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Possible Duplicate:
How come neutrons in a nucleus don't decay?

It is known that free neutron decays in 15 minutes on average. Why is it much more stable when "placed" in nuclei?

Edit: I see that this question had been asked already (here) and can be closed.

Community
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Murod Abdukhakimov
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Neutron decay produces a proton. Free neutron decays since this leads to a lower energy state. However, if this happens in a nucleus then due to the already existing positive charge of all the other protons, it will result in a higher energy state. In fact, the opposite may happen if a nucleus has an excess of protons: some of them may transform into neutrons. See beta decay for more on both transformations. On average the heavier the nucleus the higher the stable ratio of neutrons to protons.

Adam Zalcman
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