OFFICIAL54 What aspect of muons is most useful to archaeologists?

[00:01.51]NARRATOR: Listen to part of a lecture in an archaeology class.
[00:06.23]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.
[00:16.77]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.
[00:25.29]One of the newer tools actually relies on particle physics. Talk about interdisciplinary!
[00:32.05]Here's a machine that brings together two very different sciences.[00:37.17]This machine is called a muon detector.
[00:40.50]Muons are subatomic particles that result from cosmic rays….
[00:45.77]OK, let me start over. [00:48.93]Cosmic rays aren't actually "rays"—[00:52.09]they're basically protons, zipping through outer space at close to light speed. [00:57.16]And when they collide with the atoms in Earth's atmosphere, they break up into smaller particles—muons.
[01:04.55]Now, these muons are still highly energized, so they can easily pass on down to the Earth's surface. [01:11.72]In fact, they can pass through solid matter, so they can also penetrate deep into the surface. [01:19.25]And it's this property of muons that archaeologists are taking advantage of.[01:24.97]Let me explain. With the right kind of equipment, scientists can use muons to create a-a-a kind of picture of the structures they're studying.
[01:35.67]Let's say we're studying a Mayan pyramid in Central America, [01:39.86]and we're interested in finding out if there are burial chambers or other rooms inside. [01:46.33]Well, a muon detector will show a greater number of muons passing through the less dense areas inside the pyramid. 
[01:55.84]Yes, Andrew?
[01:57.16]MALE STUDENT: Um, I'm not sure I get how this muon detector works exactly…[02:01.89]FEMALE PROFESSOR: Well, muons lose energy as they pass through dense material, like the stone walls of a Mayan pyramid. [02:10.04]So, more muons, and more energetic muons, will be passing through empty spaces. [02:16.19]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.
[02:29.83]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.
[02:40.31]MALE STUDENT: A picture?[02:41.18]FEMALE PROFESSOR: Sort of like an x-ray image.[02:44.20]MALE STUDENT: OK, so if we see darker areas inside the pyramid, we assume it's an empty space with more muons.
[02:51.60]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—
[03:05.75]even a little damage could result in our losing vital information forever.
[03:10.04]Now, muon detectors have been around for some time, but they've been improved upon since archaeologists started using them.
[03:17.89]In 1967, a physicist placed a muon detector beneath the base of one of the Egyptian pyramids at Giza. [03:26.10]And he was looking for burial chambers. [03:28.67]Now, it happened that the muon detector found none, [03:32.68]but he did demonstrate that the technique worked.
[03:37.10]Unfortunately, the machine he used was so big that many archaeologists doubted muon detection could be practical. [03:44.64]How could they get a massive piece of equipment into, say, uh, the jungles of Belize?
[03:49.72]Then there was the issue of range.
[03:52.88]The machine used in 1967 could only scan for muons directly above it, not from the sides, [03:59.63]so it actually had to be put underneath the pyramid so it could look up. [04:05.00]That meant, if you wanted to find out what was inside an ancient structure, you'd first have to bury the detector beneath it.[04:13.21]There's been a lot of work on these machines since then, [04:16.21]and these problems have been solved by and large. [04:19.20]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. [04:26.77]I suppose that's better than the year it took for the 1967 study to get results,
[04:31.97] but still …. Well, there's good reason to believe that with better equipment, we're going to see muon detectors used much more frequently. [04:40.77]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.