How does the neutron turn into a proton and electron in Beta Decay?

[Lightmeow]

I learned that in chemistry that when a unstable element is going through Beta decay, a neutron splits into a proton and electron, the electron being the Beta particle. As far as I know, the protons and neutrons are made up of quarks, which are elementary particles. The electron is also a elementary particle. But how do both quarks and electrons make up an atom? I did some research, and was unable to find a good explanation for this. Could some one please explain?

 

Thanks in advance.

[ajb]

As far as I know, the protons and neutrons are made up of quarks, which are elementary particles.

Yes, this is true.

 

The tree level diagram for beta decay can be found at http://en.wikipedia.org/wiki/Beta_decay#/media/File:Beta_Negative_Decay.svg

 

Basically we have a d 'emitting' a W^{-} to become a u together with an electron and an antineutrino.

[swansont]

Quarks (the up and down "flavors") make up the neutrons (udd) and protons (uud) of the nucleus. The electron that's emitted is created, rather than being contained in the nucleus (which is also true of the antineutrino that is emitted). The condition that has to hold is that the system can lower its energy by doing the conversion.

[Lightmeow]

OK, that makes sense. Another thing the teacher said, that when you get the mass of a proton, and the mass of an electron, the mass of a neutron is the mass of the proton and the electron added up(That was she said proved a neutron is an electron + proton). I'm assuming the difference in weight is that the down quarks weigh a little more?

[ajb]

OK, that makes sense. Another thing the teacher said, that when you get the mass of a proton, and the mass of an electron, the mass of a neutron is the mass of the proton and the electron added up(That was she said proved a neutron is an electron + proton). I'm assuming the difference in weight is that the down quarks weigh a little more?

Her proof is nonsense.

 

You cannot think of a neutron as a bound state of an electron and a proton or something like that. It is wrong to think of the electron as being inside the neutron or anything like that.

[robinpike]

Yes, this is true.

 

The tree level diagram for beta decay can be found at http://en.wikipedia.org/wiki/Beta_decay#/media/File:Beta_Negative_Decay.svg

 

Basically we have a d 'emitting' a W^{-} to become a u together with an electron and an antineutrino.

 

 

Quarks (the up and down "flavors") make up the neutrons (udd) and protons (uud) of the nucleus. The electron that's emitted is created, rather than being contained in the nucleus (which is also true of the antineutrino that is emitted). The condition that has to hold is that the system can lower its energy by doing the conversion.

 

Isn't it a little odd that the elementary down quark can shed a -1 of electric charge if the quark is indeed elementary? Does this suggest that electric charge is separate to an elementary particle? If not, how can the change of down quark (-1/3) --> up quark (+2/3) and W (-1), simply start with that step?

[ajb]

Isn't it a little odd that the elementary down quark can shed a -1 of electric charge if the quark is indeed elementary?

Loosely in changing its charge the quark changes flavour; it becomes another type of quark. The weak force is responsible for allowing such changes. Each quark is still, as far as we know fundamental.

[swansont]

Isn't it a little odd that the elementary down quark can shed a -1 of electric charge if the quark is indeed elementary?

Since that doesn't actually happen, no, it's not odd.

[Enthalpy]

One argument against a neutron composed of a proton plus an electron (...that idea was fashionable looooooong ago) is the beta plus radioactivity, where the proton decomposes in a neutron plus a positron (positive electron, or antielectron) and a neutrino.

 

It happens with nuclei that have too many protons and too few neutrons. In that case, the mass difference between the older and newer nuclei favours the transformation in this direction. Which implies that all protons and neutrons in the nuclei have an influence, it's not a matter of one neutron or one proton alone that decomposes. Well, this was already clear from the neutron's stability in many nuclei, while a lone neutron decomposes.

[robinpike]

Yes, this is true.

 

The tree level diagram for beta decay can be found at http://en.wikipedia.org/wiki/Beta_decay#/media/File:Beta_Negative_Decay.svg

 

Basically we have a d 'emitting' a W^{-} to become a u together with an electron and an antineutrino.

 

In the conversion process, is the W- particle a real particle? Wikipedia has the mass of the W- boson as being much greater than that of a proton or a neutron.

[swansont]

 

In the conversion process, is the W- particle a real particle? Wikipedia has the mass of the W- boson as being much greater than that of a proton or a neutron.

 

It's a virtual particle. The W doesn't exist very long, which is why this is a short-ranged interaction, small cross-section, and doesn't happen as regularly (all other things being equal). That's why it's "weak"

[ajb]

In the conversion process, is the W- particle a real particle? Wikipedia has the mass of the W- boson as being much greater than that of a proton or a neutron.

It is virtual and so not constrained to obey the mass-shell condition.

[Enthalpy]

 

In the conversion process, is the W- particle a real particle? Wikipedia has the mass of the W- boson as being much greater than that of a proton or a neutron.

 

Even if it were permanent, a different possibility would have been the interaction energy, which lets particles weigh together less than if separated. This tends to be more important at smaller scale.