Hugh and Jim,
I was recently reading a book on nuclear reactors. I learned that iron can be used in concrete to provide neutron shielding. The iron slows the fast neutrons down to thermal levels that can be easily absorbed in the concrete. I also mine my own gold. As a byproduct of my mining, I have buckets of magnetite and hematite iron ore sand. The magnetite ore I sell to a local blacksmith for making steel. The hematite I’ve found no use for until now. I can use this black sand in place of silica sand in the concrete to provide neutron shielding for the temporary bomb shelter I’m building at my primary residence. Magnetite is Fe3O4 and is magnetic, and hematite is Fe2O3 and non-magnetic. Both comprise the black sand in the gold pan. So talk to your local gold miners about obtaining their black sands. – D.W.
JWR Replies: That is a useful idea, but perhaps it is more labor intensive than necessary. The main thing to remember about stopping the most energetic forms of radiation (neutron, x-ray, and gamma) is that the lack of quality of any particular type of shielding can be made up for with quantity. If in doubt, add thickness. With neutron radiation, it is water that is the best shielding. So damp soil works just fine. So does concrete, because it holds moisture for many years. Iron or steel actually stops gamma rays better than they do neutrons. My advice: Construct a deep shelter (my favorite is a dual purpose shelter and root cellar) with at least four feet of soil on all sides and overhead. Six feet would be great. If you live in a region with sandy soil, then the soil should be kept dampened during times of high international tensions, for the best shielding.