Sub-atomic Particles Used To Map Pyramid

firegate writes "Yahoo News is reporting on a pyramid-mapping project focusing on an ancient Aztec site in Teotihuacan, Mexico. Scientists are attempting to map an ancient pyramid by detecting muons - sub-atomic particles which are left as remnants of ancient cosmic rays. A similar method was used to scan Egypt's Khephren Pyramid in the 1960's."

Comments

Re:So how does it work, exactly?

[Anonymous Coward]

It detects the amount of shielding that the walls provide. I = I_0 * 10 ^ (- x/ x_1/10), where I is the intensity measured, I_0 is the unshielded intensity, x is the thickness of material, and x_1/10 is the tenth thickness of attenuation for that material (i.e. the amount of material required for the intensity to drop to 1/10 of its original value). All they have to do is solve for x. Obviously, if x drops somewhere there is 'missing' shielding.

Useful resources on this technique

[thesp]

This was on my Physics undergraduate course; a rather nice technique. Releated resources from my lecture notes give:

An abstract, a presentation on applying similar techniques to volcanoes, a citation [L. Alvarez et al, Science 167, 832 (1970)] (accessible only to subscribers of Science, I'm afraid), a Physics Today article, a useful paper.

is the conference where the experiment was originally proposed.

Teotihuacan is not Aztec

[T-Punkt]

It's even mentioned in the article the editor cites. *sigh*

The culture of Teotihuacan predates the Aztecs by a few hundred years. It climaxed around 500, went under around 600 (my sources say 700). The so-called Aztecs arived around 1200 and gave the site its name, but that's the only Aztec connection to Teotihuacan.

Re:Teotihuacan is not Aztec

[ParticleGirl]

So they a) lived there and b) gave the place its name. Seems like a good enough pair of reasons to call it an "Aztec site" to me. Would you prefer "mysterious Teotihuacan culture" on all references?

Actually, they didn't live there. They lived nearby, and considered the enormous ruins a holy site. They thought that that city was where humans came into being ("Teotihuacan" means "City of the Gods" in the Aztec language, Nahuatl.) In the literature, it really is referred to as a Mysterious Teotihuacan Culture (also called "Toltec" because this is what the Aztec called the Mysterious Teotihuacano Culture.) They had an enormous empire, conquering and trading with groups as far as 1500 km to the south, and Teotihuacan was the FIRST major urban center in the New World. It was enormous, with big, government-issue apartment complexes, sewage systems, and public market places.

Aztecs thought it a high compliment to be considered Toltec-ish, since when they established themselves in the area a thousand years after the place had peaked they claimed legitimacy by claiming to be at least the spiritual descendents of the Toltec (hey, look, they were fierce warriors and so are we!) even though they and everyone else acknowledged that they were entirely different peoples.

And this really is just about the extent of what we do know about the truly Mysterious Teotihuacano Culture (with some other random speculations about how they came to be the only big culture in the New World without someone like a king, how and why the city of hundreds of thousands came to be burned to the ground and abandoned within about 50 years, et cetera.) We know a hell of a lot about the Aztec. They were separated by time, space and culture. Saying 'what's the difference' between Aztec and Teotihuacano is like saying 'what's the difference' between you and an Ancient Greek.

The article is written by a scientific illiterate

[Tau Zero]

Anybody able to discern useful details?

You'll get few from that article, unfortunately. For instance, the muons come from the collision of cosmic rays with nuclei high in the atmosphere; some of the resulting particles are pions, which decay to muons on the way down. But the author (or editor, in some idiotic attempt to make the article more "accessible") completely misled his readers by writing nonsense such as

Remnants of space dust that constantly showers the world....

when "space dust" has nothing to do with it, and

Since there are fewer muons in an empty space than in solid rock or earth...

which has no relation to reality that I can see.

The system works a lot like a CAT scanner, where the absorption of penetrating radiation is measured over a variety of different paths through the object to be scanned. The only real difference is that the radiation is muons rather than X-rays (less easily absorbed, thus able to provide detectable signals through a hundred meters of rock - you should see what Fermilab uses to absorb muons so they can do neutrino experiments) and the source is natural. If you had enough money you could make your own muon source and scan the thing yourself, but when nature has been so obliging there's really no great need.

Muons

[yet another coward]

Muons are created high above the earth when cosmic rays interact with matter up there. They shoot out from those reactions at velocities near light speed. Because they are traveling at such high velocities, their lifetimes are extended as predicted by special relativity. Instead of nearly all decaying within a tiny fraction of a second, many of the muons exist long enough to travel down and reach us. They are a few seconds old--I think it is a few seconds; it might be less--when they reach us. They pass through objects on the surface of the earth at about the rate 1 / second / cm^2.

Muons can react with matter, but such interaction is very unlikely. If the matter is denser, such as stone, they are more likely to interact. By placing detectors inside the pyramid and counting muons coming from overhead for a long time, the scientists can estimate how much matter. They have another estimate of the matter is there by comparing to the number they would expect if they had passed through air. If that experimental estimate of the matter present is somewhat less than the expected amount based on the thickness and density of the pyramid above the detector and the density of the stone, there much be less stone than expected, possibly due to a secret chamber.

Re:So how does it work, exactly?

[Anonymous Coward]

The author of the story was misleading. Muons are created in the atmosphere in high energy cosmic ray to atmosphere interactions. While the equation looks like a decay rate equation, that is not the case. If (- x / x_(1/10) ) were replaced by ( - t / t _(1/10) ) (normally shown as t_(1/2), but there is no reason you can't measure tenth-lives vice half-lives) it would be *a* decay rate equation. The shielding eqaution has a similar concept (exponential decay), so it takes a similar form. Everything has a tenth-thickness of attenuation to a different degree for different types of radiation (for example an opaque substance will have an almost zero tenth thickness for some frequencies, but a window will have a very large tenth thickness for some frequencies).

Similar project at UT

[apirkle]

There's a similar project at the University of Texas at Austin. It aims to image Mayan pyramids in Belize.

They have a fairly sparse website, but there's a quite good PDF of a slides from a talk that Roy Schwitters (former director of the Superconducting Supercollider) gave.

Re:Replacement for the X-Ray machine?

[dtl]

Well to scan in a reasonable time, say 10 sec or less you would need much more than the background level of muons from cosmic rays.

Generating muons would require a particle accelerator. This is already pushing the cost beyond that of standard x-ray gear.

Then you have to consider the interaction of muons with the human body. They are penetrating ionizing radiation, and they decay into more fast ionizing particles once they are inside the body. Not something you really want.

Best to stick with metal detectors at airports I think.