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Q & A: How can a nucleus be stable with many protons inside?

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Most recent answer: 03/27/2015
Like charges repel, unlike charges attract. considering, nucleus is positively charged consisting of protons which are positively charged and neutrons which have no charge. my question is, how the mass of a nucleus can be concentrated, knowing that like charges repel each other so shouldn't protons repel with each other and the nucleus itself?
- Faiza (age 16)

Hello Faiza,

The reason is that there are two kinds of forces involved inside the nucleus: electromagnetic and nuclear.  As you know, the electrical force is repulsive and long-ranged for like-signed charges. The nuclear force however is short ranged and attractive.   Protons are attracted to both other protons as well as neutrons.  So inside a nucleus there exists a battle between the electrical repulsion and nuclear attraction. 

The proton by itself is stable but the strong force is not quite strong enough to bind two protons. If you add a single neutron to the collection you get an (almost) stable tritium nucleus 3He.   4He is even more stable and lives forever.

There is an additional complication to the structure of nuclei, a much weaker force appropriately called the weak interaction.  This force allows the decay of a neutron into a proton + electron + anti-neutrino.  So if you get too many neutrons into a nucleus one of them may beta decay and leave a nucleus with one less neutron and one more proton.   It's this force that causes tritium to have a half-life of 12.3 years.


(published on 03/27/2015)

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