If you have never heard of an app called GammaPix, don't worry, most people haven't. However in scientific circles, the app did quite a round last year, when it alleged that smartphone cameras could detect gamma rays. The GammaPix app alleged that it would enable your smartphone to be used as a low resolution Geiger counter. The app was tested at the Disaster City facility in Texas last year.
The latest news coming out of the Idaho National Labs seemingly gives credence to the claim that our smartphone cameras are indeed smarter than we have been giving them credit for. A group of researchers at the Idaho National Labs had tested the idea behind this claim and provided credence to the science behind it.
The idea is simple, the CMOS sensor in a camera module captures photons (light particles – FYI though light is both a particle and a wave), which the software on the smartphone then converts into the photos we see in our gallery. The CMOS sensor should also be able to generate some sort of signal in the presence of radiation, all that is required is an app capable of translating what the CMOS sensor "sees" into an image or counter, which would effectively convert a smartphone into a Geiger counter.
For those who are more scientifically inclined, once a photon particle strikes the CMOS sensor of a camera, an electron gets pushed out of the semiconductor and an electron-hole pair is created, which is then captured by the camera's electronics. Different colors reflect light with different wavelengths, which basically means that photon particles striking the CMOS (Complementary Metal Oxide Semiconductor) sensor have different energies (measured in eV – electron volts and is usually less than 3.1 eV). The semiconductor then reads the accumulated charge (caused by the formation of electron-hole pairs) of each cell in the image and the software component produces the picture on the screen.
The research team, led by Joshua Cogliati, studied the same effect – this time albeit with gamma radiation instead of visible light and also created an app to do the software enhancements and readings. Since gamma radiation is a much higher energy than visible light, the electrons energized by it get complete knocked out of the semiconductor material. Not only that, on their way out they may also ionize secondary electrons. According to Joshua Cogliati, "a 20 keV electron might ionize 10,000 secondary electrons. Electrons with high enough energies will leave trails of ionization as they travel through the material." These trails are detectable, and here is where their app comes into play.
Instead of testing GammaPix, Cogliati's team coded their own app – CellRad. The CellRad app was designed on the Android platform and was run on a Samsung Nexus S, a Galaxy Nexus, a Samsung Galaxy SIII and the LG Nexus 4. The primary cameras of these devices was used in lieu of the secondary camera as higher the resolution, the better the chances of detection. CellRad was tested using radioactive isotopes of Selenium, Iridium, Cesium, Cobalt and Americium.
Incidentally, it was the older Nexus S which beat the remaining test handsets out of the park, in terms of radiation detection per image. The Samsung Galaxy S III lost due to "excessive noise" or false positives. The researchers also stated that both the Nexus devices came much closer to each other in performance as compared to the other devices. The older Nexus S still packs a punch, no wonder NASA sent it into space.
However Cogliati has warned that in their present avatar, smartphone cameras cannot match up to the reliability and performance of an actual Geiger counter. However as the team states, "but there are many more cellphones around than high-quality radiation detectors, which means there are times when the cellphone can be the best detector available." Cogliati's team has published their findings at Arxiv and you should head over there if you want to read more on this.
On our part, we are content with the way our cameras work, and it doesn't seem for now that "Geiger Counter" would be featured as a smartphone specification. However, would you like your smartphone to work as a Geiger counter, apart from the multitude things it already does? Do let us know in the comments below.