[Wonder Warthog]

"Learned the other day that water makes a good insulator from neutron radiation. I presume that the same will happen with ice?"

It is actually the hydrogen (protons) in the water that does the shielding. Paraffin wax, polyethylene, and similar compounds are also good neutron shielding materials.

[dhs12345]

Has to be a similar mass to a neutron. Hydrogen in water does this.