I foudn a box of photomultiplier tubes and I opened up one of the tube boxes and it is a Harshaw scintillation detector tube. However at the top was an aluminum "pot" about 1.75" wide with a piece of glass over the top. The inside has some sort of weighty matter that is almost exactly this color green:
http://time2rally.com/troy%202.jpg

I know it is a radioactive source of some type because the manufacturer is Isotopes, inc, bearing type code S64. I thought the type may refer to the periodic symbol and isotope, but S is for sulphur and it doesn't have a 64-nucleide isotope, plus the isotopes have short halflives.

I found some datasheets that were for another tube that said the radioactive source was Iron-55. However, what little I can find on it says that the color isn't different than normal iron. I know that uranium is used for a green pigment, but it isn't THAT heavy. I also don't have a black light to see if it glows like uranium does. (that, and it's cloudy outside)

Keep in mind that this thing is over 40 years old, so if its got a short half-life, I'm keeping it.

pics or it didnt happen

Sounds interesting, but I'm not sure how much anyone can help you, especially since it seems you have done a lot of research.

Are you sure it's radioactive? Not all isotopes are radioactive, hence the term "radioactive isotopes"...

this man has a point, many isotopes arent radioactive...

and not all isotopes have very short half lives... carbon-14 has a half life of more than 5000 years... hell some of the radioactive isotopes...most uranium isotopes have half lives longer than we will be around for...

I can assure you that if it was taped to a photomultiplier tube that was designed to detect nuclear decay, it has some sort of decay. I can tell you that it is negligibly radioactive in the gamma spectrum as I tested it with some ridiculously expensive lab equipment.

I believe the datasheets for the tubes let on that they can be used as neutron detectors as well. So either its going to be an alpha, beta, or neutron source. Looking up common neutron emitters leads me to believe it may be a radium-beryllium source.

Alphas...