Natural radioactivity imaging

Our camera has such a good Signal/noise that it can image objects using their natural radioactivity.
Here is an image of a plate of standard glass done with a pose of one day
This view is done using the gamma lines from Actinium 228 from Thorium 232 decay chain. Thorium is an impurity in sand.

The second image is done using the 1460 KeV gamma ray of Potassium 40.
Potassium is present in glass at a few tenth of a percent.
Potassium 40 is a naturally occurring isotope. I’s abondance is 0,011%. 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.