17. X-Ray Emission & Absorption

OCW Scholar

Session Overview

Modules	Crystalline Materials
Concepts	characterization of atomic structure, Moseley's law, generation of x-rays, x-ray diffraction
Keywords	characteristic emission lines, K_α, K_β, L_α, L_β, atomic spectra, quantized spectrum, continuous spectrum, proton number, atomic number, atomic mass, periodicity, periodic table, x-ray tube, lanthanide series, Moseley's law, screening factor, Bremsstrahlung, braking radiation, ballistic electrons, target anode, cold cathode, hot cathode, scattering angle, Duane-Hunt law, Henry Moseley, William Coolidge
Chemical Substances	calcium (Ca), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), copper (Cu), cobalt (Co), nickel (Ni), zinc (Zn), brass, argon (Ar), potassium (K), tellurium (Te), iodine (I), uranium (U), neptunium (Np), lanthanide series (La-Lu), molybdenum (Mo), lead (Pb), beryllium (Be)
Applications	organization of the modern periodic table, electron-beam welding, lead shielding, analysis of paintings

Prerequisites

Before starting this session, you should be familiar with topics from the first module, Structure of the Atom (Session 1 through Session 7), especially:

Contents and organization of the periodic table
The plum-pudding and nuclear models of the atom
Atomic mass, atomic number, and the sub-orbitals s, p, d, f
The Rydberg equation for energy of photons

Learning Objectives

After completing this session, you should be able to:

Use Moseley's law to calculate the characteristic emission lines of a given element.
Explain the components of a typical x-ray intensity profile, and describe what processes create each component.
Describe how an x-ray tube works, and list 3 applications of x-rays.
Explain why lead effectively absorbs x-rays, and why beryllium effectively transmits x-rays.

Reading

Archived Lecture Notes #5 (PDF), Section 2

Book Chapters	Topics
[Saylor] 7.1, "The Role of Atomic Number in the Periodic Table." (only read until Example 1)	Moseley's discovery of atomic number and its role in the periodic table
[C&S] 1, "Properties of X-Rays."	Electromagnetic radiation; the continuous and characteristic spectrums; production and detection of x-rays; safety precautions

Lecture Video

Flash and JavaScript are required for this feature.

> Download from iTunes U (MP4 - 218MB)

> Download from Internet Archive (MP4 - 218MB)

> Download this transcript - PDF English - US

> Download English - US subtitle (SRT)

Resources

Lecture Slides (PDF - 3.5MB)

Lecture Summary

Shortly after the discovery of x-rays, Henry Moseley investigated the characteristic emission lines of various elements, showing that periodicity follows the proton number Z, not the atomic mass A, producing a modified Rydberg equation with a screening factor for non-hydrogenic atoms. When x-rays irradiate a sample, they scatter off the atoms as well as excite electrons into higher orbitals; this Bremsstrahlung (braking) radiation produces a continuous spectrum underneath the sharp characteristic lines. Modern improvements on the x-ray tube, introduced by William Coolidge, include using a hot cathode and vacuum tube to increase efficiency, water cooling to prevent overheating the anode, and lead (Pb) shielding to absorb x-rays except at the beryllium (Be) windows, which transmit them outward.

Homework

Problems (PDF)

Solutions (PDF)

Textbook Problems

[Saylor] Sections	Conceptual	Numerical
[Saylor] 12.3, "Structures of Simple Binary Compounds."	5, 6	none

For Further Study

Supplemental Readings

Moseley, H. G. J. "The High-Frequency Spectra of the Elements." Philosophical Magazine Series 6 26 (December 1913): 1024-1034.

Heilbron, John Lewis. H. G. J. Moseley: The Life and Letters of an English Physicist, 1887-1915. Berkeley, CA: University of California Press, 1974. ISBN: 9780520023758.