For high energy gamma radiation, which shielding material listed here is most commonly used because of its very high effectiveness in stopping or strongly attenuating gamma rays?

Introduction / Context:
Gamma rays are a highly penetrating form of ionising radiation that can pass through the human body and thick layers of material. Effective protection from gamma radiation is vital in medical imaging, nuclear power plants and radiation laboratories. Different materials offer different levels of shielding, mainly depending on their density and atomic number. This question asks which material among the options is most commonly used because of its high effectiveness in stopping or strongly attenuating gamma rays.

Given Data / Assumptions:

• Gamma rays are high energy photons with no mass and no charge.
• Shielding effectiveness for gamma rays increases with material density and atomic number.
• Lead is a very dense metal with a high atomic number.
• Steel and concrete are also used for shielding but have different densities and compositions.

Concept / Approach:
Gamma ray attenuation in matter occurs through processes such as photoelectric absorption, Compton scattering and pair production. The probability of these interactions generally increases with the atomic number of the shielding material and its density. Lead has a very high density and a high atomic number, which makes it particularly effective for gamma ray shielding. That is why thin sheets of lead can significantly reduce gamma radiation levels. Steel and concrete also provide shielding, but for the same level of protection they usually require much greater thickness compared with lead. Therefore, when asking which material is most commonly used due to its high effectiveness, lead is the best choice.

Step-by-Step Solution:
Step 1: Recall that gamma rays are penetrating and require dense materials for effective shielding.Step 2: Recognise that lead has a high atomic number and high density, which makes it very effective at absorbing gamma photons.Step 3: Note that steel, although useful and stronger structurally, has a lower atomic number and generally requires thicker sections to match lead shielding.Step 4: Understand that concrete is used for large scale shielding, but again, much thicker walls are needed compared to lead sheets.Step 5: Compare the practicality and common use: lead aprons in radiology, lead bricks in laboratories and lead linings in shields.Step 6: Conclude that lead is the most commonly used material for effective gamma shielding among the options.

Verification / Alternative check:
In hospitals, radiology departments use lead aprons and lead lined walls to protect staff and patients from X rays and gamma rays. Nuclear facilities often rely on lead bricks and lead glass around high radiation areas. While concrete biological shields are also widely used in reactors due to their structural advantages and cost, achieving the same attenuation as lead requires much more thickness. Physics handbooks usually present attenuation coefficients that show lead having higher attenuation per unit thickness for gamma rays than steel or concrete. These practical examples and data support lead as the most effective shielding material per unit thickness.

Why Other Options Are Wrong:
Structural steel provides some gamma shielding, but thickness must be significantly greater than that of lead to achieve the same attenuation. Concrete is also useful, especially in large structures like reactor buildings, but again requires much more thickness compared with lead, and its composition and density can vary. Saying that all materials are equally effective ignores the large differences in attenuation coefficients and would mislead about shield design. Therefore, lead is the single best answer when asked which material is most effective for gamma shielding in practice.

Common Pitfalls:
Students may think that any heavy or strong material works equally well for radiation shielding, or that thick concrete always provides better protection than thinner lead. Another confusion arises from mixing up neutron shielding, where materials like concrete or water are more effective, with gamma shielding. To avoid errors, remember that high density and high atomic number metals like lead are especially effective for gamma rays, which is why lead is so widely used in medical and industrial shielding.

Final Answer:
Lead is most commonly used as an effective shielding material against gamma radiation because of its high density and high atomic number.