Why are neutrons in the nucleus stable vs their free counterparts?

In summary, a free neutron requires the same amount of energy to undergo Beta decay as it does to remain stable in a nucleus.
  • #1
iced199
29
1
If the free neutron decays in only 15 minutes, why are neutrons in the nucleus attached to protons stable? This has always bewildered me.


Just a side question, are 'tetraneutrons' stable or even possible?
 
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  • #2
Because if a neutron inside a nucleus decayed, it would leave a nucleus having one more proton and one less neutron. Whether this can actually happen depends on whether there is enough energy available, i.e. whether the mass of the first nucleus exceeds the mass of the second.
 
  • #3
Bill_K said:
Because if a neutron inside a nucleus decayed, it would leave a nucleus having one more proton and one less neutron. Whether this can actually happen depends on whether there is enough energy available, i.e. whether the mass of the first nucleus exceeds the mass of the second.

But still, surely a free neutron requires the same amount of energy to undergo Beta decay?
 
  • #4
In order for a decay process to happen there must be at least as much rest mass in the original nucleus as in the end products. Here's an example:

The 7Li nucleus has a mass of 7.016003 amu. If one of its neutrons beta-decayed, the result would be a 7Be nucleus, which has one less neutron and one more proton. But 7Be has a mass of 7.016926 amu, which is more. So there's not enough energy for this process to happen.
 
  • #5
In effect, a neutron in a nucleus gets the energy required for the decay, from the difference in binding energy between the initial and final nuclei.
 
  • #6
So is the extra mass from the energy of the newly created proton opposing the nucleus or am i completely missing this?
 
  • #7
The sum of the masses of the final nucleus and the electron has to be less than the mass of the original nucleus. Changing a neutron into a proton does increase the overall "internal electrical repulsion" of the nucleus, which would tend to increase the mass, but that's far from the whole story because of the strong nuclear force. Nuclear structure is a complicated subject. For a simplified model, look up the "semi-empirical binding energy formula." (Keep in mind that binding energy is negative.)
 
  • #8
jtbell said:
In effect, a neutron in a nucleus gets the energy required for the decay, from the difference in binding energy between the initial and final nuclei.

Thanks I understand now, didn't think about binding energies but a free neutron has a binding energy of it's 'system' - (which is just itself) of 0 so therefore any other state has a higher binding energy and so is preferred?
 

1. Why are neutrons stable in the nucleus?

Neutrons are stable in the nucleus because they are bound by the strong nuclear force, which is one of the four fundamental forces of nature. This force is responsible for holding the nucleus together despite the repulsive forces between protons.

2. How do neutrons maintain stability in the nucleus?

Neutrons maintain stability in the nucleus by balancing the attractive force of the strong nuclear force with the repulsive force of the electromagnetic force between protons. This balance allows the nucleus to remain stable and prevents it from breaking apart.

3. What makes neutrons stable compared to their free counterparts?

Neutrons are stable in the nucleus because they have a lower energy state than their free counterparts. When a neutron is free, it has a higher energy state and is more prone to decay. But in the nucleus, the strong nuclear force keeps the neutron in a lower energy state, making it stable.

4. Can neutrons become unstable in the nucleus?

Yes, neutrons can become unstable in the nucleus. This can happen when the nucleus becomes too large, leading to an imbalance between the attractive and repulsive forces. In these cases, the nucleus may undergo radioactive decay, releasing energy and particles in the process.

5. Why are neutrons and protons both considered stable in the nucleus?

Neutrons and protons are both considered stable in the nucleus because they are bound by the strong nuclear force, which is strong enough to overcome the repulsive forces between protons. However, as the nucleus becomes larger, the ratio of neutrons to protons may need to change in order to maintain stability.

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