I need electron transition detector that can respond to a dozen of photons.. so the atoms detector needs to be about just a dozen too.. I need something that can read it in an output.. what instruments is this? Geiger counter detects radiation by the click of the device.. I need something similar where the dozen atoms can click if it detect photons. I'll use it in a totally sealed dark room and an experiment. What device can I use? solar cells and bolometer won't do because they are based on electrons moving in the lattice and not from transition from excited to ground state.. what exact device or detectors (I can afford) that can detect transition from excited to ground state when it detect photons (need the sensitivity that is why I need one dozen or less atoms/photons)?