Perfect clarity is difficult, but the IAEA (which designed that graphic) did their homework. The symbol was tested with 1,650 people from a wide variety of countries. I haven't been able to find details on their results, but I can't imagine they would have settled on this design if there were straightforward improvements to be made.
(With regard to your particular ideas, any graphical division between sections in the graphic could be misunderstood as a protective barrier against the danger represented by the skull. Wrong message entirely!)
And it's certain to be an improvement on the standard radioactivity symbol. In a global context, recognition of that symbol is poor -- it's frequently understood as a propeller or a flower.
(With regard to your particular ideas, any graphical division between sections in the graphic could be misunderstood as a protective barrier against the danger represented by the skull. Wrong message entirely!)
And it's certain to be an improvement on the standard radioactivity symbol. In a global context, recognition of that symbol is poor -- it's frequently understood as a propeller or a flower.