Hopefully, you ain't trying anything with uranium-238 or thorium.
I really don't know if this could be possible, but you could try americium that you can find from smoke detectors. I believe over some 70 years or so, it turns useless for your purpose as it decays into neptunium. Moral? Buy new smoke alarms! (Well, I don't think there were smoke alarms back in 1940. If there were, they're going to be rare out now)
As for the "americium reactor" (no naming credits accepted), you can try bombarding the electrons onto the americium using a cathode ray tube (silly idea, I must say. But you never know, it just might work).
Let's see if anyone can rectify this post (if wrong, of course) and discuss the "reactor".