# [Beta decay] Nuclear physics

What is difference between beta particle and electron? I mean in spin, mass or other properties.

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Simon Bridge
Homework Helper
Nothing.

Thanks

Simon Bridge
Homework Helper
No worries - conceptually a beta particle comes from a nuclear disintegration, so it is a handy shorthand.
Saying I detected a beta particle from some atom is a bit different from saying I detected an electron from that atom.

Given a free electron, there is no way of telling if it came from a nucleus or an electron shell or pair production even.
You need some other information - like the presence of a beta-unstable radio-isotope, and shielding.

Historically, beta rays were named before they were identified with cathode rays and so with electrons.
Technically beta particles may be positive or negative - but we would usually specify "beta-plus" if the positron is intended.

It's all good fun.

Thanks alot

Thanks I m confused when I studied that in beta decay W- decay into electron and antineutrino. when we see the spin of w- then it is -1.this is TRUE only when electron and antineutrino both have spin half (down).sir this is my own thinking may be I m wrong.thanks

Nugatory
Mentor
Thanks I m confused when I studied that in beta decay W- decay into electron and antineutrino. when we see the spin of w- then it is -1.this is TRUE only when electron and antineutrino both have spin half (down).sir this is my own thinking may be I m wrong.thanks
Beta decay is a process by which a beta particle - which is an electron - is produced along with an antineutrino as a proton converts into a neutron. Yes, this terminology is somewhat confusing.... It came about for historical reasons, because the radiation was observed and given its name before the particles involved were identified and the process understood.

Thanks

Simon Bridge
Homework Helper
Beta decay is a process by which a beta particle - which is an electron - is produced along with an antineutrino as a proton converts into a neutron.
##p^+ \to n^0 + e^- + \bar \nu_e## does not conserve charge?

You mean: ##n^0 \to p^+ + e^- + \bar \nu_e##

Thanks I m confused when I studied that in beta decay W- decay into electron and antineutrino. when we see the spin of w- then it is -1.this is TRUE only when electron and antineutrino both have spin half (down).
To conserve angular momentum, the electron and neutrino spins need to be aligned - you are thinking.

The usual sin-up/spin-down terminaology only applies in an external magnetic field like that of the nucleus of an atom on in a Stern Gerlach apparatus. There is no "up" or "down" in space.

Odd things can happen in the virtal particle transition though - consider, is total energy conserved as the W -> e+nu. ?

Sir you mean that here we cannot consider spin?sir what do you think energy is conserved here.since we know that W is havier .and if we try to re combine electron and antineutrino then what happen?

Nugatory
Mentor
##p^+ \to n^0 + e^- + \bar \nu_e## does not conserve charge?

You mean: ##n^0 \to p^+ + e^- + \bar \nu_e##
D'oh... Yes, of course.

jtbell
Mentor
sir what do you think energy is conserved here.since we know that W is havier .
The W in this case is "virtual". Energy and momentum are conserved, but the mass of a virtual particle is generally not the same as the mass of a "real" particle. Particle physicists often use the jargon "off the mass shell" for virtual particles, where "on the mass shell" means "having the mass that you see in the standard tables."

Thanks jtbell

Simon Bridge
Homework Helper
I think smk wants a definitive answer to the conservation of angular momentum issue ;)
If electron and neutrino spins must be aligned, then that suggests the proton must have the opposite of the spin of the initial neutron.

Thanks

And another question arise here that as we know that in nuclei protons and neutrons occupy definite levels in nucleonic shells.now question is that when neutron transformed into proton then where the proton goes? I mean it will stay in the same level as that of neutron or jump into another level? Thanks

ChrisVer
Gold Member
In strict language, yes there would be a small jump(due to coulomb potential). The nucleus itself can change.. but in general and simple models this doesn't happen, because the strong force doesn't distinguish between neutrons and protons (isospin symmetry).

Thanks

mfb
Mentor
In strict language, yes there would be a small jump(due to coulomb potential).
To be small, you need very special nuclei like Tritium.
In general, neutron and proton numbers in a nuclei are so different that the most high-energetic occupied neutron state and the available unoccupied proton states have different quantum numbers.

ChrisVer
Gold Member
hmm... Do for example the higher atomic number mirror nuclei differ much from each other?

mfb
Mentor
Mass of 24Na: 23.99096 u
Mass of 24Al: 23.99994 u
A difference of 8.4 MeV, and this is just the exchange of 2 neutrons <-> 2 protons in a relatively light nucleus. Both decay to 24Mg (23.98504 u), with a half-life of 15 hours (sodium) / 2 seconds (aluminium).

14 MeV decay energy... that's so much the Al sometimes emits a proton or an alpha particle in the process (Isotope list).

To be small, you need very special nuclei like Tritium.
In general, neutron and proton numbers in a nuclei are so different that the most high-energetic occupied neutron state and the available unoccupied proton states have different quantum numbers.
Does it mean that in general, beta decay cannot occur to a ground state of a daughter nucleus, but to such an excited state of the daughter nucleus where the daughter proton is on the orbit vacated by the mother neutron?

Orodruin
Staff Emeritus
Homework Helper
Gold Member
Does it mean that in general, beta decay cannot occur to a ground state of a daughter nucleus, but to such an excited state of the daughter nucleus where the daughter proton is on the orbit vacated by the mother neutron?
This will in general depend on the decaying nucleus. It is very common that beta decay is to an excited state of the daughter nucleus and is followed by gamma emission as the daughter goes to the ground state. In some cases (such as 60Co - 0.12% is still a branching ratio ), the mother can decay into different excited daughter states (meaning different beta energy) resulting in several different gamma lines.

mfb
Mentor
Does it mean that in general, beta decay cannot occur to a ground state of a daughter nucleus
No, and I don't see how you got that idea. A decay to the ground state is always possible. In some cases it is quite unlikely.

but to such an excited state of the daughter nucleus where the daughter proton is on the orbit vacated by the mother neutron?
Often that's not even possible (especially in beta+ decays).