Fissile materials (235U, 241Am, Plutonium…) emit neutrons. Those neutrons are captured in their surrounding and emit prompt gamma rays that Temporal Compton camera detect well.
It is imposible to detect directly the weak lines of 235U (185 keV) or Plutonium which are below 300 keV with a compton camera. Anyway those lines are difficult to correctly image with coded mask cameras in realistic situations because they are screened out by shielding and often swamped in the background of diffused photons.
Here you can see an image of a punctual 241Am source inside a waste drum using « continuum neutron activation radiation » from 700 keV to 1800 keV.
The source is clearly detected and it’s punctual.
On the gamma image (only) each circle is 10°. The spot size is <10°.
The light distribution is unusual for a punctual source: the maximum light is on the edge – we see an hollow sphere because of neutron capture (probably by 1H) in the close surrounding of the Americium source.
This case demonstrates the exceptional image quality of Temporal camera.