One promising weapon in the battle against cancer is fast-neutron therapy in which a beam of high-energy (hence, fast) neutrons is directed into a cancerous region (here at the laser cross hairs). High-energy neutrons break bonds in the DNA of the cancer cells, causing the cells to die and thus eliminating the cancer. You can produce a beam of high-energy particles by using an electric field along a long path if the particles are charged. A long-enough path is not available in a hospital, however, and neutrons are not electrically charged.
How can a beam of high-energy neutrons be produced?
The answer is in this chapter.
As we have discussed, one major goal of physics is the study of how an electric field can produce an electric force on a charged object. A closely related goal is the study of how a magnetic field can produce a magnetic force on a (moving) charged particle or on a magnetic object such as a magnet. You may already have a hint of what a magnetic field is if you have ever attached a note to a refrigerator door with a small magnet or accidentally erased a credit card by moving it near a magnet. The magnet acts on the door or credit card via its magnetic field.
The applications of magnetic fields and magnetic forces are countless and changing rapidly ...