[beebmam]

Lead does not block "all radiation". Here's a great video that explains common types of radiation and what kind of materials are effective at blocking each of these types of radiation: https://www.youtube.com/watch?v=iTb_KRG6LXo

There's plenty of radiation that we have no effective way of blocking, like neutrino radiation.

[formerly_proven]

Ability to block/attenuate radiation is proportional to interaction probability which is generally also proportional to biomedical risk: ergo, if we can't block it, we don't care about it.

[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?