EMP from Nuc. Reaction

[Razzor7]

I need to know if nuclear material equal in volume to two marbles could be reacted in a way to cause an EMP that would disrupt an average complexity computer system (e.g. laptop). My suspicious is that this wouldn't reach critical mass, wouldn't create a chain reaction, and .'. no EMP. But I have no idea what aspect of nuclear reactions cause EMPs. Even if this is an ambiguous area of theory, I get the feeling that my question has been clearly answered experimentally.

Thanks!

[Astronuc]

A pure fissile material the size of two marbles (let's day 1 cm diameter each) would not go critical.

Radiation is a more likely problem from a nuclear explosion, but the intensity would depend on distance.

Similarly EMP impact would depend on the size of the nuclear explosion and distance from it.