Associate Safety Professional Practice Exam

Which of the following substances would be an effective shield for gamma but not neutron emissions?

1. Steel

2. Lead

3. Water

4. Concrete

The correct answer is: Lead

Lead is an effective shield for gamma radiation because of its high atomic number and density, which help attenuate gamma rays more efficiently than many other materials. Gamma radiation, being highly penetrating, interacts primarily with matter through photon interactions, such as the photoelectric effect, Compton scattering, and pair production. Lead's ability to absorb and scatter gamma photons makes it a preferred material in radiological protection for such emissions. However, when it comes to neutron radiation, lead is not as effective. Neutrons are uncharged particles and primarily interact with matter through nuclear reactions and elastic scattering, meaning they are better attenuated by materials rich in hydrogen (like water or polyethylene) or materials with low atomic numbers. Therefore, while lead provides excellent shielding against gamma radiation, it does not effectively shield against neutron emissions. This distinct capacity to shield against gamma but not against neutrons is what establishes lead as the correct answer in this context.