Replies

From Wikipedia:

"Low-background steel is any steel produced prior to the detonation of the first atomic bombs in the 1940s and 1950s. With the Trinity test and the Atomic bombing of Hiroshima and Nagasaki in 1945, and then subsequent nuclear weapons testing during the early years of the Cold War, background radiation levels increased across the world. Modern steel is contaminated with radionuclides because its production uses atmospheric air. Low background steel is so called because it does not suffer from such nuclear contamination. This steel is used in devices that require the highest sensitivity for detecting radionuclides.

The primary source of low-background steel is ships that were constructed before the Trinity test, most famously the scuttled German World War I battleships in Scapa Flow.[3]"