Hubris Meets Hydrogen The Magnetic Moment of

Hubris Meets Hydrogen The Magnetic Moment of the Proton 

When Otto Stern measured the proton moment in the early 1930s, he was advised not to bother—elementary theory proved the result would be one nuclear magneton. Fortunately, Stern had a healthy disregard lor elementary 

Bohr applied a quantum condition to the energy states of the hydrogen atom only certain energy states were allowed. Sommerfeld applied a quantum condition to the orientation of electron orbits only certain spatial orientations relative to an applied magnetic field were allowed. The experiment of Stem and Ger-lach was designed to test Sommerfeld s explanation of the Zeeman effect, namely, the idea of space quantization. 

Stern s experiment was conceptually simple and, as such, it had a beauty all its own. His approach was based on the method of molecular beams. The molecular beam method was originated in 1911 by Louis Dunoyer. In 1921, it was a relatively novel experimental method. Since that time, the molecular beam method has been the basis for an extremely productive line of physical investigation and, as we shall see in future chapters, has yielded both detailed and precise information about atomic properties. In this method, atoms diffuse from a source at one end of a highly evacuated cylindrical chamber, travel a path along the axis of the chamber, and are detected at the other end. Near the source exit, a sue- 

Stem used a beam of silver atoms for his experiment. As the silver atoms streamed toward the detector, they were nudged, at a right angle to their motion, by an applied magnetic field that caused the beam to spread out. Thus, the detector saw a slightly widened beam of silver atoms. The doubters, like Debye, expected the beam atoms to be distributed continuously across the widened dimensions. Stem and Gerlach found something dra- 

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