Cosmic rays aren't neutrons, they mostly electrons or muons (and maybe gamma rays). For stopping gamma rays and electrons, 10 feet of water or dirt is a fine fo

Cosmic rays aren't neutrons, they mostly electrons or muons (and maybe gamma rays). For stopping gamma rays and electrons, 10 feet of water or dirt is a fine for stopping them. So is about 7 feet of concrete, 2 feet of steel or one foot of lead. So is making sure you are closer to sea level. Muons will pass through all of those fairly easily but the flux isn't that high. You might have a few events per year where the flux is high.