Understanding Beta Decay: The Role of Quarks, Leptons, and Bosons

In summary, the conversation discusses the process of beta minus decay and the role of the W boson in converting a down quark into an up quark. It also addresses the creation of virtual particles and the conservation of charge and lepton number. The conversation concludes by addressing the possibility of a proton-electron pair and clarifying the missing factor in the neutron decay process.
  • #1
Comeback City
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These questions came to mind after my physics teacher told us that a neutron is actually a "proton-electron" pair. He then said in beta minus decay, when the neutron decays, the electron is released and only the proton remains. I'm pretty sure this is incorrect, though, but can any confirm it?
I get that the proton is made up of 2 up quarks and 1 down quark, and the neutron is 1 up quark and 2 down quarks. Can anyone confirm or deny if my following understanding of this process is correct?...
In beta minus decay, a down quark in a neutron decays into an up quark. This releases a W- Boson, which then decays into an electron and an electron anti-neutrino upon exiting the nucleus.
Now, the questions...
1) How does the down quark decay into an up quark? I've read several different explanations for this, including that virtual electron-positron pairs pop into and out of existence in the nucleus, and the positron can give the +1 charge to the down quark needed to change it into an up quark (explains conservation of charge).
2) Lepton number has to be conserved, which is why the electron and the electron anti-neutrino are created. Does the W- Boson have exactly the mass of the electron + neutrino?
 
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  • #2
Hi,

1) you only need the W boson to turn one quark into the other. W bosons are electrically charged, and while turning a down quark into a up type quark, they leave with both the charge and the "downness"-"upness" difference (even if it's a very unclear way to put it - but these characteristics are the analog of an electric charge. The electric charge is the charge of the electromagnetic interaction, whereas the "type" would be the charge of the weak interactions - not to be confused with the flavour, which is just a repetition of the same charges: up, charm and top quarks have the same charges, which differ from those of the associated down, strange and bottom quarks). When they become an electron-neutrino pair, they release exactly these charge and "type" differences.

2) the W boson involved would be virtual, so it doesn't have to have its own mass. If it was real, its mass would feed the electron-neutrino masses, but also their kinetic energies. The eventual masses just have to add up to something smaller than the initial mass.

If you want to understand this at a deeper level, you should google "standard model of particle physics", "yang-mills theories", ... but it requires quite a background.
 
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  • #3
Thanks for the response!
Another question though:
Is the "virtual w boson" created as a result of the decay, or is it residing elsewhere before the decay happens?
 
  • #4
Comeback City said:
Is the "virtual w boson" created as a result of the decay, or is it residing elsewhere before the decay happens?

It's "created" by the decay. This should be taken carefully since virtual particles are a way of representing an interaction within a perturbation approach in QFT, and are not to be thought of as temporary propagating particles.
 
  • #5
Comeback City said:
a neutron is actually a "proton-electron" pair.

This is not correct. Since the proton and electron both have spin-1/2, this would imply a neutron has either spin-0 or spin-1. But it also has spin-1/2.
 
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  • #6
Q.B. said:
you only need the W boson to turn one quark into the other.
Q.B. said:
It's "created" by the decay.
How does the W boson cause the quark decay and also get created by the quark decay?
 
  • #7
Vanadium 50 said:
This is not correct. Since the proton and electron both have spin-1/2, this would imply a neutron has either spin-0 or spin-1. But it also has spin-1/2.
Is it even possible at all to have a proton-electron pair?
 
  • #8
Comeback City said:
Is it even possible at all to have a proton-electron pair?
Yes, a hydrogen atom. Your neutron decay description is missing one important factor. The decay also produces a neutrino and that is how the angular momentum is balanced: ##n\rightarrow p + e + \nu##.
 
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  • #9
mikeyork said:
Yes, a hydrogen atom.
I just overlooked the obvious.:eek: I was thinking of it in a different context where the electron would be bound with the quarks of the proton (which, now thinking about it, most likely cannot work anyways)
mikeyork said:
Your neutron decay description is missing one important factor. The decay also produces a neutrino and that is how the angular momentum is balanced: n→p+e+νn→p+e+νn\rightarrow p + e + \nu.
I mentioned that in the original post...
Comeback City said:
This releases a W- Boson, which then decays into an electron and an electron anti-neutrino upon exiting the nucleus.
 

1. What is beta decay?

Beta decay is a type of nuclear decay that occurs when an unstable atom releases energy in the form of a beta particle (either an electron or a positron) in order to reach a more stable state.

2. How does beta decay differ from alpha and gamma decay?

Beta decay differs from alpha and gamma decay in terms of the particles emitted and the amount of energy released. While alpha decay releases an alpha particle (two protons and two neutrons) and gamma decay releases a high-energy photon, beta decay releases an electron or positron.

3. What is the role of the weak nuclear force in beta decay?

The weak nuclear force is responsible for beta decay as it is the force that governs interactions between subatomic particles. During beta decay, the weak nuclear force is responsible for the transformation of a neutron into a proton (or vice versa) and the release of a beta particle.

4. Can beta decay be controlled or harnessed for practical use?

Beta decay can be controlled and harnessed for practical use in a process called beta decay energy conversion. This involves capturing the energy released during beta decay and converting it into electricity, similar to how nuclear power plants harness the energy from nuclear fission.

5. Are there different types of beta decay?

There are three types of beta decay: beta minus decay, beta plus decay, and electron capture. In beta minus decay, a neutron in the nucleus converts into a proton and releases an electron and an antineutrino. In beta plus decay, a proton in the nucleus converts into a neutron and releases a positron and a neutrino. Electron capture involves an electron from the inner shell of an atom being captured by the nucleus, resulting in the emission of a neutrino.

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