© Left: Wikimedia Commons, Creative Commons Attribution 3.0 Unported License. Author: Jan Ainali, 12 February 2008. Right: NIH.
On the left is a magnetic resonance imaging (MRI) apparatus in a hospital setting. Superconducting current flows produce the very high, sustained magnetic fields required to use the spins of protons in human tissue to create images like the brain scan on the right. Magnetic fields are easily generated from an electric current, but the current required for efficient MRI scanning generates a tremendous amount of heat. The solution is to use superconducting magnets, in which electric current can flow without resistance. The electrons in a superconductor are in a macroscopic quantum state that we will learn about in this unit and in Unit 8. As we delve further into the unit, the concept of spin, electrons, protons, and neutrons will come to play a crucial role in our understanding of the possibility of creating macroscopic quantum states, as well as for their dramatic use as a medical diagnostic tool. (Unit: 6)