Quantum Physics

This photo shows scientist MelissaDouglas and part of the Z machine,an inertial-electrostatic confinementfusion apparatus at Sandia NationalLaboratories. In the device, giantcapacitors discharge through a gridof tungsten wires finer than humanhairs, vaporizing them. The tungstenions implode inward at a million milesan hour. Braking strongly in the gripof a “Z-pinch,” they emit powerfulx-rays that compress a deuteriumpellet, causing collisions between thedeuterium atoms that lead to fusionevents.Nuclear Energy andElementary ParticlesIn this concluding chapter we discuss the two means by which energy can be derived fromnuclear reactions: fission, in which a nucleus of large mass number splits into two smallernuclei, and fusion, in which two light nuclei fuse to form a heavier nucleus. In either case,there is a release of large amounts of energy, which can be used destructively through bombsor constructively through the production of electric power. We end our study of physics byexamining the known subatomic particles and the fundamental interactions that govern theirbehavior. We also discuss the current theory of elementary particles, which states that all matterin nature is constructed from only two families of particles: quarks and leptons. Finally, wedescribe how such models help us understand the evolution of the Universe.30.1 NUCLEAR FISSIONNuclear fission occurs when a heavy nucleus, such as 235 U, splits, or fissions, intotwo smaller nuclei. In such a reaction, the total mass of the products is less thanthe original mass of the heavy nucleus.Nuclear fission was first observed in 1939 by Otto Hahn and Fritz Strassman, followingsome basic studies by Fermi. After bombarding uranium (Z 92) with neutrons,Hahn and Strassman discovered two medium-mass elements, barium andlanthanum, among the reaction products. Shortly thereafter, Lise Meitner andOtto Frisch explained what had happened: the uranium nucleus had split into twonearly equal fragments after absorbing a neutron. This was of considerable interestto physicists attempting to understand the nucleus, but it was to have even morefar-reaching consequences. Measurements showed that about 200 MeV of energy isreleased in each fission event, and this fact was to affect the course of humanhistory.Sandia National Laboratories. Photo by Randy MontoyaCHAPTER30O U T L I N E30.1 Nuclear Fission30.2 Nuclear Reactors30.3 Nuclear Fusion30.4 Elementary Particles30.5 The Fundamental Forcesof Nature30.6 Positrons and OtherAntiparticles30.7 Mesons and the Beginningof Particle Physics30.8 Classification of Particles30.9 Conservation Laws30.10 Strange Particles andStrangeness30.11 The Eightfold Way30.12 Quarks30.13 Colored Quarks30.14 Electroweak Theoryand the Standard Model30.15 The Cosmic Connection30.16 Problems and Perspectives973