Death, magic, alchemy, transmutation, poison (and so perhaps by extension, radiation) are all associated with fluorescent green to some degree. (Do a Google image search for "necromancy" or "poisonous dragon" and the majority colour is fluorescent green.) This might be partly influenced by the arsenic greens of the Victorian era.
Radiation would perhaps be better pictured with a light blue glow (Cherenkov radiation).
The green glow used in pop culture has its origin in the widespread use of radium paint to achieve a glow-in-the-dark effect (e.g. on watch faces) in the early 20th century. I still own a radium watch. The paint was always fluorescent green. And it did glow.
Isn’t it usually the phosphor that wears out rather than the radium decaying that stops them glowing? Would it be possible for someone with the correct safety equipment to apply a new layer of fluorescent paint?
