Certainly charged particles from such a bomb would collect in the radiation belts, but I'd have to see how it would compare to the crap the Sun dumps into those belts every day.
I think what happens is this. The nuclear reaction produces gamma-rays which ionize and accelerate electrons in the vicinity of the upper atmosphere. The vaporized-ionized stuff that used to be the bomb makes a relatively small contribution. It's the Compton scattered electrons that ionize other molecules/atoms and this plasma cascade produces the ions and electrons that get trapped in the belts.
It's the initial rush of electrons away from the nuclear detonation that produces the EMP. The "numbers" on this would be hard to comeby without a decent space weather forcast of the upper atmosphere.
Space/Science » in reply to I'd like to see some numbers on that.
re: I'd like to see some numbers on that.