This photograph is of the world’s first observation of a neutrino in a hydrogen bubble chamber. The event was produced in a synchronized cyclotron on November 13, 1970. The invisible neutrino followed the dashed yellow line and struck a proton at the point from which the three particle tracks originate. The neutrino then turned into a muon, whose path is traced by the long blue line. The short red track, labeled “p,” follows the proton. The orange track marks the path of a pi-meson created by the collision. In this chapter, you will learn about the basic structure of the atomic nucleus.
Atoms of the same element always have the same number of protons in their nuclei, but they may have differing numbers of electrons or neutrons. Radioactivity is the result of nuclear decay and the emission of subatomic particles. Quarks are the smallest particles known to date; they are the building blocks of the primary subatomic particles. Nuclear reactors can release vast quantities of energy by harnessing the interactions of atomic nuclei.