Measurement of the Circular Polarization of Resonance-Scattered Gamma Rays Following the Electron Capture ofSe75

The circular polarization of the 265-kev $\gamma$ rays following the mixed Gamow-Teller and Fermi electron-capture decay of ${\mathrm{Se}}^{75}$ into ${\mathrm{As}}^{75}$ has been measured. The neutrino momentum was fixed with the help of a resonance scattering process. From the experimentally determined degree of right-hand circular polarization of -0.21±0.15 it was concluded that the sign of the Gamow-Teller to Fermi matrix-element ratio in this beta decay is negative.