The current estimate for how much shielding is needed for a long-term habitat on the Moon is a minimum of 700 g/cm2 of regolith, and 1000 g/cm2 for the levels at sea level on Earth. (The radiation dose on the lunar surface is not really known, so this is an estimate based on highly complex modelling.) That same estimate is mentioned in this video on civil engineering on the Moon:
I've been designing such habitats for a project to create a virtual lunar colony online. One area uses a configuration designed to allow in lots of natural light from above while still keeping the overall radiation low enough that a person can spend lots of time there. In that process I've been using the assumption that what they mean is that at least 700 g/cm2 in all directions yields this result. Today it occurred to me that it could instead mean that case over a hemisphere. At any rate, the only scenario where exactly the same amount of material stands between you and the outside environment is when you are standing dead center in an empty sphere with walls of uniform thickness, all of the same material (and you are also a dimensionless point, if one is especially a stickler about it).
Up to now I have been subtracting directions in which there is material of greater than 1000 g/cm2 from the total radiation dose, and I have been adding on higher radiation doses for the directions where there is less, as a proportion of all directions. It seems to be the best way to estimate dose within a given design. I also consider the proportion of time that a person might spend in an area with a given dose.
If these estimates aren't based on that simplification of a sphere, those results are off. If it is a model of a half-sphere, then I need to double the numbers. Or maybe it is modeled on something much more complex, like a point under a plane of that much material.
Does anyone know what assumption is used?