Cladding would degrade. But a large diameter glass rod would be fine. There are a lot of options, including a scanning the light source combined with a non imag

Cladding would degrade. But a large diameter glass rod would be fine. There are a lot of options, including a scanning the light source combined with a non imaging sensor. Or you could put a scintillating detector in a lead ball with a hole, and scan by rotation and pipe the light from the scintillator out to external electronics. All you need is a long pipe installed to get started.