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At 5:29 a.m on July 16, 1945, the world’s first atomic bomb was detonated at the Trinity Test Site in New Mexico.
Fast-forward many decades, and today people are illegally stealing pieces of old, sunken ships for big bucks.
These two things might not seem like they have anything in common, but they are actually intimately linked.
Learn more about low-background steel, what it is and why there is demand for it, on this episode of Everything Everywhere Daily.
Over the course of this podcast, I’ve covered some of the most important people in history, empires that have conquered much of the world, and technologies that have changed our civilization.
… this is not such an episode.
In the big scheme of things, the topic of this episode is pretty minor. There are very few people who actually have to deal with it firsthand, and I’m guessing that the vast majority of you have never even heard of low-background steel or know what it is.
The reason why it is the subject of an episode is that it is really, really interesting. I’m pretty sure that this is going to be the type of episode that many of you will be annoying people with tomorrow.
I’ll start with a short overview of the steel-making process that I covered in a previous episode.
Modern steelmaking was revolutionized by the Bessemer process. The Bessemer process converts raw pig iron into steel by blowing enormous quantities of air through molten iron.
After World War II, the steel industry converted to the basic oxygen steelmaking process, which blows pure oxygen rather than air into the iron. Even though oxygen is used, it is still taken from the atmosphere, which is the crux of the entire episode.
Now, I want to shift gears and go back to what I mentioned in the introduction: The Trinity Atomic Test in July 1945.
When the atomic bomb was detonated, the world changed. By that, I don’t mean that in a social or cultural sense, although that certainly was true. I mean it in a very literal and physical sense.
The atomic bombings of Hiroshima and Nagasaki followed in August. Then came hundreds of atmospheric nuclear weapons tests by the United States, Soviet Union, Britain, France and China.
The largest period of atmospheric testing occurred during the 1950s and early 1960s. The most commonly cited number is that 528 atmospheric nuclear explosions took place on Earth from 1945 to 1980.
The United States, Great Britain, and the Soviet Union ended atmospheric tests in 1963, France continued until 1974, and China conducted the world’s final atmospheric nuclear test in 1980.
Atmospheric explosions produce enormous quantities of radioactive particles close to the test site. But high-yield thermonuclear explosions are powerful enough to inject fine radioactive material into the stratosphere.
Once there, the material could remain aloft for months or years and circulate around much of the planet before falling out.
The result of these explosions was a slight increase in background radiation across the Earth.
Some of the isotopes that have been put into the atmosphere include:
iodine-131
strontium-89 and strontium-90
cesium-137
carbon-14
tritium
zirconium-95
ruthenium-106
cerium-144
Does this mean that you’ve been exposed to this radiation? Yes, you have. All of us. Me, you, everyone who has been alive over the last 80 years or so.
However, this isn’t as big a deal as you might think. Putting aside the isotopes that were put into the atmosphere due to nuclear testing, there is background radiation that we are all exposed to every minute of every day.
The average person will receive 3.0 millisieverts of radiation per year. This is an average, and there is a great deal of variation depending on where you live. Radiation can come from the ground, from the air via breathing natural elements such as radon, cosmic rays, and from natural isotopes like potassium-40.
If you live in an area with higher levels of natural uranium in the ground, or if you live at a higher elevation with more exposure to cosmic rays, you’ll get more radiation exposure. Likewise, flying, medical procedures, and other things can also increase your natural exposure.
However, humans have adapted to this baseline background radiation over hundreds of thousands of years, and it really isn’t something you need to worry about.
So how did nuclear tests affect global background radiation?
According to the United Nations Scientific Committee on the Effects of Atomic Radiation, the average worldwide annual radiation dose attributable specifically to atmospheric weapons fallout peaked around 1963 at about 0.11 mSv per person per year.
In other words, at the worldwide peak, weapons fallout was adding roughly 3 to 4 percent to the average person’s natural radiation dose. So it was a real increase, but a very minor one.
Since it peaked in 1963, it has decreased over time as the isotopes have decayed, and today it is about 0.003 mSv/year. In other words, it is one-tenth of one percent of the average natural background radiation exposure.
So, if this happened and the impact on the environment is real but minor, what is the problem, and why am I doing a podcast episode about it?
It goes back to the Bessemer process. Because all of the oxygen blown over the iron comes from the atmosphere, it is contaminated, even if only slightly.
That means you get steel which is slightly contaminated with radiation. It isn’t much, and for the vast, vast majority of steel uses it doesn’t matter and isn’t even noticeable. However, a few very specialized applications care a great deal about this contaminated steel.
These specialized applications require steel with low levels of background radiation, hence the term low-background steel.
