A Free neutron will dekay in about 14 minutes into proton, election and other particles. But neutron is stable when it is with proton. Why is this? Also, how can this be explained in wave theory?
Yes, into a proton, electron and anti neutrino due to weak force.
As far as I know, just a fact. Do not know an explanation.
Another question is why the proton is stable, believe some say it really is not, but life time extremly long.
Because there exist particles, into which it can transform, under the weak interactions, namely the proton, the electron and the electron antineutrino.
The neutron isn't stable when ``it's with the proton''. Only the strong interactions are stronger than the weak interaction (except in nuclei that do transform into others, by emitting electrons and electron antineutrinos).
It's the properties of the weak and strong interactions that imply that a particle like the neutron can transform into certain others and a particle like the proton can't.
And these properties imply statements for all the known particles-they weren't made up only for the proton and the neutron; and these statements turn out to be correct.
For stable nuclei, the Pauli exclusion principle forbids the decay of a neutron into a proton, the proton needs an available quantum state at lower energy. All states al filled with protons with spin up and down.
Inside an unstable nuclei, the decay of a neutron is possible by beta decay. The resulting proton can fill an available energy state.
The decay of a neutron is well explained by previous comments, by weak interaction we can change the flavour of one of the neutron's quarks by emission of a W boson.
A free neutron is unstable, decaying to a proton, electron and antineutrino with a mean lifetime of just under 15 minutes (881.5±1.5 s). This radioactive decay, known as beta decay, is possible because the mass of the neutron is slightly greater than the proton. The free proton is stable.
wikipedia
Without an electric charge, the neutron is unable to reflect or receive coherent feedback. Thus it's existence in a state of narcissistic paranoia continues into increasing entropy until it is no longer relevant.
( Sorry -- I couldn't resist.)
To complement the answer of Mushtaq Ahmad :
the neutron can decay into a proton, an electron and an antineutrino because its mass is higher than the sum of the masses of the three products, so the decay can produce an excess energy which is a condition for a spontaneous reaction (any reaction absorbing energy needs that this energy is brought by some external process and is thus not spontaneous).
The decay is possible because there is an internal mechanism, which is the decay of a d-quark into an u-quark by the weak interaction.
The neutron is unstable in a nucleus when the mass of this nucleus is higher than the sum of the masses of the daughter nucleus + electron + antineutrino. It is stabilised in the opposite case. In this energy balance, the very small mass of the antineutrino is often neglected.
The Pauli principle can play a role in the probability of the decay (thus the half-life) but never forbids the decay when it is energetically possible.
Hi Mr.François Tondeur.
First of all, you are not taking into account, for the unstable nucleus case, the binding energy of the nucleons which is absolutely necessary. On the other hand, I do not agree with you with the statement that the sum of energy plays the essential role in the decay process because you are describing an unstable nucleus with a definition which is always satisfied. I think the sum of masses is a consequence of deeper conservation laws which actually model the process.
Best regards. Jose A.
Of course, the binding energy of the nucleons is included in the mass of the nucleus, this is one of the first lessons in introductory nuclear physics:
nuclear mass = sum of nucleon masses + binding energy/c2.
This is why the tables of experimental atomic masses generally include a column with the nuclear binding energy. And the so-called nuclear "mass" formulas are indeed theories of the nuclear binding energy.
As soon as a decay mechanism exists, the possibility or impossibility of a decay is ruled by the conservation of mass-energy. When the decay is energetically possible, its probability is indeed ruled by other conservation laws. In the case of nuclear beta- decay, the probability is much higher when the Pauli exclusion allows the newly created proton to occupy the same single-particle state as the initial neutron (superallowed transition). But this is not the case in most of the nuclear beta- decays, that concern nuclei wit N>Z, for which the analog state, in which the p take the same s-p state as the initial neutron, is higher in energy than the ground state of the daughter nucleus, and may not be energetically accessible in the decay.
@François Tondeur. Thank you for your answer. You are right, on the previous comment I felt the need of a better explaination to the problem because some sentences were poorly argued. But now the question is accurately answered.
Best regards. Jose A.
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