The best way I can think of to make a "radiation camera" is similar to how you can make a "wifi camera", by hooking up a radiation detector to a pan-tilt mechanism, and moving it around very slowly and sampling the amount of radiation detected at each point. Essentially a single pixel "camera" that you have to move around to take a full picture. However, you'd also have to shield the detector from any radioactivity coming from directions that it's not pointed in, which is especially hard if you're trying to capture gamma rays, since they like to penetrate through everything. Its like if light could leak into the side of a normal camera, you'd get rubbish photos
Sure, we probably can't make Geiger counters in a form factor that allows an array of a million of them in a handheld device, but maybe 20x16 or something?
https://www.cosmos.esa.int/web/xmm-newton/technical-details-...
For instance we routinely take plenty of x-ray images, though there is fortunately not a lot of stuff just lying around that are bright enough x-ray sources to properly expose standard x-ray detectors.
Detecting electrons or protons (beta and alpha radiation) in such a way that you can work out their arrival direction is also doable, but the equipment is fairly bulky and you tend to have to wait a long time to accumulate enough detections to see anything.
However that might not work well because the material around the pin-point aperture might not absorb sufficiently the rays coming from different directions and it cannot be made thick.
So what may work better is to make the detector array in the form of a compound arthropod eye, where each detector is at the bottom of a long tube whose walls absorb the rays coming from any other direction except its axis.
In practice, besides trying to absorb the rays coming from different directions, preventing them to reach the detector, for high-energy rays there is the alternative to use 2 or more collinear detectors for each direction (corresponding to an image pixel). A high-energy particle or photon will pass through all collinear detectors, causing simultaneous pulses at their outputs. Whenever such pulses are not simultaneous, they are discarded, because they correspond to rays coming from another direction than intended for that pixel. The accumulated count of filtered pulses per some time interval will give the luminosity of the corresponding image pixel.