A γ-ray polarimeter based on a single segmented planar HPGe detector

The polarization sensitivity of a segmented planar HPGe detector has been measured. For this purpose 662 keV photons from a ¹³⁷Cs source which were Compton scattered at ≈ 90^{{ring operator}} in a coaxial germanium detector were utilized as a source of partially linearly polarized gamma radiation of the energy ≈ 288 keV. The detector has a 50 × 50 × 21 mm sensitive volume and 5 × 5 electrical segmentation of the cathode contact. The degree of linear polarization is determined through the analysis of the directions of Compton scatterings inside the detector. The locations of the Compton scattering interactions and of the subsequent photo-absorption interactions have been determined with the help of pulse shape analysis (PSA), provided that these interactions are in two different segments of the planar detector. A comparison with a polarization analysis using the position resolution defined by the physical segmentation (without the use of PSA) was also performed. It is demonstrated that the use of PSA enables a much higher polarization sensitivity for events where the 288 keV photons scatter between adjacent pixels. Such events constitute 90% of the data for the 288 keV photons and are even more important for γ-rays of lower energies.