Reactor-Driven Neutron Sources from the ²⁰⁷Pb(γ,n) and ²⁰⁵Tl(γ,n) Reactions

Monoenergetic gamma beams (Δ ~ 10 eV) based on thermal neutron capture, in a nuclear reactor, using the V(n,γ) and Fe(n,γ) reactions were utilized for generating fast neutron sources from lead and thallium, respectively, via the ²⁰⁷Pb(γ,n) and ²⁰⁵Tl(γ,n) reactions. It so happens that one of the incident gamma lines of the V source, E_γ = 7163 keV, photoexcites by chance a resonance level in ²⁰⁷Pb, which emits neutrons at an energy of 423 keV. In a similar manner the incident gamma line at E_γ = 7646 keV of the Fe(n,γ) source photoexcites by chance a resonance level in the ²⁰⁵Tl isotope, which emits neutrons at an energy of 99 keV. The cross sections for the neutron emission process were measured and found to be σ(γ,n) = 35 ± 6 mb and 107 ± 17 mb, respectively, with intensities of the order of 10⁴ n/s.