While most people wouldn’t be too excited about anything that came out of a sewer, Phillip Barbeau, a professor of physics at Duke University, tells me enthusiastically about 3 tons of lead that was recently pulled from Boston’s waste system. The metal, once used to seal pipes, is one of his more promising potential sources of “low-background” lead for his experiments. It’s now sitting at Los Alamos National Laboratory, the birthplace of the atomic bomb.
Low-background metals — most famously steel and lead — are valuable because they carry particularly low levels of radiation compared with most conventional materials. Used as shielding in advanced particle physics projects and for medical science devices like X-ray chambers, these metals won’t interfere with specialized, highly radiation-sensitive environments and tools.
[quote position=”full” is_quote=”true”]Each metal has its own story.[/quote]
The quest for these metals has led researchers, governments, and corporations to rip up old railways, raid sunken battleships, and disturb centuries-old artworks in the name of science.
Barbeau’s low-background steel supply, for example, is surplus World War II armor-ship plating that came from the Norfolk Navy Shipyard and was donated to Duke many years ago. His top source for low-background lead is a University of Chicago stockpile sourced from a 300-year-old sunken British ship. The lead, he says, “showed up with barnacles still on it.”
While some low-background materials can be freshly produced (like copper), the easiest route to most of these substances is a kind of scavenger hunt for metal manufactured before humans first split the atom.
As it turns out, the experiments and excesses of the nuclear age left much of the world’s metal at least slightly radioactive (whoops!). The first half of the 20th century, says Barbeau, didn’t just bring atomic blast tests and nuclear reactors around the world — it also created a kind of optimism about the potential for the related science, often without regard for long-term risks. “They were willing to use radioactivity as a tool,” Barbeau says.
“Some genius,” he says sarcastically, had the idea to start adding radioactive cobalt 60 to the lining of cauldrons where molten steel was prepared. Measuring the radiation, steelmakers could gauge whether the cauldron lining was wearing out, testing the integrity of the setup without the long process of cooling down the metal. The cobalt became mixed with the steel in tiny amounts, and now, because of the way we recycle steel, the cobalt has stuck around through the generations.
[quote position=”full” is_quote=”true”]The search for low-background was ‘the Wild West.'[/quote]
“Each metal has its own story,” Barbeau says. For example, lead is contaminated with potash, which is used as an additive in the smelting process, and “comes along with a lot of radon and daughter products of uranium and thorium,” he says. Other materials react to gases in the air, byproducts of nuclear reactor operation and blast tests. And on top of man-made radiation, cosmic rays can contaminate some metals left exposed to the air, adding to the problem.
Even with all this radioactivity talk, don’t get the impression run-of-the-mill metal is dangerous. When it comes to conventional steel, “we’re talking about radiation that’s lower than the radioactivity that naturally comes from a human,” Barbeau says. And yet even this tiny bit of radiation has been enough to drive seekers to surprising lengths in search of low-background metals.
Low-background stealing
In 2016, two British World War II warships that had been sunk in the Java Sea off Indonesia were found to have gone completely missing from their watery resting places, down to the last bolt. A number of media outlets reporting on the disappearances suggested salvagers went to such lengths because of the high price fetched by quality, low-background steel, like the metal from the ships’ armor plates.
Andrew Brockman, a U.K.-based archaeologist and maritime crime researcher, says it’s possible the low-background metal connection is real, but he’s still skeptical. “From the look of it, what they’re doing there is really crude, straight commercial salvage,” he says. Criminal investigative work into the black market for this kind of salvage is a fairly recent development, he says, and “the issue of low-background steel often gets quoted in the media” because of the “old stories about ships salvaged for low-background steel, including by governments.”
Certainly the U.S. government has scrapped and salvaged its own ships for low-background metals in the past. Last year, for example, Gizmodo obtained purchase orders made by Fermilab in Batavia, Illinois, which “reveal requests for tons of steel from heavy and light cruisers, ships like the Fall River, Astoria, the Roanoke, and the Topeka.” And plenty of commercial salvers, working within the law, have discovered and hauled up lucrative loads of low-background metals. On the Discovery Channel’s “Treasure Quest” series, one episode featured the recovery of low-background lead ingots worth millions.
