Stern–Gerlach experiment?

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If I shoot a beam of neutrons into a non-uniform E field will they get deflected because of their spin or do we need a B field.
 

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  • #2
Meir Achuz
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A B field is needed.
There could be a small effect in an E field which could polarize the neutron, like the deflection of a neutral molecule in an E field. I think this is so small it has never been seen experimentally, and would not depend on spin.
 
  • #3
DrDu
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Similar effects depending on spin are at least observed for electrons moving in electric field gradients (very hype now under the name spintronics), so I would assume that they are also present in neutrons.
 
  • #4
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A B field is needed.
There could be a small effect in an E field which could polarize the neutron, like the deflection of a neutral molecule in an E field. I think this is so small it has never been seen experimentally, and would not depend on spin.
What do you mean by polarize a neutron? And could we bring relativity into the mix, where we had a line charge in one frame at rest, no current. But then we had a neutron moving down the wire and a second observer moving in the other way so he sees a current and a B field. Would this observer witness a deflection based upon the spin of the Neutron?
 
  • #5
SpectraCat
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If I shoot a beam of neutrons into a non-uniform E field will they get deflected because of their spin or do we need a B field.
You actually need a B-field *gradient* to generate a force on the magnetic dipoles, so your field needs to be inhomogeneous, like in the SG experiment.

[EDIT: I am not sure about the inhomogeneous E-field ... It seems that a neutron moving through an inhomogeneous E-field should experience a weak B-field interaction as well, but I am not completely certain that is correct. Whether or not the B-field (if any) experienced by a neutron in such a case is large enough to observe a measurable deflection is yet another question.]
 
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  • #6
SpectraCat
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A B field is needed.
There could be a small effect in an E field which could polarize the neutron, like the deflection of a neutral molecule in an E field. I think this is so small it has never been seen experimentally, and would not depend on spin.
Again, neutral molecules are not deflected by E-fields, but by E-field gradients. The angular momentum of a dipolar molecule will be perturbed by a homogeneous E-field, and in the strong field limit the dipole will align along the field direction. However you need a field-gradient to change its momentum.
 
  • #7
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A particle moving in an E-field feels a B-field in its rest frame, so there should be an observable effect.
 
  • #8
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interesting thanks for your answers. Does a particle having spin imply it has a magnetic moment? Or when the particle gets deflected in a non-uniform B-field, is this because it has spin or a magnetic moment?
 
  • #9
DrDu
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thanks for the link I will start reading it.
 

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