Abstract
Accurate and efficient secondary calibration of radionuclides remains a challenge in radionuclide metrology, with limited guidance on optimizing operational parameters for 4π ionization chambers (4π-ICs). This study addresses this gap by investigating the optimization of key measurement parameters—time and source-to-detector distance—in order to improve the accuracy and efficiency of 4π-ICs used in nuclear medicine and standardization laboratories. The stability of the chamber was assessed using ionization currents from a reference source of holmium-166m (166mHo). Linearity testing was conducted with three iodine-131 (131I) sources at varying activity levels. Measurements were performed over durations ranging from 10 to 80 seconds and distances from 3.00 to 7.00 cm, with standard conditions set at 40 s and 4.00 cm. The measured half-life of 131I was 8.0225 ± 0.0004 days, consistent with published values, and the uncertainty averaged ±0.024% (k = 1). A distance of 3.50 cm produced results similar to 4.00 cm but with reduced uncertainty. The optimal measurement condition was determined to be 35 s at 4.50 cm. This work offers a novel, statistically validated approach for optimizing 4π-IC use, enhancing radiation safety, reducing radioactive material consumption, and improving productivity in radioisotope laboratories.