Could one preserve polarized neutrons from decaying with a high B-field?

[francois lamarche]

TL;DR

Since the magnetic dipoles of neutrons and protons are different, they have different energy shifts in a strong magnetic field. How strong of a magnetic field would you need to affect the rate of decay of neutrons into protons?

I have to yet done the order-of-magnitude calculation yet, but I suspect it will be thousands of Testlas... But maybe one could already see some effect with a weaker field?

 

[snorkack]

TL;DR Summary: Since the magnetic dipoles of neutrons and protons are different, they have different energy shifts in a strong magnetic field. How strong of a magnetic field would you need to affect the rate of decay of neutrons into protons?

I have to yet done the order-of-magnitude calculation yet, but I suspect it will be thousands of Testlas... But maybe one could already see some effect with a weaker field?

I suspect it is not possible.
It would be many more orders of magnitude, but not even that would work.

p has NMR frequency of 1 GHz at 23,5 T.
n´s gyromagnetic ratio is a bit under 70% that of proton
Note that this under 700 MHz is the split both ways from the energy level in absence of field. The shift in n-p energy spread would be just a but over 15 % of the full resonance frequency of proton, or about 6,5 MHz/T

1 eV would correspond to 242 THz, or 1240 nm, in near infrared. Which seem to means that the NMR resonance frequencies of nuclei would go to a few eV - visible light - in MT range, and into MeV, the range of hard γ rays and nuclear reactions, in TT range.

But the problem with it is ESR. Electron also has gyromagnetic ratio (much bigger than that of nuclei). If the magnetic field shifts the energy levels of proton and neutron, it would also shift the energy level of the electron to form by beta decay... and it would shift the two electron spin states in opposite directions. Then applying a strong field would always favour beta decay to one of the electron spin direction. I don´t quite see how to block beta decay to favourite electron spin, but maybe someone else knows restrictions there.

 

[Vanadium 50]

Magnetic fields do no work.

 

[francois lamarche]

I suspect it is not possible.
It would be many more orders of magnitude, but not even that would work.

p has NMR frequency of 1 GHz at 23,5 T.
n´s gyromagnetic ratio is a bit under 70% that of proton
Note that this under 700 MHz is the split both ways from the energy level in absence of field. The shift in n-p energy spread would be just a but over 15 % of the full resonance frequency of proton, or about 6,5 MHz/T

1 eV would correspond to 242 THz, or 1240 nm, in near infrared. Which seem to means that the NMR resonance frequencies of nuclei would go to a few eV - visible light - in MT range, and into MeV, the range of hard γ rays and nuclear reactions, in TT range.

But the problem with it is ESR. Electron also has gyromagnetic ratio (much bigger than that of nuclei). If the magnetic field shifts the energy levels of proton and neutron, it would also shift the energy level of the electron to form by beta decay... and it would shift the two electron spin states in opposite directions. Then applying a strong field would always favour beta decay to one of the electron spin direction. I don´t quite see how to block beta decay to favourite electron spin, but maybe someone else knows restrictions there.

Thanks... I realized it would take PetaTeslas... and then I realized I had not thought about how the electron split played into it - very good answer.

 

[Vanadium 50]

Here's why this won't work.

Magnetic fields do no work. So you will not be in a position for any blocking due to the electron's motion. If you want to have this a consequence of the electron's spin, you have two problems. One is that the mass difference is greater than 2m(e), so if you tried to create a field this strong, you would simply pop e+ e- pairs out of the vacuum (a process called "vacuum sparking".) The other problem is that you can always flip the spin of an electron through the emission of a photon.

With electric and color fields you can do this, but not with free neutrons. if you have a neutron in a nucleus, you can energetically block all the possible decay channels. This is why a neutron in a deuterium nucleus is stable: if it becomes a proton, it is sitting right next to another proton, and this is energetically impossible.