05 Nuclear and Elementary Particle Physics

The acceptance, only a bit more than 100 years ago, that ordinary matter is composed of atoms and then the discovery that these atoms have an internal structure, have opened up the deepest aspects of the universe to our investigation. Or are these the deepest aspects? In fact, some phenomena associated with nuclear and subnuclear structure and behavior are part of our daily experience, principally through exposure to natural radiation of both terrestrial and cosmic origin. What instrumentation gives use a clearer and quantitative understanding of this radiation and its interaction with matter, including our own bodies? What does the apparent randomness of the "clicks" of particles detected by a Geiger counter tell us about fundamental probabilistic aspects of nature? How has the further discovery of short-wavelength electromagnetic radiation - namely X-rays and gamma-rays - both elucidated atomic and nuclear structure and given us new probes for investigating matter? When particles like electrons, protons, neutrons, or helium nuclei are given high energy, what is the nature of their interaction with each other and with matter in general? What doorways does the study of collisions of these particles open to find, deeper still, a whole new realm of subatomic particles and how have subsequent discoveries given rise to an extraordinary view of the ultimate character of matter and energy called the "Standard Model"? Is this model complete or even, ultimately, the actual truth of existence?

Image source: Muon Decay.png: Thymo / derivative work: Sgbeer, Public domain, via Wikimedia Commons