Conversation so far:
What was the critical accident that affected Louis Slotin?
Louis Slotin accidentally began a fission reaction, which released a burst of hard radiation.
How bad was Louis Slotin's radiation injury?
Louis Slotin was rushed to the hospital.
Did Louis Slotin recover from his radiation injury?
Louis Slotin died nine days later.

Question: When did he die?
Self-contained rewrite: When did Louis Slotin die?