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Argos
2004-Mar-03, 03:26 PM
I think this is tangentially related to astronomy, so I ask the fellows some help in clarifying my doubts on the issue:

Electrons (or positrons) are accelerated within synchrotrons [or around stars and other powerful magnetic fields]. They emit (synchrotron) radiation, photons, tangentially all along the circular orbit while traversing gaps of bending magnets.

Does the direction of emission of the photons influence their observation? I mean, do I have to be positioned right in the tangent, on the same plane as the syncrotron´s ring, to observe the photon (or capture it with a device), or will the wave associated to the photon propagate in all directions, making it possible to observe the photon from all points of vantage (say, from above the synchrotron´s ring)?

The same goes for electron scattering: electrons emit a photon when submitted to a change of direction of motion resulting from a collision with another electron or photon. The resulting photon is emitted in a given direction. Do I have to stand along the line of emission to see the photon (or record it with an instrument), or, again, will the wave propagate in all directions, allowing for observation from everywhere?

(*) I hope having been clear enough with my poor English.

Ut
2004-Mar-03, 04:52 PM
The short answer to your question is "Yes".


The radiation is concentrated in the direction of the electron's motion and is strongly plane-polarized.

For relativistic synchrotron emission, the photons are given off within a rather compact beam. If the Earth/detector is within the region passed over by that beam at some point in the electrons cycle, we will see blinking. From a single electron, anyway.

Bremsstrahlung radiation is a little different. Light can be given off in random directions due to multiple interactions.

swansont
2004-Mar-03, 06:05 PM
The short answer to your question is "Yes".


The radiation is concentrated in the direction of the electron's motion and is strongly plane-polarized.

For relativistic synchrotron emission, the photons are given off within a rather compact beam. If the Earth/detector is within the region passed over by that beam at some point in the electrons cycle, we will see blinking. From a single electron, anyway.

Bremsstrahlung radiation is a little different. Light can be given off in random directions due to multiple interactions.

But is it still perpendicular to the acceleration vector? It's the same fundamental process - you accelerate a free charge and it radiates.

Jason Thompson
2004-Mar-03, 10:08 PM
Does the direction of emission of the photons influence their observation? I mean, do I have to be positioned right in the tangent, on the same plane as the syncrotron´s ring, to observe the photon (or capture it with a device), or will the wave associated to the photon propagate in all directions, making it possible to observe the photon from all points of vantage (say, from above the synchrotron´s ring)?

A device can only 'see' a photon when it arrives at that device, so therefore yes, you do have to be in line with the emission to detect it. Consider the photons that make a laser beam. You cannot see the beam itself, only the spot it makes on the object it is aimed at, i.e. you cannot see the photons emitted by the laser until they bounce off something else so they are travelling in a direction that takes them to your retina (or some git turns the laser into your face!).

Wiley
2004-Mar-04, 12:03 AM
But is it still perpendicular to the acceleration vector? It's the same fundamental process - you accelerate a free charge and it radiates.

Yes. The direction of the photons is in the direction of the velocity of the charge, which for synchrotron radiation is perpendicular to the acceleration.

Argos
2004-Mar-04, 03:19 PM
Thank you all folks. :D

Just another nitpick:



Bremsstrahlung radiation is a little different. Light can be given off in random directions due to multiple interactions.


Light is emitted in random directions, but you just can see the photons that come towards you, at each interaction, right?