Electron K-capture question

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In summary, during K-capture, an electron is essentially transformed into a neutrino by emitting a W- boson and then being absorbed by a u quark, resulting in the proton being changed into a neutron. This process demonstrates that elementary particles can interact and change forms while still preserving various symmetries such as electric charge, color charge, spin, lepton number, and baryon number. CP symmetry may be violated in some interactions, but CPT symmetry is always preserved. Spin is not related to linear momentum, but there is a quantity called helicity which is the projection of spin in the direction of motion.
  • #1
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If I understand correctly, when a proton captures an electron through K-capture, the proton is changed to a neutron and an electron neutrino is created in the process.

The electron is an elementary particle, and yet the newly created neutron is composed of quarks, which are elementary also. What happened to the electron? It seems as though the electron does not behave as an ‘elementary’ particle in this process. What am I missing?
 
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  • #2
One way to look at this process is that the electron emits a W- boson. This particle carries away the electron's negative charge and so emitting this particle essentially changes the electron into a neutrino. The W- boson is then absorbed by a u quark, which changes the u quark into a d quark. Since the proton is uud and the neutron is udd, this changes the proton into a neutron. Try googling electron capture and looking at the Feynman diagrams.
 
  • #3
I see. So my new understanding is that the elementary particles (of the standard model) can interact and change forms. The interactions/transformations must preserve symmetry (CP or CPT).

Correct?
 
  • #4
There are multiple things which must be conserved in the interactions, including electric charge, color charge, spin, lepton number, and baryon number. There are some interactions that violate CP symmetry, but it appears that CPT symmetry is always preserved.
 
  • #5
Thanks phyzguy.

Regarding spin, is it related to momentum? I don't mean the angular momentum of the particle, I mean the directional momentum. Is the spin orientation independent of the particle's velocity and/or momentum direction, or is there a strict relationship?
 
  • #6
No, spin has nothing to do with linear momentum. It is not dissimilar to taking a spinning top and throwing it (in space); the top can spin any which way just fine. Of course this is quantum mechanics so when you measure the spin relative to some axis it will be quantised. There is however an important quantity called helicity which is the projection of spin in the direction of motion, which perhaps is what you are thinking of.
 

1. What is Electron K-capture?

Electron K-capture is a type of radioactive decay process in which an electron from the innermost shell of an atom is captured by the nucleus, resulting in the emission of a neutrino and a gamma ray.

2. How does Electron K-capture occur?

Electron K-capture occurs when an atom's nucleus has a deficiency of neutrons, making it unstable. The nucleus then captures an electron from the innermost shell, converting a proton into a neutron and reducing the overall charge of the nucleus.

3. What is the significance of Electron K-capture?

Electron K-capture is important in nuclear physics and chemistry because it plays a role in the stability of atoms and their isotopes. It also helps in understanding the structure of the nucleus and the forces that hold it together.

4. What is the difference between Electron K-capture and Electron capture?

Electron K-capture is a specific type of electron capture, where the captured electron comes from the innermost K-shell of an atom. In general, electron capture refers to any process in which an electron is added to an atom or ion, resulting in a change in the atomic number.

5. How is Electron K-capture used in practical applications?

Electron K-capture is used in nuclear medicine, in which radioactive isotopes that undergo electron capture are used for medical imaging and cancer treatment. It is also used in research to study the properties of nuclei and to understand the formation of elements in the universe.

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