You need one of the iDevices or Android devices with camera.
Also you need a sticker to cover the device camera. We used two types of stickers with similar results. One is aluminum foil sticker (Avery Dennison, 6007, available from Office Depot, shaped as a five-ray star, with several colors on each sheet). Its advantage is that it is completely opaque, but on the other hand it provides additional shielding from radiation because it contains aluminum foil layer.
The other sticker we tried is Avery 5459, round ¾” black paper Color Coding Label available from Office Depot website. Some masking tapes may work too and they will give similar results. The more opaque – the better, yet it has to be preferably non-metallic and as thin as possible.
Finally, note that covering camera with your finger usually doesn’t work: fingers are surprisingly transparent to light.
- Cover the device camera with one of the recommended stickers. Make sure that sticker is not letting any light in by checking camera feed on the screen. Working in darker environment helps to detect and block stray light.
- Bring the device camera as close to the sample as possible. (Remember, there is an inverse squared distance law for point like-source in vacuum. In air and other substances the signal weakens even more, depending on the energy of the particles.)
- Run the app. It will take a series of exposures. The app will reject frames if there was too much visible light detected. The output will be given in approximate multiples of normal background radiation. Hence the readings 1.0 mean “normal” level of radiation. Please remember that this number is only a ballpark estimate and there may be significant radiation not detected by the app.
Start with short exposure times to get an idea about how long it takes to process the data on your device. For higher accuracy and sensitivity you can increase exposure time in the application settings.