Measurement of the Mobility of Positrons in Germanium

The mobility ${\mu }_{+}$ of positrons in Ge has been measured. Energetic positrons from a radioactive source enter an intrinsic planar Ge detector where they annihilate in the presence of the detector bias field. The motion of the positrons is detected by observing the Doppler shift of the annihilation $\gamma \text{'}\mathrm{s}$ as a function of the voltage across the detector. We obtain ${\mu }_{+}=(124\mathrm{}\pm 10)$ ${\mathrm{cm}}^2$ ${\mathrm{V}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ at (93±5) K and ${\mu }_{+}=(350\mathrm{}\pm 17)$ ${\mathrm{cm}}^2$ ${\mathrm{V}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ at (36±5) K.