Abstract: Lead-bismuth eutectic (LBE: 44.5% Pb+55.5% Bi) alloy is a primary candidate coolant for Generation IV reactors due to its favorable physicochemical properties. However, radioactive polonium hazards arising from the use of molten LBE as the primary reactor coolant now represent a major challenge that must be addressed in the development of lead-bismuth-cooled reactors. The ²⁰⁹Bi(n,γ)^210gBi reaction serves as the primary source term for ²¹⁰Po production in lead-bismuth-cooled reactors. Precise measurement of the ²⁰⁹Bi(n,γ)^210gBi reaction cross-section is critical for evaluating the radioactive polonium release risk from such reactors. Offline radiochemical analysis of ²¹⁰Po (the decay product of ^210gBi) constitutes one method for determining this neutron capture cross-section. This paper addresses the ²¹⁰Po background radioactivity during preliminary target preparation. Experimental results reveal significant variations in ²¹⁰Po concentration across different batches of pure bismuth materials. Traceability analysis confirms the presence of varying levels of ^210gBi and ²¹⁰Po in the target materials, which do not satisfy radioactive equilibrium conditions. Combined with TALYS-2.0 simulations, we evaluated the impact of radioactive polonium in target materials on the measurement of the ²⁰⁹Bi(n,γ)^210gBi reaction cross-section at fission-relevant average neutron energies. Theoretical analysis demonstrates that selecting ultra-low-activity bismuth targets (with minimal ²¹⁰Po concentration) effectively reduces α particle background interference during ²⁰⁹Bi(n,γ)^210gBi measurements. This approach significantly enhances the accuracy of fast-neutron capture cross-section determinations for ²⁰⁹Bi.