Low-background steel is any steel produced prior to the detonation of the first nuclear bombs in the 1940s and 1950s. Typically sourced from shipwrecks and other steel artifacts of this era, it is often used for modern particle detectors because more modern steel is contaminated with traces of nuclear fallout.
Since the cessation of atmospheric nuclear testing, background radiation has decreased to very near natural levels, making special low-background steel no longer necessary for most radiation-sensitive applications, as brand-new steel now has a low enough radioactive signature that it can generally be used in such applications. However, some demand remains for the most radiation-sensitive applications, such as Geiger counters and sensing equipment aboard spacecraft, and World War II-era shipwrecks near in the Java Sea and western South China Sea are often illegally scavenged for low-background steel.
From 1856 until the mid 20th century, steel was produced in the Bessemer process, where air was forced into Bessemer converters converting the pig iron into steel. By the mid-20th century, many steelworks had switched to the BOS process, which uses pure oxygen instead of air. However, as both processes use atmospheric gas, they are susceptible to contamination from airborne particulates. Present-day air carries radionuclides, such as cobalt-60, which are deposited into the steel, giving it a weak radioactive signature.
World anthropogenic background radiation levels peaked at 0.11 mSv/yr above natural levels in 1963, the year that the Partial Nuclear Test Ban Treaty was enacted. Since then, anthropogenic background radiation has decreased to 0.005 mSv/yr above natural levels. This is low enough that, in 2010, Straight Dope said that "reduced radioactive dust plus sophisticated instrumentation that corrects for background radiation means new steel can now be used in most cases".
- Aaron, D. Jayne; Berryman, Judith (1997). "Rocky Flats Plant, Emergency Medical Services Facility". U.S. Department of Energy, Office of Legacy Management. HAER No. CO-83-S (Rocky Flats Plant, Building 122). Archived from the original on 8 June 2019.
- Sources and Effects of Ionizing Radiation. United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (Report). Vol. I. New York: United Nations. 2010 . p. 6. ISBN 978-92-1-142274-0. UNSCEAR 2008 Report.
- Adams, Cecil (10 December 2010). "Is steel from scuttled German warships valuable because it isn't contaminated with radioactivity?". The Straight Dope.
- "The world's biggest grave robbery: Asia's disappearing WWII shipwrecks". The Guardian.