But low-background metals have also probably earned their association with shady, possibly unethical activity.
In the mid- to late 20th century, Barbeau explains, the search for low-background metal was “the Wild West.” He says at one point, “people were driving around off the coast of Greece and Spain and Italy and paying off fishermen to tell them where the ancient Roman lead anchors were. And then pulling them up.”
At one point, computer chip makers were using low-background lead to prevent errors that could be triggered by a nearby alpha decay, Barbeau says. “And so the chip makers were actually driving the cost up so much, that supposedly they sent people to Europe to take down the old stained-glass windows that contained 300-year-old or 400-year-old lead and then replace it with modern lead.”
He tells me there’s a decent word-of-mouth system, where scientists pass on tips on stashes of low-background metals, like other people might pass along the number for a good weed dealer. “There are usually emails that pass around the national lab complex that say, ‘Oh, so-and-so is breaking down this old Department of Energy facility and they have this steel available, does anyone need it?’” Barbeau says. Barbeau has other (legitimate) contacts he doesn’t want to reveal — even with something of a regular supply out there, he wants to keep some of his low-background cards close to his chest.
When science and archaeology collide
Even when low-background metals are obtained through the proper channels, any time an archaeological site is disturbed or historically important materials are melted down and repurposed, there are ethical tradeoffs at play. Wrecks pursued by legal salvers are often historically insignificant merchant ships, but scientists also sometimes need access to something of a rarer vintage.
In May 2011, “a 2,000-year-old shipwreck’s cargo was used as a source for experiments of particle physics,” writes Elena Perez-Alvaro of Licit Cultural Heritage Ltd., which specializes in the preservation and use of archaeologically valuable materials. She tells me over email that in the 2011 case, the National Archaeological Museum of Cagliari in Sardinia allowed lead bricks from an ancient Roman ship to be used in a neutrino detector at the Italian National Institute of Nuclear Physics. An archaeologist at the Cagliari museum told the journal Nature that giving up the metal was a “painful” experience.
“Two civilizations that produced lead in a very careful way and produced a lot of it are the ancient Chinese civilizations and the Roman civilization,” Barbeau says. The Roman wreck used in 2011 fell “under the umbrella of the 2001 UNESCO Convention for the Protection of the Underwater Cultural Heritage,” says Perez-Alvaro, barring it from any kind of commercial use. However the Convention has no provisions for non-commercial scientific activities, and so the Roman vessel fell into a grey area.
Perez-Alvaro has written several papers on how to deal with scenarios where historical and scientific benefits might be at odds. “There is a need of dialogue” between scientists and archaeologists, she says. Those concerned with the past, she says, must develop a standard protocol for these situations, in which materials are “recovered under archaeological standards and always valuated by archaeologists.” Particle physicists and policymakers, on the other hand, need to be clear and honest about the importance of a given scientific project and the benefits it will bring mankind. “They need to consider where the limits are,” says Perez-Alvaro, “which sciences are ‘worth’ enough to use underwater cultural heritage.”
But evaluating the benefits of any one particle physics experiment can be a difficult task due to the field’s dense terminology, specialized knowledge, and the large amount of context one needs to take into consideration. A scientist can spend a lifetime attempting to prove, or disprove a single theory or search for a single particle, adding to our understanding of the universe and how it operates, even though many more steps (and years) would be necessary before that breakthrough yielded any practical or material benefits to the wider world.
Barbeau says his primary project using low-background metals right now is called Coherent, a project that looks for “certain types of very rare neutrino interactions, in particular something called coherent neutrino scattering.” He says last year they finally discovered the neutrino behavior they were looking for, nearly 40 years after it was first theorized.
“We now have a new way of probing and testing” their standard particle physics model, says Barbeau, “and so we’re very excited about being able to use this tool. And of course, low-background steel is one of the things that makes it happen.”
