= Solution
\b[Cadmium acts as an energy-selective <neutron> absorber in the stated comparison.] Its large thermal capture <collision cross-section> preferentially reduces the <thermal neutron> field reaching the source material, while its much lower fast-<neutron capture> probability allows more of the emitted fast <neutrons> to escape. This limits <thermal neutron>-induced changes in the source while retaining its qualitative role as a <neutron> emitter.
The point is selectivity between incoming thermal and outgoing fast components, rather than a claim that cadmium is transparent to every <neutron> or that capture produces no secondary radiation. This explains the stated material choice at a conceptual level; no source construction, cladding dimensions or irradiation specification follows from it.
Back to article page
