Very interesting little circuit this month in Electronic Design. Doesn't detect gammas but might be mounted near your decon/staging area to determine if there's a lot of skyshine coming through. If you saw this flicking pretty bright by the door you'd know you better spend the day inside playing cards. EMP could not burn this out, it's solid state chunky boat anchor hardware that no little zot of EMF is going to knock out.
One thing it needs is a tiny little power supply to ramp 3-12 volts to the 100 volts required and seal it up in a secure watertight case.