As a general rule, the faster it decays, the more dangerous it is. It is, of course much more complicated than that, though. Also, learn to spell "nuclear", please.
This calls for materials testing. Lets break out some of those low energy lightbulbs hooked to a variable frequency oscillator, an a LED, slip some Americanium from your smoke detector and put the material in the core between the bulb "neon" and test "empty" then "full" as to when the nuclear material triggers the LED to on. Go pick up some soil in your garden and see how much it gives off.