Explain why background radiation can vary with building materials or local geology.

Background radiation levels can vary significantly depending on local geology and building materials. Certain rocks, such as granite, contain higher concentrations of radioactive elements, leading to increased radiation exposure in areas with such geological formations. Additionally, building materials, like concrete or brick, may incorporate natural radioactive materials, further influencing the radiation levels indoors. Understanding these variations is crucial for assessing radiation exposure risks in different environments, ensuring safety and informed decision-making regarding construction and habitation.