We describe an undergraduate laboratory experiment in which Bragg diffraction is studied using microwave diffraction from a two-dimensional crystal consisting of a square lattice of metal rods. This apparatus demonstrates the fundamental ideas of the Bragg theory of crystal diffraction using a macroscopic model. Thus, the geometrical relations between the crystal planes and the incoming and scattered wave directions are clearly visible. A key element of the apparatus is a computer interface that allows diffracted intensity measurements at all orientations of crystal and detector. No a priori assumptions need be made concerning the relation between the incident and refracted angles. We also present results of computer simulations of the scattering from our crystal. These simulations have been useful in understanding the differences between the simple Bragg theory and the results from our experiment on a small crystal with finite source and detector distances.

Topics
Crystal lattices, Computer simulation, Crystal optics, Computer interfaces, Laboratories
1.
W. H.
Bragg
and
W. L.
Bragg
, “
The reflection of x-rays by crystals
,”
Proc. R. Soc. London, Ser. A
88
,
428
–
438
(
1913
).
Google Scholar
 
2.
R. G.
Marcley
, “
Apparatus drawing project #6: Bragg diffraction experiment
,”
Am. J. Phys.
28
,
415
–
417
(
1960
).
Google Scholar
Crossref
Search ADS
 
3.
J. J.
Connelly
, Jr., “
Simply constructed atomic stacking models for microwave diffraction experiments
,”
Am. J. Phys.
36
,
559
–
560
(
1968
).
Google Scholar
Crossref
Search ADS
 
4.
W. H.
Murray
, “
Microwave diffraction techniques from macroscopic crystal models
,”
Am. J. Phys.
42
,
137
–
140
(
1973
).
Google Scholar
Crossref
Search ADS
 
5.
G.
Bradley
and
J.
Dewitt
, “
Models for microwave analogs of Bragg scattering
,”
Am. J. Phys.
36
,
920
(
1968
).
Google Scholar
 
6.
R. A.
Allen
, “
Verification of Bragg’s law by the use of microwaves
,”
Am. J. Phys.
23
,
297
–
298
(
1955
).
Google Scholar
Crossref
Search ADS
 
7.
Cenco Model 36811, available from Sargent-Welch, P.O. Box 5229, Buffalo Grove, IL 60089-5229 and 〈www.sargentwelch.com〉.
8.
Model NI PCI-6014, National Instruments Corp., 11500 N. Mopac Expressway, Austin, TX 78759-3504 and 〈www.ni.com〉.
9.
R. W. P. King and T. T. Wu, The Scattering and Diffraction of Waves (Harvard Press, Cambridge, MA, 1959).
This content is only available via PDF.
© 2004 American Association of Physics Teachers.
2004
American Association of Physics Teachers
AAPT members receive access to the American Journal of Physics and The Physics Teacher as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.