If you want to build a Geiger counter you need to first find a shipwreck from before 1945.
In 1855 Henry Bessemer came up with a process to cheaply manufacture steel. The Bessemer process removes the impurities (such as excess carbon and silicon) from pig iron by blowing air through the molten metal. It made steel affordable for the first time, and so was responsible for the huge growth in railroads in the second half of the 19th century.
Jump forward to July 16, 1945. The first nuclear bomb test was set off in New Mexico. For the first time, human-generated radiation enters the atmosphere. With the huge proliferation in nuclear tests across the mid-20th century, background radiation in the air went up worldwide… and when that air was blown through pig iron, the radioactive contamination got into the steel. Don’t panic! The levels of radiation in the atmosphere peaked in 1963 and has gone down every year since. But all steel made since 1945 has some level of background radiation effectively baked into it.
This is not a problem for most uses of steel. Sometimes, though, you really need steel without that radioactive contamination. Geiger counters, which measure radiation levels, are a good example. If you make a Geiger counter out of contaminated steel the instrument will pick up its own radiation. Many medical instruments need to detect radiation at very refined levels – so they cannot be made out of this steel either. What’s the solution? Easy, you find steel that was made before all this radioactive contamination.
Jump to June 1919. The First World War had just ended. The German naval fleet was docked at Scapa Flow, in the Orkney Islands of Scotland, while the various governments argued over what to do with it. On the 21st of June the German admiral in charge of the fleet ordered all the ships to be scuttled so they could not be given to another nation. Fifty-two ships sunk to the bottom of the shallow bay.
The steel from the sunken ships of Scapa Flow was made before the first nuclear tests. It is free of the background radiation present in all post-1945 steel. The technical term is “low-background steel.” Those shipwrecks have been pulled up from the deep, and the antique salvaged steel is used to make Geiger counters and medical equipment even today.