Golden Shields

The assumption seems to be that a radiation shield made of water or
dirt would be very thick (on the order of two metres), while one of
gold or lead would be very thin (on the order of ten centimetres or
so). I can kind of see how a thin shield, even if made of dense
stuff, could generate dangerous secondaries whick don't have to travel
very far and thus make it into the habitat.

But what if your golden shield were a metre or two thick? I'm
guessing that the secondaries problem wouldn't be a problem in that case.

Having said that, I don't really know, and am prepared to be wrong on
this.