Observing Ultra-High Energy Cosmic Rays with Smartphones (2014)

Speaking of radar, many phones have FM radio receivers, which could conceivably look for radio signatures of cosmic rays. No idea to what extent the hardware is made available to software, but I just found another reason to procrastinate.

Also kudos on actually going through and doing something with this; I remember talking about using cell phone ccd's as detectors a few years ago with other grad students, but of course it never got past the chit-chat stage (I remember wanting a dosimeter in my pants to ring at me if I got too close to one of my radioactive sources).

> Theres probably 100 to 1000 or so events like that in an area the size of the Bay Area.

On what timescale?

  On a related note, when a 10^19 or 
  above event hits a densely populated 
  area, there's a decent sized ionization 
  column near the center of the shower 
  that could likely lead to cancer. 
  Theres probably 100 to 1000 or so 
  events like that in an area the size 
  of the Bay Area.

Ha! Oh man. That'd be the best alert a smart phone could ever show me.

  *beep* 
    You've just been irradiated by powerful 
    cosmic rays from outer space. Your risk 
    factor for certain forms of cancer has 
    increased by 0.013%.

I really would want to know if I was suddenly showered by cosmic rays, and my location within the crowd-sourced area-of-effect, but I wonder if an app could transmit it's sensor noise to a central server, and receive accurate results aggregated from all other app instances very quickly. I figure there'd be a lag of maybe a couple of hours or more.

Reminds me of this other site, which provides air quality stats:

https://plumelabs.com

Actually the active area of the CMOS sensor is really quite small. Like ~0.1cm^2. It is the main reason we need so darn many phones (and, as you correctly point out, an appropriate density of phones) in order to have sensitivity.

The reason it's still interesting is that at the very very highest UHECR energies, like above 10^21 eV, the density of ionizing particles is so tremendous that it's almost impossible for a (tiny) camera not to see it, if it's close to the core. This is great because unlike the Pierre Auger observatory (which is already about 100% effective at detecting showers above 10^18 eV), we become better and better at detecting events the higher the energy. So while P-A has pretty much constrained the UHE spectrum up to about 10^20 eV, the limitations on its size (as in, how much area it covers on the ground) means it can't do any better, since the higher-energy events become so rare that the probability of them happening over their patch in the desert is quite small.

The hope with CRAYFIS is that, given global coverage, we can be the most sensitive measurement of these ultra-rare events at energies above what P-A has been able to observe.

We read about them! Very cool project, especially from high-school students. A lot of people got onto this idea about the same time. See also CellRAD, which is an app that is supposed to act as a dosimiter to detect when you are near radioactive sources. It's been known for quite a while that silicon pixels can detect ionizing radiation (in fact, that's why we use pixel detectors in the inner tracker layers of state-of-the-art particle detectors such as ATLAS and CMS). The problem with the pixels in the CMOS camera of your smartphone is that they are very small (in both pitch and depth) and were optimized to respond to optical photons, rather than charged particles.

We have played around a bit with implementing these radiation-sensing features, but the main goal for the CRAYFIS project (and which sets it apart from other similar projects) is to create a distributed network of phones that all work together to act as a giant telescope for UHECR events.

Is the app open sourced? any link?

We've invited a small number of beta testers for the android platform, mostly to test that our website (which functions as our DAQ) is working and to get a baseline dataset to characterize the kind of challenges we'll have in processing the data.

AWS gave us a rather generous grant of credit for their services, and we spent a good amount of time developing a system for DAQ/live-metrics that should scale to at least a few hundred thousand users. The devices have to upload their data every ~3min, so it's a fairly significant amount of traffic. Beyond that we'd have to put either a lot more time into it or find "real" scalability experts, which means we'd need to get some $$$ first ;)

The main thing that has caused our beta rollout to stall is the fact that we have not yet been able to successfully calibrate our response to muons, which are an important component of the UHECR shower. Whereas we were able to calibrate the response to x-ray/gamma-ray photons fairly accurately using common radioactive sources, there is no easy way to generate muons under controlled circumstances (you basically need a particle accelerator). We are applying for beam time at Fermilab, so hopefully we will be able to do these measurements soon.

In parallel, we are also trying the "bottom up" approach, by developing detailed simulations to model how energetic particles interact with CMOS pixels. For this we're using GEANT, which does a great job of simulating how particle deposit energy into materials, but the hard part is modeling how that turns into actual charges that get read out by the CMOS electronics. We're getting close, but with nobody working full-time on this project and no funding, most development has happened in spurts and bursts whenever someone happens to have time away from their "day job".

In order to look for cosmic rays we have to scan HD video frames at ~30fps, which is a ton of data. So that means we have to very aggressively throw away "uninteresting" data before selecting candidates to upload to our servers (in physics jargon this is called triggering). Since the muons are not currently understood, we are afraid that we cannot design an effective trigger. Which means that if we continued the beta roll out, we might blow through all of our AWS cash and then realize retrospectively that all the data we have taken is useless. Hence we made the decision to pump the brakes on the beta testing until we can resolve the instrumental questions.

P.S.: If anyone really wants to give the app a try (unfortunately android only at the moment), feel free to shoot me an email directly. My email is my hn username at cern.ch.