Thermal neutron flux determination of a ²⁴¹Am-Be source using cobalt chloride salt as an alternative activation...

A methodological approach is reported to determination of the thermal neutron flux from a sealed ²⁴¹Am-Be source using neutron activation analysis (NAA). Unlike conventional approaches based on metallic foils (Au, In, Co), cobalt chloride hexahydrate (CoCl₂⋅6H₂O) was employed as an alternative activation medium. A 2.14 g cobalt sample was irradiated at a fixed distance of 13±1 cm inside a paraffin moderator for 20 days, and the induced ⁶⁰Co activity was quantified by gamma spectrometry. Detector efficiency was evaluated experimentally and refined by Monte Carlo simulations accounting for volumetric geometry, while self-absorption corrections were determined analytically. The measured thermal flux at the sample position was ϕ_th=(6.39±0.75)×10³n cm^-2s^-1, corresponding to an equivalent thermal emission rate of S_th≈(8.5±0.5)×10⁶n s^-1. Assuming a thermalization fraction for paraffin moderation f_th=0.225±0.043, and using the measured S_th=(8.5±0.5)×10⁶n s^-1, the total source emission is S_tot=S_th/f_th≈(3.8±0.8)×10⁷n s^-1, in agreement with the manufacturer's nominal value of 4.7×10⁷n s^-1 (decay-corrected). These findings demonstrate that cobalt chloride salt is a practical and reliable activation material for neutron flux characterization, particularly when metallic foils are unavailable.