Let me start with your statement, that " If it is made of proton, electron and neutrino it could be as stable as atom of hydrogen? "
The answer to this is that not really. A neutron is not made of a proton, electron and an antineutrino. These particles are only its decay products. A neutron is made of 3 quarks, one up quark, and 2 down quarks and many many "intermediate particles" called gluons which carry the interaction between the quarks. These gluons are exchanged very often, so the quarks feel each of other.
Neutrons do not always decay. Let me be more specific. You know, that most of the matter around us is made out of atoms. Atoms have nucleae and electrons. In the nucleus you usually find protons and neutrons. I am sure you agree with me, that in your everyday life, you DO NOT SEE cars or houses or ... decaying, because their neutrons would decay! In other words, when a neutron is hidden in an atomic nucleus, it is extremely stable and it does not decay according what you wrote. ( Yes, there are some radioactive elements which are not stable, and their neutrons decay into protons, but let us leave them aside for a second.)
On the other hand, if you have a free neutron, taken away from a nucleus, it does decay. So why is that? First of all, you know that so far science recognizes 4 types of interactions (forces), namely the electromagnetic, gravitational, weak and strong interaction. When a neutron is buried into a nucleus, it feels mostly the strong interaction. The quarks are "tight" very strongly to each of other, and it is not allowed for them to change into uud ( the proton) and electron and antineutrino. For the neutron decay, the weak interaction is responsible. If a neutron is freed from a nucleus, the weak interaction of quarks will play the major role, and since the proton is lighter than a neutron, it is allowed for the neutron to go to this lighter stage by radiating out an electron and antineutrino. If you are still wondering and still have some questions, please ask
- bye, Arnold Pompos
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