The crystalline structure of gallium is orthorhombic. Natural gallium is made up of a mixture of two stable isotopes: gallium-69 (60.4%) and gallium-71 (39.6%). Somewhat chemically similar to aluminum, gallium slowly oxidizes in moist air until a protective film forms and becomes passive in cold nitric acid. Gallium has been considered as a possible heat exchange medium in nuclear reactors, although it has a high neutron cross section. Radioactive gallium-72 shows some promise in studying bone cancer; a compound of this isotope is absorbed by the cancerous portion of the bone. The most common use of gallium is in gallium scanning. Gallium scans are often used to diagnose and follow the progression of tumors or infections. Gallium scans can also be used to evaluate the heart, lungs, or any other organ that may be involved in an inflammatory disease. A gallium scan usually requires two visits to the Department of Nuclear Medicine. On the first day you receive an injection into a vein in your arm, you will be scheduled to return 2 to 5 days later, depending on