Beam solves the 'case of the gold'

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By Roger Snodgrass

Several valuable nuggets have been locked in a safe every night at Los Alamos National Laboratory lately, and that isn’t a reference to weapons codes or nuclear secrets.

A New Mexico State University neutron physicist working with a geologist from Ohio has kept some precious pieces of raw gold in the vault at the Lujan Neutron Scattering Center.

That’s where they are secured when Heinz Nakotte is not actually peering inside one or another to see how it’s made.

Nakotte took a couple of examples out of the safe Thursday to demonstrate what he called “the big question.”

Could neutrons help geologists, natural history curators, investors and collectors tell the difference between conventional gold nuggets and what turns out to be a super class of gold, known as single-crystal gold?

Crystalline gold is not valued by weight alone, but also by its shape and appearance. There is a big difference, it turns out, as much as 10 times the value, between gold grown from a single crystal and ordinary gold.

“This is a perfect single crystal,” Heinz said, pointing to a pyramid shaped piece with inward glittering folds on one of the sides. “The edges are well formed but the faces are not fully developed.”

Then he demonstrated another piece, somewhat duller, but more regular and seemingly embossed with a cross on top. Hard to see by the eye alone, it was too good to be true.

“It came from Russia,” he said. “They even cast some quartz on there to have some impurities, so it looks more naturally grown.”

Nakotte said the owner paid $70,000 for two of them and, needless to say, he was not happy to learn what the lie-detecting neutron beam revealed.

By using the non-invasive properties of neutrons, subatomic particles that are normally found inside the nucleus of an atom, Nakotte had penetrated the outer layers of a piece of gold and developed a kind of picture of what the inside looks like, without having to crack it open.

Neutron scattering can be used to study the interior properties of solids and liquids.

Neutron particles are beamed into the specimen where they activate the nucleus of these gold atoms and bounce out, carrying recognizable signatures for the properties of those atoms.

X-rays, which are sometimes used to assess gold qualities only see the outer layers.

Cracking open or damaging nuggets worth tens and hundreds of thousands of dollars is not advised.

Some of the pieces that have been under investigation are listed on the Stack’s website, www.stacks.com, a company that auctions rare coins and other valuables.

The project collaborator, John Rakoban, from Miami University of Ohio, has a paper on the recent neutron detective work in Los Alamos, soon to be published in Rocks and Minerals magazine, which happens to have a cover story on gold specimens this month.

Alan Hurd is the group leader for the Lujan Center, a user facility that hosts scientific experiments from all over the world.

He said the gold study has a good scientific rationale, besides all the glamour, including information on magnetic structures and phase transition as seen in crystal growth, not to mention exploring the capabilities of a recently acquired instrument.

“Clearly samples like these gold specimens come from some extreme environment in a geological setting,” he said, noting that the lab’s future signature research facility, MaRIE also has as one of its purposes the study of materials under extreme conditions.

Nakotte, heads the Magnetic Materials Program of New Mexico State University and spends every other week at the Lujan Neutron Scattering Center at Los Alamos National Laboratory teaching students and conducting experiments.

He said that four of the six single-crystal pieces under investigation came from a riverbed in Venezuela on the border of Brazil in the Roraima Shield District of Icabar.

Not to encourage a gold rush, he quickly added that a robber had killed the person who found one of the pieces.