The correct option for the question regarding which material is most effective for shielding against high-frequency electromagnetic radiation, such as X-rays and gamma rays, is **C. Lead**. ### Detailed Explanation 1. **Understanding Electromagnetic Radiation**: - High-frequency electromagnetic radiation, such as X-rays and gamma rays, has very short wavelengths and high energy. This type of radiation can penetrate many materials, which is why effective shielding is crucial in environments where exposure to such radiation occurs, such as in medical imaging or nuclear facilities. 2. **Material Properties**: - The effectiveness of a material in shielding against radiation depends on its density and atomic number. Denser materials with higher atomic numbers are generally more effective at absorbing and scattering high-energy photons. 3. **Lead as a Shielding Material**: - **Density**: Lead is a very dense material (approximately 11.34 g/cm³), which means it has a lot of mass in a small volume. This density helps to absorb and scatter the high-energy photons of X-rays and gamma rays. - **Atomic Number**: Lead has a high atomic number (82), which increases the likelihood of interactions between the lead atoms and the incoming radiation. The higher the atomic number, the more effective the material is at attenuating radiation. 4. **Comparison with Other Options**: - **A. Wood**: Wood is much less dense (about 0.6-0.9 g/cm³) and has a low atomic number (6 for carbon, the primary element in wood). This makes it ineffective for shielding against high-energy radiation, as it cannot absorb or scatter the radiation effectively. - **B. Aluminum**: Aluminum is denser than wood (about 2.7 g/cm³) and has a higher atomic number (13), but it is still not as effective as lead. While aluminum can provide some shielding, it requires a much thicker layer compared to lead to achieve similar levels of protection against X-rays and gamma rays. - **D. Plastic**: Plastic is even less dense than aluminum (typically around 0.9-1.4 g/cm³) and has a low atomic number (varies, but generally around 6 for carbon). It is not effective for shielding against high-frequency radiation, as it lacks the necessary density and atomic structure to absorb or scatter the radiation effectively. ### Summary of Key Points - **Lead is the most effective material for shielding against X-rays and gamma rays due to its high density and atomic number.** - **Wood, aluminum, and plastic are less effective because they have lower densities and atomic numbers, making them inadequate for high-energy radiation shielding.** - **When selecting materials for radiation shielding, consider both density and atomic number for optimal effectiveness.** ### Revision Summary - **Lead is the best choice for shielding against high-frequency electromagnetic radiation.** - **Density and atomic number are critical factors in determining a material's effectiveness as a shield.** - **Wood, aluminum, and plastic are significantly less effective than lead for this purpose.** - **Always assess the specific radiation type and energy when choosing shielding materials.**