What material is most effective at absorbing gamma radiation?

Lead is a dense material and is particularly effective at absorbing gamma radiation due to its high atomic number (Z) and density. Gamma rays, which are high-energy electromagnetic radiations, have a high penetration ability and can easily pass through many materials. However, dense materials like lead are capable of attenuating these rays significantly.

The effectiveness of a material at absorbing gamma radiation depends largely on its density and atomic number. Lead provides sufficient thickness and mass, which allows it to effectively dissipate the energy of gamma photons through interactions such as photoelectric absorption and Compton scattering. The few centimeters of lead required to achieve effective gamma radiation shielding demonstrates its capability in practical applications where radiation protection is essential.

In contrast, while several kilometers of air can reduce gamma radiation intensity, the amount required is impracticably large compared to the thickness of lead needed for effective shielding. Stainless steel, while strong and durable, does not provide as much attenuation as lead does due to its lower density and atomic number. Concrete can offer some level of gamma radiation absorption, but again, it requires a much thicker barrier compared to lead to be equally effective. Therefore, lead stands out as the most effective material for gamma radiation shielding in this context.