I was at an antique store where they had numerous pieces of Uranium glass glowing under a UV light last weekend.
I think it's funny that Uranium has this connotation of "glowing in the dark" which has nothing to do with the nuclear properties at all but rather very interesting optical phenomena that happen when you have an atom with a huge number of electrons like the way Thorium Oxide is good for gas lamps because it emits thermally in the visible range but not so much in the infrared.
That Pu238 pellet is surrounded by ash, I think they buried it in ash to hold the heat in and then uncovered it so you could see the glow. In this case it is driven by heat transport so the bigger of a mass you have the more the ratio of volume to area and the more it heats up.
That's very different scaling from this kind of thing
I think it's funny that Uranium has this connotation of "glowing in the dark" which has nothing to do with the nuclear properties at all but rather very interesting optical phenomena that happen when you have an atom with a huge number of electrons like the way Thorium Oxide is good for gas lamps because it emits thermally in the visible range but not so much in the infrared.