Optimization and Validation of 4π Ionization Chamber for Precise I-131 Half-Life Measurement and Reduced Uncertainty

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 ( 166m Ho).Linearity testing was conducted with three iodine-131 ( 131 I) 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 131 I 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.