A device configured to measure radioactivity emitted by a plurality of radionuclides is disclosed herein. The device includes a gamma detector and a source cage with an outer ring that defines a volume and includes an orientation feature and a plurality of holes configured to receive a radionuclide of the plurality of radionuclides. The device also includes a frame that includes an arm and a central rod, wherein the arm is configured to be coupled to the outer ring and includes an orientation pin. The central rod can be positioned relative to the volume when the arm is coupled to the outer ring of source cage. The orientation feature of the source cage is configured to engage the orientation pin of the arm and, when the orientation pin engages the orientation feature, the central rod is in a predetermined location relative to the volume.