Natural radioactivity imaging

Our camera has such a good signal/noise that it can image objects using their natural radioactivity. In this case we have imaged a wallet countaining a rectangle shape of potassium salts 5cm thick. The image is done using the 1460 KeV gamma ray of Potassium 40.  

Potassium 40 is a naturally occurring isotope in potassium salts. It’s abondance is 0,011% of natural potassium. It’s period is 12 billion years. The line we use has a probability of only 11%.
This explain the low number of photons detected.

The image was done using a binocular camera at 40 cm distance.