# Homework Help: Bragg's Angles for X-Ray

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1. Jan 24, 2017

### transmini

1. The problem statement, all variables and given/known data
The Spacing between the Na and Cl atoms in table salt (NaCl) is $d=2.82x10^{-10}m$, which was first deduced from Bragg scattering. For an experiment where X-rays of energy 20 eV are produced, what are the corresponding Bragg angles below $90^{\circ}$ for scattering from a large crystal of table salt?

2. Relevant equations
Bragg's Law: $2dsin(\theta)=n\lambda$

3. The attempt at a solution
$sin(\theta)=\frac{n\lambda}{2d}$
$\lambda = \frac{hc}{E_{photon}}$
$\theta = sin^{-1}(\frac{nhc}{2dE})$
$\theta = sin^{-1}(\frac{n*1240eV\dot nm}{2*0.282nm*20eV})$
$\theta = sin^{-1}(n*109)$

but this isn't within the domain of arcsin. So are there just no Bragg's angles here? Or is there a different energy that I'm using rather than 20 eV?

2. Jan 24, 2017

I believe your calculations are correct. Perhaps someone else can also check the numbers, but I think the x-ray energies need to be more like 20 keV.

3. Jan 25, 2017

### mjc123

Definitely in the keV region. From memory, Cu Kα, a common source, is around 8 keV.

4. Jan 25, 2017

### transmini

After turning in the work today, the professor mentioned there was a typo in the book and he failed to email us to tell us that before hand. It was in fact supposed to be 20 keV.