© 2010 Pearson Education, Inc. Lecture Outline Chapter 30 College Physics, 7 th Edition Wilson / Buffa / Lou

30.1 Nuclear Reactions In nuclear reactions, one pair of nuclei becomes a pair of different nuclei. Example: Or, more accurately, The intermediate state is usually omitted from the equation. © 2010 Pearson Education, Inc.

30.1 Nuclear Reactions Energy is always conserved in nuclear reactions, although it is necessary to take mass energy into account. The Q value is the change in kinetic energy from the initial nuclei to the final ones. In the reaction If Q is positive, the reaction may proceed spontaneously; if Q is negative, energy must be added before the reaction can occur. © 2010 Pearson Education, Inc.

30.1 Nuclear Reactions © 2010 Pearson Education, Inc.

30.2 Nuclear Fission In a fission reaction, a heavy nucleus splits into two lighter nuclei. Fission may be either spontaneous or induced. Example: This is induced fission; the incoming neutron excites the uranium nucleus into fissioning. © 2010 Pearson Education, Inc.

30.2 Nuclear Fission Fission is reasonably well described by the liquid-drop model, which models the nucleus as an oscillating liquid drop that eventually splits. © 2010 Pearson Education, Inc.

30.2 Nuclear Fission The daughter nuclei from fission are not unique; many different decay modes are possible. Examples: Note that in each case there are more outgoing neutrons than incoming ones. © 2010 Pearson Education, Inc.

30.2 Nuclear Fission If the outgoing neutrons have the correct energy to induce further fission, a chain reaction can take place. There is a minimum mass required, called the critical mass, in order to sustain a chain reaction. © 2010 Pearson Education, Inc.

30.2 Nuclear Fission If the chain reaction is uncontrolled, an enormous explosion takes place. This is the operating principle behind nuclear weapons. Controlling the chain reaction allows the production of energy; if the reaction can be sustained indefinitely, commercial power generation is possible. © 2010 Pearson Education, Inc.

30.2 Nuclear Fission A nuclear reactor contains a complex set of fuel rods, control rods, and moderator. The control rods (which absorb neutrons) are movable; they are positioned so that the chain reaction is stable. A considerable amount of heat is produced, so the rods are usually submerged in flowing water, called cooling water. If the control rods are completely inserted, the chain reaction stops. The water also acts as a moderator, slowing the neutrons so they are more likely to induce fission. © 2010 Pearson Education, Inc.

30.2 Nuclear Fission This diagram illustrates how the heat created in the reactor vessel is used to generate electricity. © 2010 Pearson Education, Inc.

30.2 Nuclear Fission If the flow of coolant stops, the reactor can become very hot and even melt. This could lead to the release of some radioactive material. The accidents at Three Mile Island and Chernobyl were of this type, although the Chernobyl accident was complicated by a poor design that allowed the chain reaction to go out of control. © 2010 Pearson Education, Inc.

30.3 Nuclear Fusion Energy can be produced through the fusion of very light elements. Example, deuterium–tritium fusion: © 2010 Pearson Education, Inc.

30.5 Fundamental Forces and Exchange Particles Looking at the fundamental interactions between elementary particles, we find there are four: Gravitational force Electromagnetic force Strong nuclear force Weak nuclear force © 2010 Pearson Education, Inc.

30.5 Fundamental Forces and Exchange Particles Attempts to create a successful quantum theory of gravity have so far been unsuccessful, as have attempts to detect the graviton. This table summarizes the four forces. © 2010 Pearson Education, Inc.