Position sensitivity of segmented planar HPGe detectors for the DESPEC project at FAIR

One of the proposed germanium detector systems for the upcoming DESPEC array at the FAIR facility consists of triple modules of electrically segmented planar high-purity germanium detectors. In this work, the position sensitivity obtained by means of pulse shape analysis (PSA) for simulated γγ-ray interactions has been studied for the possible segmentation patterns for such detectors—the double-sided strip detector (DSSD) and the one-sided pixelated geometry. An over-all similar number of readout channels has been considered for each case, resulting in 8+88+8 strips and 16 pixels. It has been found that the higher physical granularity of the DSSD results in a significantly higher position resolution, as well as in a somewhat lower probability of merging multiple interaction points. A drawback of the DSSD geometry is the inability to assign the interactions to the correct voxels for certain complex multiple interaction patterns. This effect has been studied in detail. Finally, a comparison has been made with the existing 25-pixel planar detector at KTH [A. Khaplanov, et al., Nucl. Instr. and Meth. A 580 (2007) 1075; L. Milechina, B. Cederwall, Nucl. Instr. and Meth. A 550 (2005) 278)].