The GRPH Element is Graphite, an element that is used in nuclear reactors to slow down neutrons so that a better reaction can take place. It will slow neutrons down considerably from 3 pixels (Like half of it's speed). It will look very black.

I'm suggesting this, mainly because I've been attempting to make a reactor in the game and I have been researching how well polonium (a neutron source) would react with plutonium. I checked with half of the screen split to have one side with no moderator and one with the moderator (I used water). The one with the moderator worked better, but it stopped working when the water converted into steam. It'd be very useful for a lot of people to have a moderator element like graphite.