system
Given the following post, respond as if you're commenting on Reddit:
human
Why is Lead a good radioactive shield?
gpt
Lead (and other dense metals like cadmium) are good at shielding gamma radiation because they are dense. High atomic number and relatively short bond length means there are a lot of electrons for incoming photons to interact with. When the photons that make up the gamma radiation interact with the electrons and transfer energy to them. The same will happen with any material with electrons, but dense metal has more electrons, so better attenuation.

Lead is not so good for other types of radiation. Alphas are massive and have high charge so are stopped by almost anything, including lead, but also paper and several centimeters of air. Betas will be stopped by lead but produce x-rays in the process (Bremsstrahlung radiation) so they are better shield by a lighter material like tin or plastic.

Neutrons are a different story. They are uncharged and don't interact with electrons. To shield neutrons you must get them to collide with a nucleus and transfer energy to it, slowing the neutron down. The energy transfer happens best when the nucleus is of similar mass to the neutron (ie, a H nucleus). For this reason, materials with lots of hydrogen are best for neutron shielding. Paraffin wax is often used.