Beta decay (s) & positrons

[vrus]

In Beta negative decay, a neutron changes into a proton and elctron and the electron is emmitted with a neutrino. Where does the neutrino come from ? Wouldn't that make the element a cation (+ve)?

 

In Beta positive decay, a proton converts into a neutron, releasing a positron and an anti-neutrino. Is the reverse possible ? As in will a high energy positron colliding (or by any other method) with a neutron form a proton again ?

[swansont]

The neutrino and positron, or antineutrino and electron, are created in the interaction that changes a down quark to an up quark, or vice-versa. This interaction is mediated by the W-boson, which is quite massive (~ 80.5 GeV) and thus has a very short range (i.e. have a small cross-section). The resultant nucleus will typically have an extra electron or deficit, depending on the interaction, but will eventually neutralize; that's at the atomic level and a relatively unimportant consideration in this context.

 

The reverse interaction is possible (antineutrino + proton -> neutron + positron) and is exploited in some types of neutrino detectors.

[[Tycho?]]

You've got your decays mixed up. Beta netative decay is N -> p + e- + antineutrino. Beta positive is p -> N + positron + neutrino

[swansont]

'']You've got your decays mixed up. Beta netative decay is N -> p + e- + antineutrino. Beta positive is p -> N + positron + neutrino

 

(I missed that). To vrus: The problem is that it is an antineutrino paired with the electron, so that lepton number is conserved.

 

 

 

Also: Since the emitted particles' spins are well-defined with their momenta and if the nuclear spin doesn't change in the decay, and since the decay is mediated by a vector Boson, the particles cannot be emitted back-to-back; in that alignment, they'd have to be emitted in the same direction. That sprang to mind because I was just visiting the lab where we did that experiment

[Tom Mattson]

In Beta negative decay' date=' a neutron changes into a proton and elctron and the electron is emmitted with a neutrino. Where does the neutrino come from ? Wouldn't that make the element a cation (+ve)?

[/quote']

 

Just a minor point: I don't think that you will find the product of that reaction referred to as a "cation" in any of the literature. That term is used in chemistry for an ion whose charge is made positive by removing electrons, not by converting neutrons into protons.

[DQW]

I suspect the OP believes the neutrino carries a charge.

 

Neutrinos (and antineutrinos) are chargeless.

[swansont]

I suspect the OP believes the neutrino carries a charge.

 

Neutrinos (and antineutrinos) are chargeless.

 

 

I thought the OP was just looking at the neutron/proton conversion. In reality' date=' the emitted electron or positron can strip away additional electrons. In the beta decay experiment I cited, there were Ar neutrals , Ar[sup']+[/sup], Ar²⁺ and Ar³⁺ even though you'd expect only Ar^- from a simple conservation of charge analysis.