Analysis of iodine-126 contamination in the production of iodine-125 at the IEA-R1 reactor for brachytherapy applications

Abstract This work developed a method to determine the contamination rates of iodine-126 ( 126 I) in the sodium iodide (NaI) solution used in the production of iodine-125 ( 125 I) seeds for brachytherapy. The production of 125 I is carried out at the IEA-R1 Reactor of the Nuclear and Energy Research Institute (IPEN-CNEN/SP) by irradiation with natural xenon. For the radionuclide analysis, a High-Purity Germanium (HPGe) radiation detector (ORTEC model GEM-C5970-B, coaxial detection system and beryllium window, nominal efficiency of 43% at 1333 keV of cobalt-60) was used, in which the activity of 125 I was determined by the sum-peak method and the activity of 126 I by an efficiency curve using a 166 m Ho calibration source (A = (1832 ± 2) Bq, T 1/2 = 1.20 × 10 3 years and reference date: Feb 23rd 2024). The results demonstrated the predictions of 125 I production in the IEA-R1 Reactor with 126 I contamination levels below 0.005%, meeting the production requirements for clinical use.