Muons and Archaeology

NARRATOR: Listen to part of a lecture in an archaeology class.

<-FEMALE PROFESSOR:-> A popular misconception about archaeology: Some people imagine we just go out into the field with a shovel and start digging, hoping to find something significant.Well, while there is an element of luck involved, we have an array of high-tech tools to help us figure out where to concentrate our efforts.One of the newer tools actually relies on particle physics.Talk about interdisciplinary! Here’s a machine that brings together two very different sciences.

This machine is called a muon detector. Muons are subatomic particles that result from cosmic rays….OK, let me start over. Cosmic rays aren’t actually “rays”—they’re basically protons, zipping through outer space at close to light speed.And when they collide with the atoms in Earth’s atmosphere, they break up into smaller particles—muons.Now, these muons are still highly energized, so they can easily pass on down to the Earth’s surface.In fact, they can pass through solid matter, so they can also penetrate deep into the surface.And it’s this property of muons that archaeologists are taking advantage of.

Let me explain. With the right kind of equipment, scientists can use muons to createa-a-a kind of picture of the structures they’re studying.Let’s say we’re studying a Mayan pyramid in Central America, and we’re interested in finding out if there are burial chambers or other rooms inside.Well, a muon detector will show a greater number of muons passing through the less dense areas inside the pyramid.Yes, Andrew?

<-MALE STUDENT:-> Um, I’m not sure I get how this muon detector works exactly…

FEMALE PROFESSOR: Well, muons lose energy as they pass through dense material, like the stone walls of a Mayan pyramid.So, more muons, and more energetic muons, will be passing through empty spaces.The muon detector can differentiate the areas where more muons are passing through—the empty spaces—as well as where there are fewer muons—the walls and dense areas.These empty spaces will show up as darker.So we wind up with a-a kind of picture of the pyramid, and its internal structure.

MALE STUDENT: A picture?

FEMALE PROFESSOR: Sort of like an x-ray image.

MALE STUDENT: OK, so if we see darker areas inside the pyramid, we assume it’s an empty space with more muons.

<-FEMALE PROFESSOR:-> Exactly. With this technology, we can see what’s inside a structure before we dig.So we know exactly where to explore, and we can minimize the damage excavation can cause—even a little damage could result in our losing vital information forever.Now, muon detectors have been around for some time, but they’ve been improved upon since archaeologists started using them.

In 1967, a physicist placed a muon detector beneath the base of one of the Egyptian pyramids at Giza.And he was looking for burial chambers.Now, it happened that the muon detector found none, but he did demonstrate that the technique worked.Unfortunately, the machine he used was so big that many archaeologists doubted muon detection could be practical.

How could they get a massive piece of equipment into, say, uh, the jungles of Belize?Then there was the issue of range.The machine used in 1967 could only scan for muons directly above it, not from the sides, so it actually had to be put underneath the pyramid so it could look up.That meant, if you wanted to find out what was inside an ancient structure, you’d first have to bury the detector beneath it.

There’s been a lot of work on these machines since then, and these problems have been solved by and large.That’s not to say the technology is perfect.It-it would be nice, for example, to have a system that didn’t take six months to produce an image.I suppose that’s better than the year it took for the 1967 study to get results, but still ….Well, there’s good reason to believe that with better equipment, we’re going to see muon detectors used much more frequently.They’re already being used in other areas of science—uh, for example Japanese scientists studying the interiors of volcanoes—and there are plenty of archaeologists who would love to use this technology.