# Why-Hydrogen has small

1. Apr 24, 2005

### System Engineer

Can any one explain physically why the scattering factor is small for back reflection in case of hydrogen i.e (theta=pi/2).

Any help ..Thanks
Ess ESS

2. Apr 25, 2005

### Chronos

Simplest atom [one proton, one electron]?

3. Apr 25, 2005

### dextercioby

What particles are u sending towards the H atoms...?

Daniel.

4. Apr 25, 2005

### System Engineer

Well the problem does not say anything about whats being sent towards the Atom.

5. Apr 25, 2005

### dextercioby

If u know a bit about Rutherford scattering,then u'll figure out the answer yourself.

Daniel.

6. Apr 25, 2005

### ZapperZ

Staff Emeritus
Whenever you are asking something like this, it is important that you first of all, quote the EXACT "problem" that you are being asked. Your interpretation of what it is asking may be wrong or misleading, so never ever just reveal your interpretation of what is being asked.

Secondly, I have no clue on what "theta" is in your original post, nor did you care to define it. What is this? What is it measured FROM? Seems that theta=pi/2 is 90 degree scattering. So why would this correspond to "back reflection"?

So now can you see why, as it stands, this whole thing is very vague and strange?

Zz.

7. Apr 25, 2005

### System Engineer

Sorry for my Ignorance...I apologise.
Here is the Complete problem
"The electron density in a hydrogen atom in its ground state is spherically symmetric, and is given by

p(r)=exp{(-2r/a)/(pi*a^3)

where a, the first Bohar radius has the value 0.53 Angstrom. Compute the atomic scattering factor for hydrogen and plot it as a fucntion of =2ksin(theta)=4*pi*sin(theta)/lambda.

Explain physcially why the scattering factor is small for back reflection (theta=pi/2).

I have solved the first part but i am unable to find an explanation for the second part.

Hopefully now u can be of help.

Thanks
Ess ESS