This book analyzes 10 C.F.R. 37, a new rule promulgated by the Nuclear Regulatory Commission (NRC) to protect radioactive material. "Byproduct material" includes specified types of radioactive material other than uranium or plutonium. The rule regulates byproduct material of types and in quantities that could be used to make a "dirty bomb." Congress attaches great importance to protecting the United States against terrorist threats and this rule will affect the many industrial, research, and medical activities nationwide that use radioactive materials, thereby affecting many constituents and raising cost-benefit issues. There is wide concern also about regulation and radiation.