ok thank you all, at the end I've downloaded the Scatter plugin, I think it's the one more suitable for the thing i want to make. let's see if i'm able, thank you!

something like that:

i have searched for a tutorial or a plugin for a long time and i don't find anything. I would need to create a spheric and symmetrical bunch of identical particles... how people make explosions, carnations, fireworks...?? thank you very much.