Alpha decay and magnetic fields

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Discussion Overview

The discussion centers on the effects of external electromagnetic fields, particularly magnetic fields, on the alpha decay of nuclei. Participants explore theoretical implications, potential influences on tunneling processes, and the relevance of environmental conditions in various astrophysical contexts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how alpha decay is influenced by external electromagnetic fields, specifically regarding the WKB method and tunneling effects.
  • Another participant expresses skepticism about the significance of magnetic fields, suggesting that the energy scales involved are too small to have a notable effect on alpha decay.
  • Some participants argue that while magnetic fields can influence electronic configurations, their direct impact on the tunneling time of alpha particles remains uncertain.
  • There is mention of high magnetic fields in astrophysical environments, such as stars and supernovae, but participants note a lack of evidence for changes in alpha decay under these conditions.
  • Concerns are raised about the randomness of alpha emission and whether it is influenced by environmental conditions, leading to further questions about the relationship between magnetic fields and tunneling processes.
  • One participant states that while the effect of magnetic fields on alpha decay is non-zero, it is too small to be significant, comparing it to the negligible gravitational influence of distant celestial bodies.
  • Another participant introduces the concept of Zeeman splitting and its potential impact on alpha energy and tunneling rates, but emphasizes the extreme magnetic field strengths required to observe substantial effects.
  • Discussion includes the possibility of nuclei existing in extreme environments, such as magnetars, and how these conditions might affect alpha decay processes.

Areas of Agreement / Disagreement

Participants express a range of views, with some skeptical about the impact of magnetic fields on alpha decay, while others propose that there may be subtle effects under specific conditions. No consensus is reached regarding the significance of these influences.

Contextual Notes

Participants note limitations in the current understanding, including the dependence on specific conditions and the lack of empirical evidence for changes in alpha decay rates in high magnetic fields.

andresB
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How is the alpha decay of a given nucleus affected by the presence of an external electromagnetic field?

It's probably an easier question that I think but I've been unable to find a treatment of the tunneling of the alpha particle using WKB method in the presence of a magnetic field.
 
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andresB said:
How is the alpha decay of a given nucleus affected by the presence of an external electromagnetic field?
I don't think it is?
 
I don't see any setup where a magnetic field would be strong enough to have any notable effect. The energies involved in the magnetic field are 600 neV/Tesla, the strongest permanent magnetic fields we can generate are about 100 T, and typical alpha decay energies are in the MeV range. You can get higher fields in crystal lattices, but not that much higher.
 
I don't know if a magnetic field would have, by itself**, an effect at all the WKB tunnelling time but I've also not seen a proof or an argument that say it doesn't.

(**I say by itself because a magnetic field can affect the electronic configuration around the atom and in that way affect the potential the alpha particle have to tunnel, but I'm not interested in that effect at the moment).

But Well, in stars there are quite high magnetic field even bigger that the so called critical field of QED yet I can't find any reference to a change in the alpha decay for thiese high fields (my search prowess is not that good, though)
 
andresB said:
But Well, in stars there are quite high magnetic field even bigger that the so called critical field of QED yet I can't find any reference to a change in the alpha decay for thiese high fields (my search prowess is not that good, though)
Not in normal stars, not even in neutron stars. In doubt, supernovae have stronger everything than everything else, but I still don't see where fields that strong would come from. But even with 4.3 GT you still get just a few keV. Spin orientations of everything would depend on the magnetic field of course.
 
mfb said:
Not in normal stars, not even in neutron stars. In doubt, supernovae have stronger everything than everything else, but I still don't see where fields that strong would come from. But even with 4.3 GT you still get just a few keV. Spin orientations of everything would depend on the magnetic field of course.

So isn't alpha emission a random process [on which I based my initial answer with questionmark] but it depends on the environmental conditions?
 
That does not exclude each other.

Alpha particles as even-even nuclei don't care about spin anyway.
 
So, mfb, you are saying that if I have a nucleus and switch on a magnetic field (even a strong field) the effect of these field will be very small because the energy related to it is very small?. why the small value of the energy of the magnetic field matters that much?
 
In the end I thing the real question I'm interested is why a magnetic field would not change the wkb calculation for the tunnelling time.
 
  • #10
andresB said:
why the small value of the energy of the magnetic field matters that much?
What else would influence anything? The tunneling is given by the potential, and this potential gets some tiny deviation from the magnetic field. It gets velocity-dependent, but I plugged in the speed of light so this is a very conservative overestimate already.
 
  • #11
andresB said:
but I've also not seen a proof

The effect is non-zero. The effect is also far, far too small to see. So you won't find a proof that it's identically zero, because it's not. But it is so small we don't worry about it, just like we don't worry about the gravity of Pluto when calculating the trajectory of a baseball.

mfb said:
Alpha particles as even-even nuclei don't care about spin anyway.

True, but the parent nuclei do. U-235 has a magnetic moment of about 0.3 nuclear magnetons, and Th-231 must have a magnetic moment of similar magnitude (although I can't seem to find it). Put them in a magnetic field and the Q value will be shifted by the Zeeman splitting (about 10-8 eV/T) and thus the alpha energy and in turn the tunneling rate. But since alphas are 5 MeV, you need to be in the 100 gigatesla range to see a substantial effect. You can get fields close to this in magnetars. Unfortunately, you don't have nuclei any more in magnetars.
 
  • #12
The surface could have a thin layer of nuclei. The rapid rotation should mean they see a mixture of electric and magnetic fields.
 
  • #13
Vanadium 50 said:
But since alphas are 5 MeV, you need to be in the 100 gigatesla range to see a substantial effect. You can get fields close to this in magnetars. Unfortunately, you don't have nuclei any more in magnetars.
Um? Pressure and density drop to zero on surface of neutron star. Magnetic field does not.
 

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