
The best place to find non-radioactive metal
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I recently saw a TV special with a segment about the German fleet that scuttled itself at Scapa Flow after World War I. They mentioned that metal salvaged from those ships was valuable to instrument makers because it hadn't been exposed to radiation from the atomic blasts at the end of World War II and later. Why is this metal different from metal recently mined and forged? It doesn't make sense that underwater steel would be more protected from radiation than ore still in the ground. Also, does radiation released in the last 65 years from atomic explosions really have that great an impact? - Mike N., Boise

So Mike, did the bastards who kept you locked up in that basement for the past 65 years really give you no access to information at all? If so, brace yourself for some news: First, a black guy is president. Second, the Cubs still haven't won a World Series. Third, radiation from atomic explosions is seriously bad.

In fairness, few today realize how many explosions there were. Prior to the 1963 atmospheric test ban treaty, the atomic powers (the U.S. and the former Soviet Union mostly, but also the UK, China, and France) among them detonated 502 nuclear devices with a total yield equivalent to 440 million tons of TNT at aboveground sites.

These tests (plus, of course, the two bombs dropped on Japan) threw vast amounts of radioactive crud into the air. The impact on instrument making was the least of the consequences. Global radiation exposure per person peaked in 1963. Scientists at the time estimated that radiation-induced genetic, bone, and bone marrow disease in children born during maximum fallout would be on the order of 5 percent above normal.

To gauge how bad things were, researchers built "iron rooms," shielded chambers in which people could be tested to see how much radioactivity they'd absorbed. These rooms had thick steel walls to prevent outside radiation from skewing the results. One iron room, at Argonne National Laboratory, was used to test Marshall Islanders who'd been accidentally exposed to fallout at Bikini atoll in 1954.

The challenge in iron rooms was that in those days new steel itself was contaminated, not because of problems with the ore, but because radioactive dust, mainly cobalt-60, got mixed in with the metal when huge quantities of air were blasted into the furnace during smelting. Small batches of uncontaminated steel could be made using special processes involving minimal air exposure, but that was pricey. Steel from pre-1945 warships was cheap.

That brings us to the German High Seas Fleet, interned with German skeleton crews aboard at the British naval base at Scapa Flow, off the Scottish coast, following the armistice of November 1918. Unsure whether hostilities would resume and determined that the fleet not be seized by the Allies, admiral Ludwig von Reuter ordered his men to scuttle their ships on June 21, 1919. Some 50-odd vessels were sunk.

A legend has grown up that much of the "low-background steel" from these ships was used in iron-room-type shielding applications, and in particular that NASA used some in the Voyager spacecraft. However, that's probably exaggerated -- most of the ships were salvaged in the 1920s and '30s. I did find a 1973 news account saying steel from the battleship Kronprinz Wilhelm was going to be used to shield a medical diagnostic system at a Scottish hospital, and that other pieces of the ship had been sent to Cape Town and Koblenz.

Fact is, plenty of old steel was available from decommissioned American warships. For example, 65 tons of armor plate from the battleship Indiana, scrapped in 1962, was used for shielding at an Illinois VA hospital, and another 210 tons went into building a shielded room at a Utah medical center.

Reduced radioactive dust plus sophisticated instrumentation that corrects for background radiation means new steel can now be used in most cases. There's some lingering demand for really old maritime metal, though. When researchers at one national lab wanted shielding that emitted no radiation whatsoever, they used lead ballast retrieved from the Spanish galleon San Ignacio, which had been lying on the bottom of the Caribbean for 450 years.