Low inten­sity ionizing radiation present on the surface of the earth and in the atmosphere as a result of cosmic radiation and the presence of radio­isotopes in the earth’s rocks, soil, and atmosphere. The radioisotopes are either natural or the result of nu­clear fallout or waste gas from power stations. Background counts must be taken

A rearrangement that can occur in some polymerization reactions involving free radicals. A radical that has an unpaired electron at the end of the chain changes into a radical with the unpaired electron elsewhere along the chain, the new radical being more stable than the one from which it originates. For ex­ample, the radical RCH2CH2CH2CH2CH2CH2·  may

Any of a group of re­lated alloys used for making bear­ings. They consist of tin containing antimony (about 10%) and copper (1-2%), and often lead. The original alloy was invented in 1839 by the US inventor Isaac Babbit (1799-1862).