An extraordinary incident occurred 20 years ago in Taiwan. Recycled steel, accidentally contaminated with cobalt-60 (half-life: 5.3 y), was formed into construction steel for more than 180
buildings, which 10,000 persons occupied for 9 to 20 years. They unknowingly received radiation doses that averaged 0.4 Sv – a collective dose of 4,000 person-Sv.
The experience of these 10,000 persons suggests that longterm exposure to radiation, at a dose rate of the order of 50 mSv (5 rem) per year, greatly reduces cancer mortality, which is a major cause of death in North America. Medical scientists and organizations may wish to seriously assess this and other current evidence in deciding whether chronic radiation could be an effective agent for enhancing defenses against cancer.