Ok so the thing about radiation is that it's hot.
Like there was an incident with an orphan source where 3 men found this piece of iron that was warm and used it as a heater. Stayed around it all night for warmth and carried it on their back. All three got really bad radiation burns from it and were often in and out of the hospital. At least one of them died.
(And if an orphan source is glowing, you're fucked. You need to throw that thing as far away from you as you can and fucking run. Your hand may not survive but you might.)
Onto Iron Lung: you remember how Simon was complaining about how hot it was in the ship? Do you remember how long he was in there for? How many pictures he took? How many times he used the camera for light?
He was never coming out unscathed.