Investigation of sodium-22 positron source production at tehran research reactor: A comprehensive simulation-based feasibility study with FLUKA and EMPIRE code comparison

This is the authors' abstract. We don't add key points for this paper.

Sodium-22 (²²Na) is a long-lived positron-emitting radionuclide with extensive applications in positron physics, detector calibration, positron-annihilation spectroscopy, and nuclear medicine research. This comprehensive study investigates the feasibility of producing a ²²Na positron source using the Tehran Research Reactor (TRR), a 5 MWth pool-type, light-water-moderated and cooled research reactor located at the Nuclear Science and Technology Research Institute (NSTRI) in Tehran, Iran. The principal neutron-induced pathway considered is ²³Na(n,2 n)²²Na, which requires a fast-neutron component and is therefore strongly dependent on the high-energy tail of the neutron spectrum rather than on the nominal thermal flux alone. A complementary direct photonuclear route, ²³Na(γ,n)²²Na, is discussed as a possible secondary contribution, while indirect production through intermediate radionuclides is assessed as a less attractive route for TRR conditions. A detailed, transport-compatible target model was defined for a high-purity sodium target enclosed in an aluminum capsule and placed in a representative high-flux irradiation position. The production rate was evaluated from the spectral reaction-rate integral and compared between a FLUKA transport treatment and an EMPIRE nuclear-reaction calculation. The comprehensive analysis indicates that the dominant limitation is the small fast-neutron fluence available at a thermal research reactor, with the FLUKA and EMPIRE simulations showing an 8% difference in production rate estimates. The principal methodological advantage of combining FLUKA and EMPIRE is the separation of neutron transport from nuclear-reaction modeling. The results support further detailed activation calculations using the actual TRR irradiation-position spectrum, validated cross sections, target mass, and operating schedule. This study provides a comprehensive framework for evaluating ²²Na production in research reactors and establishes benchmark specifications for future experimental validation.