Which of the following is used for shielding radioactive fallout?

Step 1: Analyze the question The question asks which material is used to shield against radioactive radiation (alpha, beta, and especially gamma rays and X-rays).

Step 2: Explain the concept Shielding works by absorbing or attenuating radiation. The best shielding materials for penetrating radiation like gamma rays have:

• High density
• High atomic number (Z), meaning many electrons to interact with the photons

Here is how the different radiations are stopped:

• Alpha particles: stopped by paper or skin
• Beta particles: stopped by thin aluminum or plastic
• Gamma rays: need thick, dense material such as lead or concrete

Step 3: Evaluate the options

• A. Aluminum: stops beta particles, but only weakly attenuates gamma rays.
• B. Lead: very dense (about 11.3 g/cm³) with a high atomic number (82). It absorbs gamma rays and X-rays very effectively.
• C. Iron: reasonably dense and sometimes used, but less effective than lead per unit thickness.
• D. Plastic: low density, so it is good only for stopping beta particles.
• E. Wood: low density, so it gives almost no protection against penetrating radiation.

Step 4: Answer Lead is the standard material for shielding radioactive emissions. It is used in lead aprons, containers for radioactive sources, and the walls of X-ray rooms.

Tip: Remember "Lead for Leaks": when the question is about shielding gamma or X-rays, think of lead first, because its density and high atomic number make it the best of these options. For beta particles, think of aluminum or plastic.