The correct option for the material most commonly used for shielding against electromagnetic radiation in medical imaging applications, such as X-ray facilities, is **B. Lead**. ### Detailed Explanation 1. **Understanding Electromagnetic Radiation**: - Electromagnetic radiation includes a range of wavelengths, from radio waves to gamma rays. X-rays are a form of high-energy electromagnetic radiation that can penetrate various materials, which is why effective shielding is crucial in medical imaging to protect both patients and healthcare workers from unnecessary exposure. 2. **Properties of Shielding Materials**: - Effective shielding materials must have high density and atomic number to absorb or attenuate X-rays effectively. The higher the atomic number, the more likely the material is to interact with and absorb X-ray photons. 3. **Why Lead is the Best Choice**: - **High Density**: Lead has a high density (approximately 11.34 g/cm³), which means it can effectively block X-rays. The density of a material is crucial because denser materials have more mass per unit volume, which increases the likelihood of X-ray photons being absorbed or scattered. - **High Atomic Number**: Lead has an atomic number of 82, which is significantly higher than that of many other materials. This high atomic number contributes to its effectiveness in attenuating X-rays. - **Cost-Effectiveness**: Lead is relatively inexpensive compared to other heavy metals, making it a practical choice for widespread use in medical facilities. - **Malleability**: Lead can be easily shaped and formed into sheets or other configurations, allowing for versatile applications in walls, doors, and protective barriers in X-ray rooms. 4. **Analysis of Other Options**: - **A. Aluminum**: - While aluminum is lightweight and has some shielding properties, it has a lower density (approximately 2.7 g/cm³) and a lower atomic number (13). This makes it less effective at attenuating X-rays compared to lead. Aluminum is sometimes used in combination with other materials but is not suitable as a primary shielding material for X-rays. - **C. Copper**: - Copper has a higher density than aluminum (approximately 8.96 g/cm³) and a higher atomic number (29), but it is still not as effective as lead for X-ray shielding. Copper is often used in electrical applications and can provide some shielding against lower-energy radiation, but it is not the standard for X-ray facilities. - **D. Plastic**: - Plastic materials, such as polyethylene, are generally not effective for X-ray shielding. They have low density and atomic numbers, making them inadequate for blocking high-energy radiation like X-rays. Plastics may be used in other contexts, such as for protective equipment, but not as primary shielding in X-ray facilities. ### Summary of Key Points - **Lead** is the most effective material for shielding against X-rays due to its high density and atomic number. - **Aluminum** and **copper** are less effective due to lower density and atomic numbers. - **Plastic** is not suitable for X-ray shielding because of its low density and atomic number. - Lead is cost-effective and malleable, making it ideal for use in medical imaging facilities. ### Revision Summary - Lead is the primary material used for X-ray shielding due to its high density and atomic number. - Aluminum and copper are less effective alternatives. - Plastic is not suitable for X-ray shielding. - Understanding the properties of materials is crucial for effective radiation protection in medical imaging.