Great density concrete is primarily used for radiation shielding, counterweights, and other applications requiring high density. Because high density concrete shields better than low density concrete, it can guard against hazardous radiation such as X-rays, gamma rays, and neutrons. This material is also used in spacecraft construction because it is lighter than iron or aluminum and can be cost-effective for large structures such as telescopes. High density concrete has many advantages over other materials used in radiation shielding. It is more effective at blocking out radiation than lead or steel, for example. It does not retain radioactivity like wood does and therefore does not become radioactive itself. The density of high density concrete makes it useful for protecting subjects in medical experiments involving radiation exposure. This material is also used as an alternative to stone or earth for building foundations because it's resistant to compression damage from heavy loads. High density concrete is a popular material for making weights for ammunition. The weight of the concrete provides a strong anchor that prevents the projectile from flying away after it is fired. This type of concrete is also used when strength is important but volume is less critical. For example, it is commonly used by universities to make laboratory equipment that can withstand rough treatment without breaking. Concrete with a high sand content and long fibers from natural sources such as wood or coal can be used to make strong, light materials for use in buildings and structural components.