The basic principles of Radioactivity-Meter
The hardware and the camera chip of the smartphone is influenced by several kinds of noise, e.g. thermal noise, electrostatic noise etc. Some are constant in time, others are growing to an upper limit when the camera is started. The radioactiv radiation (primarily gamma radiation, and to a certain extent beta radiation) changes the internal ratio and amount of noise.
Radioactivity-Meter analyzes these changes for the camera image and calculates the radiation causing these changes. Of course, noise and radiation are statistically distributed and the internal noise additionally depends on the environment, e.g. the ambient temperature, the electromagnetic radiation of the smartphone itself, the up time of the camera etc., and on the camera image and the hardware of the smartphone.
In order to get as accurat results as possible and reliable and comparable measuring values,
1.) the start conditions for each measurement should be the same as far as possible: same ambient temperature (except for zero point fixing), same temperature of the smartphone, same up time of the camera, flight mode of the smartphone switched on. Therefore Radioactivity-Meter blocks a few secondes after each measurement, before the next measurement is possible.
2. Radioactivity-Meter must be calibrated for each smartphone once, before it can be used to indicate absolute values for the radioactivity.
The most important part for the start condition of a measurement is the camera image. During the measument absolutely no incident light is allowed for the camera. Therefore the camera lens must be sealed e.g. by a black insulating tape. Of course you can keep the lens shut by your finger, but sometimes a little light shines through the fingers. In this case use at least additionally a cloth to shut the lens.
For the calibration, two values are necessary to extrapolate all other values: First fix the zero point where no radioactivity is caught by the smartphone. The zero point must be fixed at the lowest temperature of all future measurements you want to execute. Second, measure the radioactivity at a place, where the current radioactivity is known and assign this known gauge value and its unit to the value, measured by your smartphone to establish a relation between the internal hardware- and environment-dependent values of the smartphone and the real absolute quantity of radioactivity. The more exact the calibration and the higher the gauge value, the better the measurement results. From then on your Radioactivity-Meter is able to indicate the current radioactivity.
Due to the different hardware of the various smartphones we cannot ensure, that Radioactivity-Meter works on all smartphones with sufficient accuracy.