# What makes a nucleus unstable?

My question is simply that - what makes a nucleus unstable? What exactly causes a nucleus to start breaking apart in the first place? Is it the Coulomb force between the neighboring protons?

I'm just curious.

• Breaking apart in radioactive decay? – HDE 226868 Nov 29 '14 at 1:57
• By the way, I believe the strong nuclear force between the protons would definitely overwhelm any electromagnetic forces between them. Lubos Motl explains it pretty well here. – HDE 226868 Nov 29 '14 at 2:10
• Possible duplicates: physics.stackexchange.com/q/9661/2451 and links therein. – Qmechanic Jul 19 '16 at 17:44

Even if the the strong nuclear force is the most powerful force over subatomic distances. The electrostatic force is almost always significant, and, in the case of beta decay (which also involves a transformation of a proton into a neutron), the weak nuclear force is also involved. But the basic answer is yes, you cannot two protons together (Helium 2 doesnt exist, at least in a stable form), you need neutrons to compensate and add more strong force to avoid the electrostatic repulsion. Even if the strong force is stronger, it acts over very short distances, that is why elctrostatic repulsion wins sometimes, specially on large nuclei whare the strong force of a proton on the core has little influence on a proton on the external shell, but the lectrostatic force, is still strong as it decays slowly with distance remember that the range of the strong force is limited to distances on the order of a few $10^{-15}$ meters)