# Energy of scattered photon

1. Oct 26, 2004

### nelufar

How to calculate energy of scattered photon when the energy of incident photon is equal to the rest energy of an electron and the angle between the direction of the recoiling electron and the incident photon is 40 degrees?
In compton effect the energy of scattered photon is related to angle
between the scattered photon and the incident photon. How to relate the angle between the direction of the recoiling electron and the incident photon and angle between the scattered photon and the incident photon?

2. Oct 26, 2004

### Pieter Kuiper

Derive this from conservation of energy and momentum in relativistic mechanics. Or look it up. I know it is on HyperPhysics.

3. Oct 26, 2004

### nelufar

Can't we use derivation for Compton effect?

4. Oct 26, 2004

### Pieter Kuiper

5. Oct 28, 2004

### nelufar

I tried solving the problem using relativistic approach but there also the relation is for angle of the scattered photon not for angle of recoiling electron.So,can there be any other way to solve it.

6. Oct 28, 2004

### Pieter Kuiper

Momentum is conserved. The transverse component was zero before the interaction, so theta and phi are related by
$$0 = \frac{h}{\lambda '} \sin \theta - p_e \sin \phi$$

7. Oct 28, 2004

### nelufar

But we only know the energy of the incident photon and rest mass of electron. Recoiling electron will also have energy which is not given.So how to calculate P_e and what about /theta?

8. Nov 1, 2004

### nelufar

Is there no solution to the problem? Can there be any other approach to solve it?

9. Nov 1, 2004

### Pieter Kuiper

This looks like a homework problem, so of course there is a solution.
You just need to work on it a bit.

10. Nov 1, 2004

### nelufar

I have tried a lot but the equation which you have provided, I got stuck there. So, if you can help , it would be really helpful. Atleast tell me can there be some other approach which probably I am not thinking of.

11. Nov 1, 2004

### Pieter Kuiper

I referred you to HyperPhysics. Momentum is conserved so
$$\vec{p_i} = \vec{p}_f + \vec{p_e} \Leftrightarrow \vec{p}_f= \vec{p_i}-\vec{p_e}$$

$$p_f^2 = p_i^2 + p_e^2 - 2\ p_i\ p_e \cos{\phi}.$$
That is how you can get it as a function of the electron angle, I think.
If you now proceed along similar lines as Nave, I think you should get there.

Last edited: Nov 1, 2004
12. Nov 1, 2004

### nelufar

Thanks. I will try with this.