neutrinos (1 Viewer)

[sasquatch]

Im a bit confused as to why neutrinos were necessary in terms of what jacaranda states. They explain the need for neutrinos in terms of the varying energies exhibited by the beta particles emitted during the beta decay process.

Excel explains it in terms of a break down in the conservation of energy as to why neutrinos were necessary.

Why are the explinations different from each other?

 

[alcalder]

These explanations may seem different, but in fact describe the very same thing. Physics in Context explains it well, I think.

In my own words...

During beta decay, they measured the kinetic energy of all the emitted beta particles and graphed them on an Energy versus No of electrons graph. They found that beta particles were emitted at a variety of energies and the graph was a smooth line (ie there was a continuum of energies at which the beta particle could be emitted).

"Then they compared the mass of the original nucleus with the sum of the mass of the product nucleus, the mass of the beta particle, plus their kinetic energies." (Physics in Context) The Law of Conservation of Energy did not hold.

They then looked at the Law of Momentum and Law of Conservation of Electron Spin, and these rules seemed broken as well (some mass was lost and some electron spin was gone).

There had to be another particle that took away some energy, mass and electron spin - hence the need for the neutrino (for positron decay) and antineutrino (for beta decay).

 

[sasquatch]

yeah well i thought they would have to link, but jacaranda didnt really mention anything about the law of conservation of energy and momentum in its explination. thanks. could you possbily read my answer to the dot pot

"6. Discuss Pauli’s suggestion of the existence of the neutrino and relate it to the need to account for the energy distribution of electrons emitted in β-decay."

• The neutron was able to explain the composition of the nucleus, but problems in explaining beta decay still existed.
• It is impossible for an electron to be confined to a nucleus, and thus beta decay could not be explained as it appeared to involve the emission of an electron from a nucleus.
• Reasons for electrons not being able to occupy the nucleus is that, atomic masses could not be explained in terms of electrons and protons and the de Broglie wavelength of an electron would be much greater than that of the radius of the nucleus.
• Alpha particles emitted from similar nuclei had the same energy, but beta particles would be emitted with a range of energies.
• This indicated that the conservation laws were not abided due to the varying energy of the beta particles.
• To explain the break down in the conservation of energy involved in the beta decay process, Pauli predicted that another sub-atomic particle (the neutrino) must exist.
• The masses before and after the beta decay process were measured and the difference would have to have been converted into a form of energy (due to Einstein’s .
• The electron emitted in the beta decay process was found to have less energy than required to ensure the conservation of energy.
• Gamma rays were predicted to account for this energy loss but could not be detected.
• Pauli suggested that this missing energy was carried away by a neutrino.
• The type of neutrino associated with beta minus decay, is actually an antineutrino as its properties tend towards classification as an anti-particle.
• Now that such a particle was identified, beta minus and beta plus decay could now be explained in terms of neutrinos and anti-neutrinos.

I wrote this before your answer, so i dont know if it covers enough. Thanks.

 

[alcalder]

• It is impossible for an electron to be confined to a nucleus, and thus beta decay could not be explained as it appeared to involve the emission of an electron from a nucleus.
• Reasons for electrons not being able to occupy the nucleus is that, atomic masses could not be explained in terms of electrons and protons and the de Broglie wavelength of an electron would be much greater than that of the radius of the nucleus.

I would check this bit ^

proton = neutron + positron

neutron = proton + beta particle

Thus the "electron" is being confined in the nucleus as part of the nucleon.

 

[sasquatch]

i dont get what you mean?

 

[alcalder]

OK, is there a reference for that first bit you talk about - it is impossible for an electron to be confined to the nucleus?

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What I am saying is that when there is positron decay a proton is decaying to a neutron (that remains in the nucleus) and positron (and neutrino) and when there is beta decay, a neutron is decaying to a proton (that remains in the nucleus) and beta particle.

There would need to be the question, then, if

neutron = proton + beta particle

AND

proton = neutron + beta particle (electron)

the mass equations don't work without considering Einstein and E=mc² and binding energy. But also, there was energy lost and this is what the neutrino takes away. The neutrino has zero rest mass.

That's probably gobbledegook, is it?

 

[sasquatch]

I understand what your saying, but i dont get what it has to do with what i wrote. I was saying that with beta-decay (beta-minus decay) it appeared an electron was being emitted from the nucleus (as if electrons occupied the nuclues). But then if this was true, from compositions of electrons and protons existing in the nucleus would not account for the measuerment of the mass of the nucleus. Also the de Broglie wavelengths of the electrons would be greater than that of the size of the nucleus which would not make sense. This indicates that the electron is not actually a component of the nucleus.

What your talking about beta-decay, was discovered after Pauli's proposal of the neutrino. Fermi proposed that in beta-minus decay, a neutron of the nucleus decayed into a proton, electron and a antineurino (where the proton remained in the nuclues, and the electron and antineutrino were emitted) and in beta-plus decay, a proton of the nucleus decayed into a neutron, positron and a neutrino (where the neutron remained in the nucleus, and the positron and neutrino were emitted).

My statement didnt say that electrons werent emitted from the nucleus, it just stated that electron were not a composition of the nucleus.