Equipment List:
Pasco Microwave Optics including the mock crystal cubes and rotating table.

Purpose:
To calculate the 100 plane spacing in a mock crystal using Bragg diffraction.

Introduction:
See page 1011 of  Halliday, Resnick, and Walker's 7th edition.
See this link: Bragg Diffraction

Procedure:
Set up your equpiment and get it working properly.

Data:
Remember you are trying to record the grazing angle not the angle of incidence to the normal as is more common.
Remember ALL your data must always be taken where the angle of the transmitter is the same as the angle of the reciever. The receiver is always to measure the relected beam from the transmitter and as such, those two angles (incident and reflected) must be the same. For this reason, after starting out with the transmitter and receiver directly facing each other (with the cube in between), you proceed to take the data by moving the tranmitter (it has the longer electrical cord) TWO degrees and then the rotate the crystal in the same sense but only by ONE degree. This will ensure that your reciever is always measuring the reflected angle from the transmitter of the 100 plane. Take between sixty and seventy data points.

 

Anaysis:
Graph the intensity versus grazing angle; use the computer. Your will find two orders (m=1, m=2) for which there are maxima. The first order maximum will be the largest of the graph. The second order maximum will be much smaller. There will be other minor maxima from errant reflections. Find the angle of the first and second maxima from your graph and calculate the spacing. Compare to a direct measurement with a ruler or vernier calipers. If all goes well, you could get a one percent discrepancy; more than ten percent and something may be wrong.