A method of measuring radioactivity emitted by a plurality of radionuclides using a source cage (100; 402) comprising an outer ring (102; 406) that defines a volume and a plurality of holes , wherein each hole of the plurality of holes is configured to receive a radionuclide of the plurality of radionuclides , and a frame (200; 408) comprising an arm coupled to a central rod (208; 412), wherein the central rod (208; 412) is coupled to a gamma detector (207; 414), wherein the outer ring (102; 406) comprises an orientation feature (107; 422), wherein the arm comprises an orientation pin configured to engage the orientation feature (107; 422), and wherein the central rod (208; 412) is configured to be positioned in a predetermined location relative to the volume when the orientation pin and the orientation feature (107; 422) are engaged, the method comprising: coupling the arm to the outer ring (102; 406) of the source cage (100; 402); arranging the arm and the central rod (208; 412) until the central rod is be positioned in the predetermined location relative to the volume ; engaging the orientation pin of the arm and the orientation feature (107; 422) of the outer ring (102; 406) of the source cage (100; 402); inserting a radionuclide of the plurality of radionuclides into a hole of the plurality of holes of the outer ring (102; 406) of the source cage (100; 402); taking a baseline measurement of radioactivity emitted by the inserted radionuclide using the gamma detector (207; 414); removing the radionuclide of the plurality of radionuclides from the hole of the plurality of holes of the outer ring (102; 406) of the source cage (100; 402); and inserting each radionuclide of the plurality of radionuclides into the plurality of holes of the outer ring (102; 406) of the source cage (100; 402); characterized by taking a collective measurement of radioactivity emitted by the plurality of radionuclides ; and dividing the collective measurement by the number of radionuclides of the plurality of radionuclides to determine an average measurement of radioactivity emitted by each radionuclide of the plurality of radionuclides . coupling the arm to the outer ring (102; 406) of the source cage (100; 402); arranging the arm and the central rod (208; 412) until the central rod is be positioned in the predetermined location relative to the volume ; engaging the orientation pin of the arm and the orientation feature (107; 422) of the outer ring (102; 406) of the source cage (100; 402); inserting a radionuclide of the plurality of radionuclides into a hole of the plurality of holes of the outer ring (102; 406) of the source cage (100; 402); taking a baseline measurement of radioactivity emitted by the inserted radionuclide using the gamma detector (207; 414); removing the radionuclide of the plurality of radionuclides from the hole of the plurality of holes of the outer ring (102; 406) of the source cage (100; 402); and inserting each radionuclide of the plurality of radionuclides into the plurality of holes of the outer ring (102; 406) of the source cage (100; 402); characterized by taking a collective measurement of radioactivity emitted by the plurality of radionuclides ; and dividing the collective measurement by the number of radionuclides of the plurality of radionuclides to determine an average measurement of radioactivity emitted by each radionuclide of the plurality of radionuclides . <EOS>