Low-background steel is primarily used when scientists need to detect extremely faint amounts of radiation. It has been used to construct shielding for whole-body radiation counters, gamma-ray spectrometers, nuclear safeguard equipment, and instruments that measure trace amounts of radioactive contamination in food, soil, water, biological samples, and industrial materials.
Because ordinary steel can contain minute amounts of radioactive isotopes, using exceptionally low-radioactivity steel reduces the background noise that might otherwise interfere with these measurements.
It is also important in highly sensitive particle-physics experiments searching for rare phenomena such as dark matter interactions and neutrino events. In these experiments, radioactive decay in the detector’s own structural materials can mimic or obscure the signals researchers are trying to detect.
So, where do you get low-background steel from if all the air on Earth is contaminated?
The answer is: you get it from the past. You have to get it from steel that was made before 1945.
Where can you find large amounts of pre-1945 steel? Old bridges, industrial machinery, railroad equipment, and buildings are possible sources.
However, these sources have a problem. Cosmic rays from space can collide with atoms in metals, converting them into radioactive isotopes through a process called cosmogenic activation.
This means that any steel exposed to high levels of cosmic rays will also be contaminated. That includes most of the steel on the Earth’s surface.
One source of pre-1945 steel has been protected from most cosmic rays. It has the lowest background radiation rates you can reasonably find anywhere on Earth: shipwrecks.
Metal that has spent decades underwater receives shielding from cosmic radiation, at least much more than steel that has been on the surface.
Historically, one of the best sources of such steel has been Scapa Flow in the Orkney Islands of Scotland. In 1919, after the end of the First World War, 52 ships from the German Navy’s High Fleet were scuttled.
Much of the fleet was salvaged for scrap during the 1920s and 1930s, but the surviving wrecks became historically important archaeological and diving sites, and destructive salvage was increasingly restricted.
Because low-background steel is so hard to find, it has become very valuable. This has led to illegal harvesting from shipwrecks.
Illegal salvage of low-background steel has most notoriously involved World War II shipwrecks in Southeast Asian waters, including British, Dutch, Australian, American, and Japanese warships.
Perhaps the best-known case involves HMS Prince of Wales and HMS Repulse, sunk by Japanese aircraft off Malaya on December 10, 1941. The wrecks are graves for more than 800 sailors.
They suffered years of unauthorized salvage, but the case attracted renewed attention in 2023 when the Chinese salvage vessel Chuan Hong 68 was observed working over the sites with a large crane and dredging equipment. Investigators alleged that it was tearing apart the wrecks to recover steel.
An even more dramatic episode occurred in the Java Sea, where several major Allied warships effectively disappeared. When researchers returned in 2016 to wrecks from the 1942 Battle of the Java Sea, they discovered that the Dutch cruisers HNLMS De Ruyter and HNLMS Java had been almost completely removed, while much of the destroyer HNLMS Kortenaer was gone.
British wrecks suffered a similar fate. HMS Exeter and HMS Encounter were found to have been almost entirely dismantled, while HMS Electra was badly damaged. In some places, sonar showed little more than depressions in the seabed where entire warships had once rested.
The problem isn’t just low background steel. The devices that require low-background steel also need other low-background materials. Copper, lead, titanium, plastics, ceramics, solder, cables, and even electronic components may contain tiny traces of radioactive isotopes. In experiments looking for extremely rare events, such as dark matter interactions, even a few extra radioactive decays can matter.
Lead is especially useful because its high density makes it an excellent shield against gamma radiation, but newly produced lead commonly contains radioactive lead-210, which has a half-life of about 22 years.
Ancient Roman lead, especially ingots recovered from shipwrecks, has been buried or submerged for roughly two thousand years, allowing essentially all of its original lead-210 to decay away. That makes it exceptionally attractive for shielding modern ultra-sensitive detectors.
The downside is that Roman lead is also an archaeological artifact, so melting ancient ingots for scientific equipment can destroy irreplaceable historical evidence.
Today, researchers often use carefully selected low-background modern lead, reserving ancient lead for cases where its unusually low radioactivity offers a clear scientific advantage.
In an interesting twist, low-background steel has become a metaphor for internet content created before the rise of large language models.
Just as pre-1945 steel predates contamination from nuclear fallout, content created before AI became widespread predates the possibility that it was produced by large language models.
Researchers may therefore value older books, websites, archives, and datasets as relatively “clean” examples of human-generated material when training or evaluating AI systems.
The good news is that every year that passes without another atmospheric nuclear test means that the need to hunt down low-background steel at the bottom of the sea becomes less and less.
However, the demand is not quite zero yet.
What low-background steel illustrates is that things can have unforeseen and unintended consequences. When the Trinity test was conducted in 1945, no one could have imagined that it would lead to people scavenging metal from the sea floor, yet that is exactly what happened.