It was probably an imaging radiation detector regardless, the spinny bit would likely be some sort of camera to add context to the radiation image.

Imaging detectors can get a lot fancier than just two planes. One design is basically segmented crystals and you look at the timing between the separate segments light up as a gamma ray passes through each quadrant. You can then work backwards from those sub nanosecond time difference to get the direction, and stack up a bunch of events to make a sort of picture (more like a blobby heat map).

For neutrons there is an even crazier imaging technique called a coded aperture that I won't even try to describe here. Suffice to say it's very clever and unintuitive.

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defrost an hour ago | parent [-]

Ha - my mental model was to spin a partial shield about a crystal and watch the incoming counts and timings - dipping when shield passes between source and crystal, increasing on the gap transit.

With a few tweaks.

> the separate segments light up as a gamma ray passes through each quadrant.

Err, one single ray (we doing wave fronts or particles in our slit experiment here) surely only impacts and flashes once in one segment .. or passes through with no impact?

A whiteboard might be easier for this convo, or perhaps we let it rest. Coded aperture looks to be more or less as I imagined: https://www.sciencedirect.com/science/article/pii/S135044871...

	▲	gh02t 34 minutes ago \| parent [-]
		Spinning shield is a thought people have had but it doesn't work very well in practice (for gamma imaging). Usually you want to avoid anything that blocks gammas as much as possible because you need every one you can get. I wanted to try spinning one of the scintillator logs we used, which is more or less the same idea, but it isn't practical either for a bunch of reasons. Gammas tend to act more like particles in the detector. They don't stop all at once, they tend interact multiple times and deposit their energy in multiple places along a line via a ton of different physical interactions. My description was simplifying and conflating things a bit, you can look up optically segmented detectors, as well as Compton scatter cameras if you want a better answer. There are other imaging approaches, too.