# Soft X-rays

1. Jul 12, 2014

### Entanglement

what is the reason of soft x-rays, Is it because when a accelerated electron approaches an atom the electrons' electric field repel the incoming electron causing deceleration and also i scattering could be a reason when the electron approaches the nucleus, is that correct?
what is the relation of the number and energy of photons emitted to the rate of its deceleration, how can it be calculated? Big to PF, and thanks in advance!

2. Jul 12, 2014

### UltrafastPED

"Soft x-rays" have less energy than "hard x-rays". The traditional method for making x-rays was to accelerate electrons through a fixed potential - call it V - so that every electron has the same energy; about eV in this case.

Then collide the electrons with a thin metal film. If the electron energy is sufficient, then the "characteristic x-rays" for that metal will be emitted.

"Hard" x-rays are more penetrating.

See https://en.wikipedia.org/wiki/X-ray_generator

3. Jul 12, 2014

### Newtonsstudent

Last edited by a moderator: May 6, 2017
4. Jul 13, 2014

### Entanglement

Thanks a lot for your answer, but I don't think you understood my question correctly

5. Jul 13, 2014

### davenn

6. Jul 14, 2014

### UltrafastPED

Maybe can work you some question so it clearer be.

7. Jul 14, 2014

### rigetFrog

Yeah, clearer question would help.

Soft x-rays are typically generated at synchrotrons and wiggling the electron beam using an undulator.

8. Jul 14, 2014

### Entanglement

I mean I know that when an electron falls from a higher level it emits a photon of energy hv,
What is the equivalence of that for decelerating electrons, what governs the number of photons and the energy of each photon??

9. Jul 14, 2014

### rigetFrog

The undulator produces a magnetic field that acts on the electron beam (http://en.wikipedia.org/wiki/Undulator).

A magnetic field has a potential energy similar to a (quantum) harmonic oscillator along one axis (Introductory Quantum Mechanics, Liboff 4th editon).

I'm guessing the transitions are harmonic oscillator type transitions, with higher energy and lower energy states available.

10. Jul 15, 2014

### davenn

The maximum energy of the produced X-ray photon is limited by the energy of the incident electron, which is equal to the voltage on the tube times the electron charge, so an 80 kV tube cannot create X-rays with an energy greater than 80 keV

Dave

11. Jul 15, 2014

### UltrafastPED

For braking radiation, conservation of energy tells us that the total energy released as photons cannot exceed the total energy of the initial source.

An x-ray passing through matter will have multiple interactions, all electromagnetic, knocking off electrons as it goes. These electrons will in turn generate additional photons - a chain reaction - but with ever lower energies in the photons, and in the electrons.

For some calculations see http://www.astro.utu.fi/~cflynn/astroII/l3.html
and http://whs.wsd.wednet.edu/faculty/b...onphysics/lecturenotes/chapter7/chapter7.html

12. Jul 15, 2014

### davenn

its so much fun being ignored

13. Jul 15, 2014

### UltrafastPED

It's my favorite activity! :tongue:

14. Jul 16, 2014

### Entanglement

Thanks guys I got it.

15. Jul 16, 2014

### Entanglement

What do you mean?

16. Jul 16, 2014

### UltrafastPED

That was for me, so you can just ignore it.