The XRays bounce. That's all that half of a high school education has taught me, I hope it helps.

How in-depth do you want to go?

Basically, it explains how X-Rays will scatter off a crystal structure.

It's somewhat similar to the more common Snell's Law, which explain why your hand looks to go off at an angle when you place it in water.

"The interference is constructive when the phase shift is a multiple of 2π; this condition can be expressed by Bragg's law."

This is the key. Looking at the 3rd from the top wikipedia diagram that shows you the easily derived length

dsin(theta). What is special about this length?

This is half the "extra distance" that the bottom beam travels to reach whatever target is shown (on the scale we're dealing with both lines hit the same "effective" point in the eye/reciever/target.

so 2*dsin(theta) is ALL the extra distance that the bottom beam travels.

Why do we care? Well we know that if the top and bottom beams are "in phase" when they reach their target you will have constructive interference, i.e. an increase in intensity at the target.

When will two beams be in phase? If their peaks or troughs line up (i.e. their phase = 2*Pi).

When does this occur? if the extra distance one beam travels (2*dsin(theta)) is exactly one wavelength (lambda) longer than the other.

Or if 2dsin(theta) is 2 wavelengths longer... or 3, 4, 5 all the way to infinity (represented by n)

ergo, if 2*dsin(theta) = n*lambda you will have constructive interference.

If that's still too rough, just remember the general condition for constructive interference in a straight line.

n*lambda = x

where x is distance. Waves will interfere constructively at any x that is an integer multiple of the wavelength.

This is just a slightly more complicated case, where you substitute in 2*dsin(theta) for x because there is a reflection occuring.

nλ = 2 sinΘ

λ = the wavelength of an x-ray

d= the spacing of the crystal layers (path difference)

Θ= the incident angle (the angle between incident ray and the scatter plane)

n= integer

Yes to what abgemacht and YJ said.

X-ray diffraction (wave interference) is used to study the structure of molecules, often crystals.

This one I find helpful:
http://www.mrl.ucsb.edu/mrl/centralfacilities/xray/xray-basics/index.html

.... and I even managed to get daggers in the equation... :)

Really the only point of confusion in what TheWizard said is that "d" is not always clear, as these particles are not true point-sources, but have their own wavelengths as well.

You mean physics takes place off of a chalkboard? Quit making shit up abge.

This is cool stuff I will have to come back, I need an afternoon nap,
I have just been surfing and got pounded, got some good waves, but the second wave
I went for drilled me, held me under and delivered a full rinse cycle, sweet !!!!

The name Bragg caught my attention, there were 2 Braggs a father and son,
and I think both had a long association with Adelaide University, the physics lab
buildings are named after one (or both ) of them.

I like the old uncertainty principle, is it Heisenburg's about the uncertainty in position of a moving particle or object & some vague reference to an associated De Broglie
wavelength has popped up from my subconcious
I need a nap (& a good head job but I can tee that up thank you all )

@Major

Yes, this is the same father & son duo.

What exactly are you asking about the uncertainty principle? It is commonly referred to as Heisenberg's. It says that the uncertainty of position and uncertainly of momentum multiplied together can not be less than hbar/2.

lol MM, your 1st paragraph almost stands as an analogy to Bragg's law. Not sure if that was deliberate or not. Exceedingly clever if so.

Heisenberg states that as you reduce the uncertainty in position or a particle, the uncertainty in momentum increases (or vice versa)

What YJ said. It is literally just doing a little geometry while keeping in mind that the "goal" is to have everything in phase.

Hey, thanks everyone. I'm an economics and history guy, so I don't know what the fuck you guys are talking about. But my roommate and gf seem to have found whatever gibberish you all posted here pretty helpful, so much thanks.

That being said, it does sound like some pretty interesting stuff. Maybe I'll read into it a little more tomorrow.

Thanks again.

Re: the hand looking angled under water. Isn't that just light refraction due to the desnity of the water being different from the air? I mean, refactive and reflective properties are what ray-tracing software uses and different crystals have different refractive properties due to the various elements and their density, just like water. Or is that, in essence, what these two laws actually explain and "refraction" is something akin to centrifical force, which is to say a non-existent force in scientific terms because it is actually the idea that an object in motion will stay in motion unless acted upon by an external force, in the case of a centrifuge, the wall.

@Draug

It happens because air and water have different indexes of refraction, which, in part, is due to density.

My point is just that both Snell's and Bragg's laws describe how EM waves react for different boundary conditions.

""refraction" is something akin to centrifical force, which is to say a non-existent force in scientific terms"

No, I wouldn't say that. Refraction is a real thing that happens to EM waves based upon changes in medium.

Just to prevent confusion:

Clearly X-Rays and crystal structures are different than light and water because light still passes through the water, whereas X-Rays bounce off the crystal structure. But, the principle is exactly the same. The only difference is what 2 mediums you're using and what frequency you're working with.

Yeah abge I think the snell's law analogy wasn't the greatest because the medium isn't changing. Agree with everything else you've said.