Taking a Gander with Gamma Rays

摘要

Since their discovery in 1895, x rays have been used in countless applications to make the unseen visible—bones beneath skin and tissue, metal beneath plastic. These electromagnetic waves can penetrate low-density materials (such as skin and plastic), but higher density materials (bone and metal) significantly scatter or absorb photons. Recording the photons that pass through only some materials creates the distinctive "shadow picture" of an x-ray image, which shows a feature previously hidden from view. In special cases, scientists can use x-ray imaging to determine the atomic composition of matter—that is, its constituent elements. Determining the isotopic variety of observed elements would also be useful for some applications, for example, to distinguish depleted uranium from weapons-grade uranium. However, developing those capabilities requires a radiographic source that uses the next higher energy range in the electromagnetic spectrum.