Radioluminescent Generator (RLG)

I know, this concept has been around for a while and examples may or may not have been built, depending on who you ask. For those that don't know, a Radioluminescent Generator is similar to a Radioisotope Thermal Generator (electricity from radiation) except that a beta radiation source illuminates a phosphor, which powers solar panels, which powers your electronics. They are also called "betavoltaic batteries", and "optoelectric nuclear batteries" according to wikipedia.

Aaanyway, I want to build one. Here is my idea: six 2x2" solar panels, arranged in a box with the photovoltaic sides facing inwards. Inside the box, a jar of sodium aluminate (the phosphor), mixed with a clear epoxy to that the powder is evenly exposed to the source. In the middle of the "core", a chunk of uranium ore from www.unitednuclear.com. The ore emits beta rays, which charge the sodium aluminate. If I'm lucky the phosphor then glows bright green. If I'm even luckier this bright green glow registers a minute voltage on the solar panels when it is placed in the box. Some circuitry from Radio Shack will allow the box to power something small like a digital wristwatch for ~15 years, until the phosphor degrades and stops glowing.