm{p}}_c$ of the conversion electrons is described by $P_{\mathrm{II}}\left(\theta \right)=K\left(\frac{v}{c}\right)sin\theta$, where $\theta$ is the angle between ${\mathrm{p}}_{\beta }$ and ${\mathrm{p}}_c$. The experiments yielded the value of the polarization constant $K=+0.62\mathrm{}\pm 0.08$. The positive sign of $K$ implies that the spin of the conversion electrons is pointing in the same direction as the $\beta$-particle momentum ${\mathrm{p}}_{\beta }$. A comparison with the theory of Becker and Rose shows that the experimental value of $K$ is compatible with the spin assignments $I_i=\frac{1}{2}$ and $I_i=\frac{3}{2}$ to the ground state of ${\mathrm{Hg}}^{203}$. The spin $I_i=\frac{5}{2}$ is excluded. The most probable spin assignment is $I_i=\frac{3}{2}$, which gives good agreement with the observed polarization if the ratio $y^{\prime }$ of the scalar and the vector-type beta matrix elements is $y^{\prime }=-1.25\mathrm{}\pm 0.15$.