On 16 July 1945, the world changed forever when Manhattan Project scientists detonated the world’s first atomic bomb.
The Trinity Test left a radioactive legacy, as did the subsequent decades of above-ground nuclear testing (528 detonations in total) that filled the atmosphere with radioactive particles.
The air we breathe is now slightly more radioactive. This has had unexpected consequences for some of the materials we produce.
Steel, for instance, is made by forcing purified oxygen through molten iron ore. But because today’s air is subtly radioactive, so is the steel we produce.
Fallout from weapons testing peaked in 1963, and levels have since dropped by more than 95 per cent as the radioactive particles in the atmosphere have gradually decayed.
The steel we make today isn’t a health threat, but its faint radioactivity can still interfere with sensitive scientific equipment, such as instruments built to detect dark matter.
Scientists now have to seek out material with minimal radiation contamination. Steel produced before the first nuclear detonations in 1945 contains significantly fewer radioactive particles, making it valuable in particle physics research.
Most of this 'low-background steel' is salvaged from shipwrecks, such as the fleet of 52 German battleships abandoned in the shallow waters of Orkney, Scotland.
The demand for low-background steel has sparked controversy, however. In 2017, news broke that up to 40 WWII-era warships had been illegally plundered by salvage divers around Singapore, Indonesia and Malaysia.
The discovery caused outcry among veterans and historians, who respect the wreckages as underwater war graves.
Ancient Roman lead is also prized among physicists for shielding ultra-sensitive experiments from background radiation. Lead ore is naturally radioactive. Once it’s been processed, it still contains trace amounts of the isotope lead-210, which has a half-life of 22 years.
While it would take centuries for freshly-mined lead to become suitable for use in particle physics, lead mined by the Romans has had plenty of time to lose its radiation.
In 2010, Italy’s National Archaeological Museum honoured a long-standing agreement, handing over 120 lead ingots – recovered from a Roman ship that sank around 80-50 BC – to the National Institute of Nuclear Physics to be melted down and used to shield an upcoming experiment.
This article is an answer to the question (asked by Henry Becker, Durham) 'How does background radiation affect particle detectors?'
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