Cheap Muon Detectors Go Aloft on High-Altitude Balloon Mission

There’s something compelling about high-altitude ballooning. For not very much money, you can release a helium-filled bag and let it carry a small payload aloft, and with any luck graze the edge of space. But once you retrieve your payload package – if you ever do – and look at the pretty pictures, you’ll probably be looking for the next challenge. In that case, adding a little science with this high-altitude muon detector might be a good mission for your next flight.

[Jeremy and Jason Cope] took their inspiration for their HAB mission from our coverage of a cheap muon detector intended exactly for this kind of citizen science. Muons constantly rain down upon the Earth from space with the atmosphere absorbing some of them, so the detection rate should increase with altitude. [The Cope brothers] flew two of the detectors, to do coincidence counting to distinguish muons from background radiation, along with the usual suite of gear, like a GPS tracker and their 2016 Hackaday prize entry flight data recorder for HABs.

The payload went upstairs on a leaky balloon starting from upstate New York and covered 364 miles (586 km) while managing to get to 62,000 feet (19,000 meters) over a five-hour trip. The [Copes] recovered their package in Maine with the help of a professional tree-climber, and their data showed the expected increase in muon flux with altitude. The GoPro died early in the flight, but the surviving footage makes a nice video of the trip.

14 thoughts on “Cheap Muon Detectors Go Aloft on High-Altitude Balloon Mission

  1. So, it’s definitely a *particle* detector, but I don’t see why it’s a *muon* detector. Muon detectors have pairs of scintillators (like here), but they’ve also got a lead slab between them to absorb more ionizing particles.

    At sea level, muons dominate, but at the top of the atmosphere, they’re *totally* swamped by protons and neutrons (and electrons at the very top, but p/n still dominate over electrons as well). Obviously 19 km isn’t “the top of the atmosphere” but it’s absolutely high up enough that protons/neutrons/electrons dominate by orders and orders of magnitude. At that altitude, the muon flux is *gone* because there’s no atmosphere there to produce them.

    In fact, that’s what makes this statement wrong:

    “Muons constantly rain down upon the Earth from space with the atmosphere absorbing some of them, so the detection rate should increase with altitude.”

    Muons are *produced* by the atmosphere. They don’t come from space at all – they come from charged pion decay in interactions of protons/nuclei in the atmosphere. Muons are far too short lived to make it to Earth from any place in space. In fact, the muon detection rate *doesn’t* increase with altitude. It’s basically flat (okay, it rises a *little* up to about 10 km or so), which is how you know they’re not from space at all. (Same thing with the pion distribution). The atmosphere barely absorbs any of them.

    Now, the proton and electron distribution, both of those guys rise steadily with altitude, because they *do* come from space.

      1. Yup, that’s right. Muons are typically produced with like 1-10 GeV of energy, which (considering their rest energy of ~0.1 GeV) means they’ve got a Lorentz gamma about 10-100. Their normal lifetime is about 2 microseconds, which would limit them (at the speed of light) to 2000 feet or so, so obviously they’d never make it to ground given that they’re typically produced 10 km up or so. Time dilation (or length contraction from the muon’s point of view) stretches that to 20,000-200,000 feet, allowing them to reach ground.

        (Note that this is sometimes talked about as if it was ‘confusing’ to scientists at the time, and relativity explained it. That’s not really true, as relativity was well accepted by that point. Rossi and Hall’s experiment was actually just a measurement of the proper muon lifetime, which was unknown.)

      1. Yeah, that’s partly particle astrophysics’s fault. Solar wind particles are still called “low-energy cosmic rays,” even though they’re not “cosmic” at all. It’s just a historical thing, it’s a little bizarre. The linked article’s explanation is fine, even though the cosmic rays which generate muons are phenomenologically from an entirely different source than what cause aurorae.

        1. Hi Pat, you obviously have a lot of particle physics knowledge. I have some associates who are doing pulsed laser work and measuring 50 MeV particles which they are trying to fully characterize. Are you a particle physicist? Thanks

  2. I’ve done a few high altitude balloon flights. You can’t really trust the GoPro camera to give you a reliable view of curvature. There is too much lens distortion. The horizon may look convex or concave only seconds apart in the flight.

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