Yeah I think I explained it badly. They sorta stream through the detector until they interact, and then potentially undergo multiple compton scatters or photoel

Yeah I think I explained it badly. They sorta stream through the detector until they interact, and then potentially undergo multiple compton scatters or photoelectric absorption (or other weird stuff) that produce secondary particles that actually excite a region around the discrete interactions and those excited atoms are what produces the observable signal. Then (at least for a scintillator) the atoms that got excited relax and release a flash of light with a characteristic decay time that is the main limit on how precisely you can resolve individual gammas. Semiconductors are kinda similar but dislodging electron-hole pairs; the higher mobility of these pairs is why the resolution is so much tighter. Imaging detectors have more electronics attached, e.g. two photomultipliers at each end or pixellated photomultipliers, and timing analysis of these pulses is how you get position. Things like a full energy deposition peaks happen when the gamma ray dies in the detector, but it doesn't necessarily dump its energy all in one spot. Since you have to wait for all the excited atoms to decay or the total charge from electron-hole pairs to be collected you have to integrate the total amount of light/charge over some window to get the total energy deposited. Sometimes they escape out the other side and take some of their remaining energy with them, which causes some distinct features in the spectrum too. The timing and electronics for doing position sensing of the gamma path through the detector (i.e., what you need to reconstruct an image) are... complex. Dead time and false correlates (e.g. another gamma in the detector at the same time, aka false coincidences) are a thing and they are factors that contribute to uncertainties. There's a bunch of statistical analysis you have to do to try and correct for these effects and pull the signal out of the noise. In a Compton camera, you can correlate the first scatter's trajectory back into a cone of possible incident directions, which you then stack up to form a picture. Hence why I said the image you get out is very blobby and more like a heat map than an image. But you pay a price in efficiency, as you can only count some fraction of the actual interactions in the detector now. I'm a bit rusty on the really nuts and bolts details, I don't work with this type of detector anymore. We mostly try to avoid using this type of detector for our localization, because they are crazy expensive and complex.