books.google.de - In the United States there are several thousand devices containing high-activity radiation sources licensed for use in areas ranging from medical uses such as cancer therapy to safety uses such as testing of structures and industrial equipment. Those radiation sources are licensed by the U.S. Nuclear...http://books.google.de/books/about/Radiation_Source_Use_and_Replacement.html?hl=de&id=3cT2REdXJ98C&utm_source=gb-gplus-shareRadiation Source Use and Replacement
