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Spining of protons and its effect on stability of nucleus

by shivakumar06
Tags: effect, nucleus, protons, spining, stability
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shivakumar06
#1
Jun13-14, 08:28 AM
P: 67
dear sir,
i heard that that proton spins about itselfand this helps in stability of nucleus. i also heard from the a friend that neutron has a proton and electron within it. this electron moves out from neuton making it proton and entering proton to form a neutron. sir i need to know if it is true and and many other interesting facts about nucleus and protons and neutrons. please guide me.
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ChrisVer
#2
Jun13-14, 01:53 PM
P: 916
1. The spin doesn't mean any spin about itself- it's just an intrinsic quantum number so it's better to avoid such visualizations of it (although it looks like angular momentum). The stability of the nuclei- I don't get how the proton spin affects that... In general the proton spin could allow or forbid some transitions of an excited nucleus state to another (because spin is coupled to electromagnetic forces). Of course the spin plays a role in the energy levels of a nuclei because it exists in the interactive hamiltonian.
For your second question, that is totally wrong...
The fact that the neutron's charge distribution is positive within a certain radius and negative outside doesn't mean that a neutron is a proton+electron..the only analogy I've seen of that, is that of pions rather than electrons and it's still an analogy and doesn't reflect any truth... Neither the fact that an electron can be captured by a proton to give a neutron means that thing for the neutron...
Drakkith
#3
Jun13-14, 02:36 PM
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Quote Quote by shivakumar06 View Post
dear sir,
i heard that that proton spins about itselfand this helps in stability of nucleus.
This is true in that the proton's quarks have the equivalent of orbital angular momentum, but I don't know how it affects the stability of the nucleus.

i also heard from the a friend that neutron has a proton and electron within it. this electron moves out from neuton making it proton and entering proton to form a neutron. sir i need to know if it is true and and many other interesting facts about nucleus and protons and neutrons. please guide me.
This is not true. Protons are composed of 2 up quarks and 1 down quark. The two up quarks have + 2/3 charge, while the down quark has -1/3 charge. Adding them up gives the proton a charge of +1. A neutron, on the other hand, is composed of 2 down quarks and 1 up quark. Adding the charges together we get a net charge of 0, making the neutron neutral overall.

Note that we can make neutrons in particle colliders without having to have protons and electrons. The fact that a proton and an electron can "combine" and form a neutron is simply the result of charge and mass conservation. The electron disappears and the energy and charge is used to convert one one of the up quarks to a down quark (a down quark is heavier than an up quark, so to convert an up quark into a down quark, energy and charge are required in order to satisfy conservation laws).

kurros
#4
Jun14-14, 08:37 PM
P: 366
Spining of protons and its effect on stability of nucleus

Quote Quote by Drakkith View Post
This is true in that the proton's quarks have the equivalent of orbital angular momentum, but I don't know how it affects the stability of the nucleus.
It is an entirely separate matter. If you take a proton, and change the quark spin or orbital angular momentum, then we don't call that thing a proton anymore, we call it a different particle (e.g. Δ+). This is because changing the internal angular momentum changes the internal energy by a lot, i.e. changes the mass. Anyway they are very unstable so no long-lived nuclei will contain such a particle.
Drakkith
#5
Jun14-14, 08:50 PM
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Quote Quote by kurros View Post
It is an entirely separate matter. If you take a proton, and change the quark spin or orbital angular momentum, then we don't call that thing a proton anymore, we call it a different particle (e.g. Δ+). This is because changing the internal angular momentum changes the internal energy by a lot, i.e. changes the mass. Anyway they are very unstable so no long-lived nuclei will contain such a particle.
Hmmm... I was reading on the proton spin crisis and how a significant portion of the angular momentum comes from something other than the quark's spin. Is that correct?
kurros
#6
Jun14-14, 09:01 PM
P: 366
Quote Quote by Drakkith View Post
Hmmm... I was reading on the proton spin crisis and how a significant portion of the angular momentum comes from something other than the quark's spin. Is that correct?
Well, I am not super familiar with that issue, but certainly the proton is not just a bag of 3 quarks. It is a soup of strongly-interacting junk. There are lots of "sea" quarks and gluons in there, as well as the three "valence" quarks. So the spin and angular momentum from all that junk contributes as well.
ChrisVer
#7
Jun15-14, 08:07 AM
P: 916
I think the calculations for the gluon and sea quarks contribution in the proton spin are already calculated and give zero result... that's why the spin-problem arises and people look into COMPASS.
Bill_K
#8
Jun15-14, 08:17 AM
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Quote Quote by ChrisVer View Post
I think the calculations for the gluon and sea quarks contribution in the proton spin are already calculated and give zero result... that's why the spin-problem arises and people look into COMPASS.
It's orbital. From this article:

It was recently shown ... that the modern spin discrepancy can be rather well explained in terms of standard features of the non-perturbative structure of the nucleon, namely relativistic motion of the valence quarks, the pion cloud required by chiral symmetry and an exchange current contribution associated with the one-gluon-exchange hyperfine interaction.
... ...
The very clear physical picture ... is that the spin of the proton resides predominantly as orbital angular momentum of the u (and u) quarks. In contrast, the d (and d) quarks carry essentially no orbital angular momentum.
HeavyMetal
#9
Jun15-14, 01:04 PM
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Quote Quote by shivakumar06 View Post
i also heard from the a friend that neutron has a proton and electron within it. this electron moves out from neuton making it proton and entering proton to form a neutron.
Your friend may have been talking about beta decay and electron capture. Beta decay is the simultaneous emission of an electron and an electron antineutrino, converting a neutron into a proton ([itex]n^{0} \longrightarrow p^{+}+e^{-}+\overline{\nu}_{e}[/itex]). Electron capture is the collision between an electron and a proton making a neutron and an electron neutrino ([itex]e^{-}+p^{+} \longrightarrow n^{0}+\nu_{e}[/itex]).
Bill_K
#10
Jun15-14, 01:26 PM
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Quote Quote by shivakumar06 View Post
i heard that ... i also heard from the a friend that ...
shivakumar06, it helps the discussion greatly if you have a specific reference to cite, either a book or something accessible on the web.

"I heard that", and "a friend told me" could mean almost anything!
mfb
#11
Jun16-14, 04:07 PM
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Quote Quote by shivakumar06 View Post
i heard that that proton spins about itselfand this helps in stability of nucleus.
There are many types of spin involved, the statement is too unclear for a specific answer.

One aspect not mentioned before: due to spin, protons (and neutrons) are fermions and not bosons. Bosons would form nuclei that would look completely different.

i also heard from the a friend that neutron has a proton and electron within it.
This is wrong.

and many other interesting facts about nucleus and protons and neutrons. please guide me.
-> books about nuclear and particle physics
shivakumar06
#12
Jun17-14, 02:31 AM
P: 67
dear sir
i would like to thank you for you guidance and i request you to tell me about books and website on nuclear and particle physics.


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