why my previous intentions were doomed to fail – and what i’m planning to do about it. :-) ooops. i confused Cf-252 with Cf-254 – sorry about that! Cf-252 only undergoes SF to about 3%, while Cf-254 undergoes SF with almost 100% probability. the exempt quantity for Cf-254 is 1 kBq / 0.027 uCi.