"So you want to know about Chelovek v svintsovom kostyume? He is a rumour, a tale to tell the novobrantsy to keep them in line."
"Some say he is a scientist who got to close to an anomaly and was changed, others say he is the result of secret experiments and is looking for a cure. Others say he is a Cosmonaut exposed to radiation whose capsule crashed into the Zone."
"He is said to wander the Zone, glowing with an unearthly light."
"All say that anyone who sees him dies horribly, his touch is instant death."
"If no one ever sees him and lives to tell the tale, where do the stories come from"
The Man in the Lead Lined Suit, by Crooked Dice.
The eerie glow is Citadel Aethermatic Blue. It is not quite actinic enough for Cherenkov Radiation, which was the look I was going for.