X-rays can reveal structures far smaller than those visible with ordinary light. This lesson introduces their short wavelengths, explains how diffraction provides information about atoms and molecules, and explores key historical discoveries.
X-rays are energetic electromagnetic radiation with wavelengths typically between about 10−8m and 10−12m. When they encounter macroscopic objects, such as teeth, their wavelengths are so short relative to the objects that they act approximately like rays and produce sharp shadows.
All flashcards
X-ray diffraction
Interference of X-rays scattered by a structure, producing a pattern that can reveal structural information.
X-ray crystallography
Using X-ray diffraction patterns from crystals to investigate atomic size, shape, and arrangement.
Bragg's law
The constructive-interference condition for X-rays reflected from crystal planes: mλ=2dsinθ.
Diffraction order m
The positive integer specifying how many wavelengths fit into the path difference between reflected waves.
Rosalind Franklin's contribution to DNA research
She produced X-ray diffraction data that helped Watson, Crick, and Wilkins model DNA's double helix.
Quiz questions
For X-rays reflecting from neighboring crystal planes spaced by d at an angle θ measured from the planes, what is the path difference?Answer: 2dsinθ
A first-order X-ray maximum occurs at θ=18.1∘ for crystal planes spaced by d=0.252nm. Using Bragg's law, what is the wavelength?Answer: Approximately 0.157nm
In the stated Bragg-law convention, how is θ measured?Answer: From the crystal plane surface
In Bragg's law, what does the integer m represent?Answer: The diffraction order
Why can diffraction patterns from a three-dimensional crystal be complex?Answer: Multiple plane families with different spacings and orientations can scatter X-rays.
Based on University Physics Volume 3 by Samuel J. Ling, Jeff Sanny, William Moebs (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.