Experimental position resolution of the segmented inverted-coaxial germanium detector, SIGMA

The Segmented Inverted-coaxial GerMAnium (SIGMA) detector is a large-volume, position-sensitive high-purity germanium detector developed for γ -ray tracking and imaging. The SIGMA detector features an inverted-coaxial geometry with a unique configuration of 18 segments providing position sensitivity, complemented by small point-contact technology for excellent energy resolution. In this work, the position resolution of SIGMA has been experimentally evaluated using pulse shape analysis with a simulated signal database generated using the AGATA Detector Library. The simulated response was validated against experimental signals and optimised through variation of the detector impurity concentration and charge-carrier mobility parameters. At 662 keV, the radial position resolution was found to be 2.8 mm in the outer-segment region and 4.1 mm in the core region, with an azimuthal resolution of approximately 7° and a position resolution through depth along the crystal length of 2.4 mm. After correcting for the contributions from the finite γ -ray beam width and the granularity of the database, the intrinsic resolution was found to be 2.5 mm (outer) and 3.9 mm (core) radially, 6.5° azimuthally, and 2.0 mm through depth. The resulting intrinsic three-dimensional resolution was determined to be 3.8 mm in the outer-segment region and 4.5 mm in the core region, consistent with previous simulation predictions for standalone operation of the detector. These results represent the first experimental position resolution measurements for the SIGMA detector.