[hinkley]

Short version: sometimes it's not the bullet that kills you but the spray or ricochet. There are plenty of types of radiation that you want to block with light elements. If a high energy particle spalls off some hydrogen atoms, then those can be less damaging than a similar collision in steel or lead. Fungi is a mixture of mostly light elements.

But that's about the extent of my knowledge.

Do you happen to know if in a composite shielding situation (several layers of multiple materials) would you put the lead on the outside facing the hard radiation, or on the inside?