IceCube's construction finished in 2011, built out to a full cubic kilometer of detectors buried in Antarctic ice. Because the South Pole site only allows construction during the six-month summer season, the observatory was built one borehole at a time. The array is placed deep underground because light cannot travel far through surface ice or air, and it spans such a large volume because the astrophysical neutrinos it hunts are extremely rare, so a bigger target improves the odds of a detection and helps reconstruct the direction a neutrino came from. The detectors themselves are pressure-resistant glass spheres packed with photomultiplier tubes, arranged in strings, with a densely instrumented central region called DeepCore.
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The hosts compare the string of sensors to a long row of ski-ball balls to illustrate how photomultiplier tubes are packed one after another down each borehole.
452 words · auto-generated from the episode video
42:21They say, all right, we're gonna give you a lot of money now in order for you to make the IceCube project. Construction completes in 2011. IceCube is now a cubic kilometer worth of detectors. The building that everyone sees, right? That's the tiny dot at the very top. This is such a massive infrastructure project. It's like really actually hard to, especially in an environment that's not very conducive. No, it's in Antarctica. They're building this thing in Antarctica. That means that their construction timeline is only six months. Right, because you can't do that. Because you can't go in the winter to construct because everything's dark, right?
43:03So you have to go in the summer and you have to try and construct this thing. They did it one at a time, you know? One borehole at a time. Slowly but surely, they started getting this thing together. And just to reiterate, the point of why is it so deep and why is it so wide? It's so deep because we can't detect these extra galactic, highly energetic neutrinos too close to the surface. Yeah, we can't detect any neutrinos close to the surface because light just, it starts and ends, starts and ends. So if I'm trying to detect light from like a meter or two meters away-- Even if it happened over there, it wouldn't even, the light would never make it to your-- Yeah, it would just like interact with the air and then you're done.
43:45And then the reason it needs to have such this large area is because the thing we're looking for, the extra galactic, high energy stuff is so infrequent. We need to create the biggest target possible and hope we get lucky. And hope we get lucky. The other thing for why it can be this big is that if we do catch it, we can really track the whole thing. And then we have a good idea about what direction it came from. It's absolutely incredible. What they've been able to do. And this is what a detector looks like. These are the photomultiplier tube type thingies that go in.
44:27This is called the deep core detector. It's a densely instrumented set of photomultiplier tubes. It's a fancy CCD. Yeah right. And there's a bunch of these all the way up and down into the thing. Okay. Like just like, so it's basically like a ski ball when you have all the balls next to each other. It's just like a long ski ball thing. Yeah yeah. It's a pressure resistant glass sphere because you gotta get down to really high pressure. It's got a bunch of electronics and it's absolutely amazing.