[susus]

Why the electron is located out of the Nucleus ?

Is that because it's so little comparing to the proton , which make it, go fast and fast around the Nucleus because of it's size ?
Or there is another reason at all..

[Unknown008]

Well, the electron is not in the nucleus and that's a fact...

I don't think that there is a 'reason' behind this...

Antimatter for instance has its positron (positively charged subatomic particle) around its nucleus.

[DrBob1]

In all humility I think you might be better off asking this question on the Physics board. I'm a Chemist, I love electrons - use 'em all the time - but when you say "Nucleus" you jump out of my area of expertise. But that never kept me from giving an opinion!!
Historically, remember that it wasn't always a requirement that electrons be extranuclear. Before the Rutherford nuclear model of the atom, Thompson's Plum Pudding model reigned. In fact, even today we realize that electrons can exist both outside and inside the nucleus. Beta decay and electron capture are well known types of radioactivity, Both involve electrons INSIDE the nucleus. By themselves, neutrons are radioactive and decay to a proton and an electron, so you don't even need a whole nucleus to hold them. This is why the universe is filled with Hydrogen - with an 11 minute half life the neutrons from the Big Bang decayed years ago! Even the orbiting electrons show up in u nexpected places: I think Mossbauer Resonance Spectroscopy responds to s electron density in the nucleus.
So this question might be even deeper than you thought. Maybe a Nuclear Physicist can give you more information. Good Luck.