Can an electron emit a single photon without violating conservation laws?

[cragar]

Someone told me that an electron can't emit a single photon because
it would violate conservation of momentum and energy.
I thought about cyclotron radiation. Let's say an electron is being bent in a B field
so it starts to radiate, can't we just say that this momentum and energy came from the
B field.

 

[andrien]

it is the free electron which can not emit photon.Under the action of potentials,it will like in bremmstrahlung(spelling may be wrong) it does get accelerated and it radiates.In case of magnetic field,when charge particle is there.It will emit radiation, it is particularity of what is called synchrotron radiation.Just google to find out more on this.

 

[sophiecentaur]

If an electron is having its path bent by some external field, there must be (relatively) massive piece of equipment involved so the electron is not actually 'isolated'. A photon of bremmstrahlung radiation will have momentum but the whole of the electron plus accelerating kit could be regarded as sharing the momentum that's exchanged.