Normally what is required and used to make a relatively thin shield to block harmful gamma rays is to make it out of an element, such as lead, with large atomic nuclei which absorbs the gamma rays.
But is it at least in theory possible to make a relatively thin shield, say, just 1cm think, to block 99% gamma rays but make it only out of lighter and cheaper chemical elements such as carbon silicon iron etc by making the material have a molecular or crystalline structure that is such that it creates molecular electron orbitals that can readily absorb gamma rays thus remove the need for using heavy atomic nuclei to absorb most of the gamma rays?
I tried my best googling this but got nowhere.

@humy

The Point is that X-ray for all practical purposes don't interact with the electrons, buut with the nuclei (that is the Basis of X-ray diffraction and related Methods).

And you can't pack metals better than in a dense packing. So there would be some effect required to pack the Atoms "more effiecient" for x-ray Absorption.