  The CMOS camera found in many cellphones is sensitive to ionized electrons.
Gamma rays penetrate into the phone and produce ionized electrons that are then
detected by the camera. Thermal noise and other noise needs to be removed on
the phone, which requires an algorithm that has relatively low memory and
computational requirements. The continuous high-delta algorithm described fits
those requirements. Only a small fraction of the energy of even the electron is
deposited in the camera sensor, so direct methods of measuring the energy
cannot be used. The fraction of groups of lit up pixels that are lines is
correlated with the energy of the gamma rays. This correlation under certain
conditions allows limited low resolution energy resolution to be performed.
