How shipwrecks and ancient Roman lead help physicists search for dark matter

When a 2,000-year-old Roman shipwreck was discovered off the Sardinian coast in 1988, it did not simply thrill archaeologists — physicists have been excited too.

The discovery grabbed the eye of 1 specifically: Ettore Fiorini, a particle physicist with Italy’s Institute for Nuclear Physics (INFN).

He did not care an excessive amount of in regards to the ship. He was extra thinking about its cargo — tons of of lead bars, every weighing 33 kilograms.

And as an alternative of displaying them in a museum, he deliberate to soften them all the way down to construct an underground observatory.

Dr Fiorini reached out to cultural heritage officers with a proposal. The INFN would help fund the restoration of the ingots if they may preserve some for themselves.

He believed this ancient lead may play an important position in uncovering the very nature of the Universe.

Why do physicists need ancient lead?

Ancient lead is helpful for delicate physics experiments as a result of it has misplaced the radioactivity that may complicate observations. 

When attempting to look at elementary particles, that are the tiniest constructing blocks that make up actuality, physicists must silence any background noise. 

For instance, particle detectors are sometimes saved deep in caves underground to keep away from showers of “cosmic rays”. 

These are high-energy particles that come from area, and whereas they don’t seem to be dangerous to people, they’ll disrupt experiments. 

“Every second of our life, every centimetre of our body is crossed by a particle,” Paolo Gorla, an INFN physicist, says.

“[Going underground] gives us some kind of cosmic silence.”

The detector additionally should be shielded from the radioactive “noise” that comes from throughout the cave itself. 

“The presence of a human or just the rock of the mountain, or even the banana I bring to eat on a break, can disturb the experiment,” Dr Gorla says. 

Lead is an appropriate protect from this radioactivity — which may come from cosmic rays or bananas — as a result of it is tremendous dense. 

But freshly mined lead has some radioactive “noise” of its personal, as a result of it naturally comprises a hint quantity of the unstable isotope lead-210, which releases vitality because it decays.

The radioactivity within the lead will totally decay, producing steady lead that is good for use as a protect — however solely after a number of hundred years.

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Which is why, in accordance with metallurgist Kevin Laws of the University of New South Wales, physicists are looking out for lead mined throughout ancient Roman instances. 

It has had loads of time to turn into steady.

“But there is debate that by utilising lead from sources such as shipwrecks we are destroying historical items and record,” Dr Laws says.

A battle between the previous and the long run

In 2012, after underwater cultural heritage researcher Elena Perez-Alvaro gave a chat at a convention, a physicist pulled her apart.  

“She said, ‘We are using metal that we have found underwater, some ancient lead, to do our experiments,'” Dr Perez-Alvaro says. 

While in some circumstances this lead was collected ethically, in others it was bought illegally from non-public corporations that did not comply with archaeological requirements.

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“Everything that is taken out of the water without a proper archaeological record, we will never have that information back,” she says. 

“Where the ship was coming from, where was it going. This is basic information to understand the past.” 

 Dr Perez-Alvaro sparked a heated debate when she wrote papers discussing the dilemma of using historical artefacts for physics experiments.

But even Dr Perez-Alvaro concedes there’s a case to be made for utilizing ancient lead in experiments — after it has been correctly documented and recovered. 

“We have to consider that sometimes it’s not useful to have 1,000 ingots in the warehouse of a museum.”

Searching for dark matter

The motive Dr Fiorini was so eager to get his fingers on that sunken Roman lead was to protect his experiment because it appeared for hard-to-detect phenomena — probably the most elusive of which is dark matter. 

Dark matter is believed to make up 85 per cent of the full mass of our Universe. It’s an invisible substance that does not work together with gentle however does work together with gravity. 

So whereas we won’t see it, we do have oblique proof that dark matter exists. In the Nineteen Thirties, astronomers began noticing gravitational anomalies that urged there was extra mass within the Universe than we may see.

The Swiss-American astronomer Fritz Zwicky referred to as it “dunkle materie”, or dark matter. 

It was American astronomer Vera Rubin who introduced dark matter into the mainstream within the Nineteen Seventies along with her observations of spiral galaxies. 

Since then, physicists have been trying for methods to detect dark matter instantly. Until they do, it stays hypothetical. 

“We’re building experiments on Earth looking for dark matter to interact with ordinary matter,” astroparticle physicist Theresa Fruth of the University of Sydney says.

Dr Fruth has been engaged on the LUX-ZEPLIN experiment within the US.

The chamber of the experiment is filled with liquid xenon. If a dark matter particle bumps right into a xenon atom, like billiard balls colliding, then the detector will choose up a tiny flash of sunshine.

We do not know if dark matter is able to interacting with xenon. If it does, it is a uncommon incidence.

“We’re going to run a detector, which is seven tonnes [of xenon], for 1,000 days and we expect maybe a handful of events,” Dr Fruth says. 

For these interactions to be noticed, the detector should be effectively shielded from outdoors radiation. 

Researchers in Italy are hoping to make the same remark on the Cryogenic Underground Observatory for Rare Events (CUORE) beneath the Gran Sasso mountain.

CUORE, which is Italian for “heart”, is the experiment protected by a protect of ancient Roman lead.

The ingots have been collected with the permission of cultural heritage officers, and documented earlier than being handed over to the INFN in 2010. 

Two thousand years in the past, this lead would have been used to assemble aqueducts or ammunition for troopers.

The historic significance is not misplaced on Dr Gorla.

“Something amazing is that the companies that extracted the lead from the mine stamped [their] brand on top of the bricks.”

This a part of the brick is chopped off earlier than the remaining lead is melted and moulded right into a protect. 

While the protect was being constructed, the physicists additionally measured remaining hint contaminants within the lead, uncovering vital historic info. 

He calls it a “mutual exchange” between the archaeologists who wished to know extra in regards to the historical past of Ancient Rome, and the physicists who wish to know extra in regards to the historical past of the Universe. 

The CUORE detector is saved inside dilution fridges that preserve the experiment “colder than outer space”, in accordance with Dr Gorla. 

“At this temperature, a particle passing through one of our detectors can rise the temperature enough to be able to measure it,” he says.

The level of all of that is to detect and observe the elementary particles accountable for giving our Universe construction.

CUORE began observing in 2017, and six years later, Dr Fiorini died.

The experiment he shielded with Roman lead hasn’t made any main discoveries but, however it can quickly be upgraded to CUPID — which stands for CUORE Upgrade with Particle Identification. The protect will stay in place. 

“We can easily tell that without the quality of the shield, we would not have been able to measure at the level we’re measuring now,” Dr Gorla says.

Australia may verify controversial discovering

There is one other observatory beneath the identical Gran Sasso mountain in Italy that has been the centre of controversy for many years.

Not as a result of it makes use of steel from shipwrecks, however as a result of for 20 years it has been detecting a sign the crew believes may very well be dark matter. 

Other groups have tried to duplicate the experiment, referred to as DAMA/LIBRA, with completely different strategies and have not been profitable. 

“To once and for all say, ‘Are they actually seeing something?’ We need to build a detector which is really similar,” Dr Fruth says. 

That’s the goal of the SABRE South detector in Victoria’s Stawell gold mine, which is on monitor to begin observations in early 2026, and hopefully verify if the DAMA/LIBRA sign is a real candidate for dark matter — or an error.

“It’s just this really big problem … We don’t know what 85 per cent of the matter in our Universe is made out of,” Dr Fruth says.

“Understanding that will help us understand the world a little bit better, and I like to think maybe we’ll understand our place within it a little bit better as well.”

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