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This article1, among other things, claims that mobile phones can be used to detect radiation:

... the presence of scintillating pixels – white dots that flashed on and off briefly in the mobile phone videos of the explosion. The CCD imaging sensor within the camera phone is being struck by radiation thus causing a pixel to overload and appear white; in this way a mobile phone can serve double duty as a crude but effective radiation detector.

This raises two questions:

  1. Is it accurate that radiation will cause scintillating pixels?
  2. Is there anything else that can cause scintillating pixels, especially related to videoing explosions?

1. The article is attempting to show that the TianJin explosion was a nuclear explosion. Their "evidence" seems quite dubious.

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    Everything recorded in a mobile phone camera is "radiation". There would be no picture at all if that wasn't true. If the claim is that the detectors can also detect ionising radiation (like gamma rays, fast electrons, alpha particles etc.) that might be interesting. But a CCD camera isn't designed to tell the difference between a bright flash of visible photons, a gamma ray or an electronic glitch, so "white spots" are not going to be strong evidence of anything. – matt_black Aug 27 '15 at 19:28
  • @matt_black the context is a nuclear explosion, so yes, they're talking about harmful ionizing radiation. Also, there is a seemingly plausible mechanism - ionizing radiation is higher energy, which could cause a CCD pixel "to overload and appear white". – Rob Watts Aug 27 '15 at 20:33
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    The article then goes on to "explain" why there weren't such artifacts on the cameras: "This was NOT an accident, the fracture pattern around the crater proves a to be a shallow sub ground burst. If it was a sub ground burst, then a small nuclear weapon is the biggest possibility because once a nuke has to push dirt, the blinding flash will not be seen. A slightly subsurface detonation would explain why camera sensors did not get strange artefacts." Whole thing is self-contradictory mess. – vartec Aug 28 '15 at 1:03
  • @vartec Yeah, that's why I focused on this one piece rather than the overall claim. There's no real credibility for the explosion being nuclear. – Rob Watts Aug 28 '15 at 14:40
  • You might be interested in some of the DIY geiger counter projects out there that repurpose digital camera sensors for that task. – PlasmaHH Sep 30 '15 at 13:24
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Plausible

Not a scientific paper, but Q&A from Health Physics Society describes experiment with disassembled CCD and CMOS sensors.

[...] it is true that both the charge-coupled silicon devices and the metal-oxide semiconductors may produce visible light scintillations in response to ionizing radiation. Just as visible light will set free electrons through photoelectric interactions in silicon, higher-energy radiations such as alpha, beta, and gamma radiation also have the ability to free electrons in the material. The subsequent light emission normally occurs when free electrons combine with the holes that represent the positive charge carriers; this recombination process sometimes results in the emission of energy as visible light photons. In silicon the process is relatively inefficient so that relatively few of the ionization events that set free electrons lead to light emission. If the frequency and density of recombination events is sufficiently high, however, some of the light pulses may be sufficiently intense to be visible to the naked eye, especially in a darkened environment.

But before going any further, reasons why in the case of Tianjin explosion footage it cannot be alpha radiation: Detecting it requires disassembled camera, because optics in front of sensor would block alpha radiation. On top of that, alpha has very low penetration, even few centimeters of air is enough to stop it, so it wouldn't even reach camera in the first place.

That being said, there is still possibility for very strong beta & gamma radiations (as nuclear explosion would produce) to interact with CCD/CMOS sensor enclosed in fully assembled camera:

The situation is quite different for beta and gamma radiation. The maximum energy beta radiation from 40K is about 1.3 MeV, and the approximate distance such a beta particle could travel in silicon is about 3 mm, a dimension much greater than the thickness of the active material in a CCD or CMOS. The average beta particle traversing the same 20 micron path length as the alpha particle would produce approximately 5,000 to 10,000 ionization events. Thus, the ionization density, as well as the total ionization per particle, would be much less for the beta radiation than for the alpha particle. This makes it much less likely that one would be able to see the light emission with the naked eye. There are optical microscopy enhancement techniques that might make these weaker scintillations visible.

Gamma rays will also interact in silicon to set free electrons that may lead to recombination and light emission, but the situation with respect to the gamma radiation is even more restrictive as regards the possibility of viewing the light emission. The probability that a 60 keV gamma ray will interact within a 20 micron thickness of silicon is about 1.4 x 10-3. This compares to the probability of 1.0 for the alpha particle (and the beta particle). Additionally, the photon energy is much less than the alpha or beta energy and only about half of the photon energy, on average, would be deposited in the silicon per interaction. Thus, one would have an even more difficult time trying to visualize light emissions from gamma-ray interactions.

On the other hand, keep in mind that such experiments talk about detecting scintillations on images, that are very dark.

  • What's the scale of radiation tested here vs. what you might expect from a nuclear explosion? – Rob Watts Aug 28 '15 at 19:30
  • Also of note: eric.ed.gov/?id=EJ900150 This is not scintilation detection, but detection of direct energy deposition by ionizing charged particles (mainly muons). – dmckee Aug 29 '15 at 0:58

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