Investigation of Irradiation Position and Target Thickness Effect on Self-Shielding Phenomena and the Product Specific Yield of 60Co and 131I in TRR

The most important application of research reactors is the radioisotope production. Certain target nuclei exhibit a high neutron cross section and strong resonances, resulting in a phenomenon known as self-shielding. Computational calculations can significantly aid in determining the optimal irradiation position for any target to maximize product yield, specific yield, and minimize negative effects during the routine operation of a nuclear reactor. This study aims to investigate the irradiation of TeO₂ and cobalt metal targets in the Tehran research reactor at different irradiation positions. The simulation results indicate that for TeO₂ targets, there is no significant dependence of the self-shielding phenomenon on target thickness. It is evident that selecting internal irradiation boxes can enhance the yield of the ¹³¹I by a factor of 2 to 3, due to the increased neutron flux within the central irradiation boxes of the reactor core. Conversely, for ⁶⁰Co, a central irradiation unit could not be employed to achieve kilocurie activity because of the substantial negative reactivity it introduced into the TRR core.