An alphabetical list of sites follows this outline.




Atomic properties It is important, though not easy, to have a picture of matter at the atomic and subatomic level, and an understanding of the properties of atoms. An atom is too small to see with the naked eye or with a normal microscope. 10-8 centimeters is a typical atomic size, meaning that 108 atoms lined up would stretch to one centimeter.

The constituents of the atom are electrons, protons and neutrons. Protons and neutrons are bound together (by a nuclear force) in the core or "nucleus" of the atom. Electrons occupy a much larger volume outside the nucleus, but most of the mass of the atom is in the nucleus. One can think of a small dense core, surrounded by a tenuous outer cloud of electrons. The interactions between the electron clouds of different atoms are responsible for chemical reactions, and most phenomena we observe in everyday life. However, it is the interactions of nuclei that we will be concerned with in this part of this course.


Nuclear properties
In atoms the number of electrons equals the number of protons. This number is called the atomic number (symbol, Z). Atoms with a given atomic number make up a particular chemical element. The Element Tables list the chemical elements in order of atomic number, and also in alphabetical order.

For example, Z=1 is hydrogen, Z=8 is oxygen, Z=26 is iron. The number of neutrons (symbol, N) is in some cases equal to or close to Z, but not always. The properties of nuclei are determined entirely by Z and N. Nuclei with the same Z and different N are called isotopes. The Nuclear Table gives an overview of various nuclei that will be important in our work.


Radioactivity
Radioactivity was first studied by Becquerel, Rutherford, and Curie in the early twentieth century. It is a process in which an unstable nucleus emits a small particle and is transformed into a different nucleus. There are three types of radioactivity, labelled "alpha", "beta", and "gamma". Problem Set 4 is based on the radioactivity site. An additional site provides a brief discussion of medical effects on humans.

In the radioactivity experiment that we will do at the end of the term, we will measure the half-life of a radioactive nucleus.


Nuclear reactions
A nuclear reaction occurs when two nuclei collide, and each is changed in some way. Problem Set 5 is based on the nuclear reaction site.


Nuclear fission
Fission is a process in which an unstable nucleus breaks into two pieces (typically medium-sized nuclei). Usually these products are accompanied by free neutrons. The presence of these neutrons creates the possibility of a chain reaction, and an explosive release of energy. This is the principle of the atomic bomb. Two materials, uranium-235 and plutonium, have been used to build fission explosives. Problem Set 6 is based on the fission site.


Reactors
In a nuclear reactor fission is controlled. Energy is released continuously, and can be used to generate electricity. Although a significant amount of electricity is produced worldwide by reactors, development has slowed in western countries, partly because of fear of nuclear accidents, and because of concern about the disposal of nuclear waste. On the other hand, nuclear generation does not produce the kind of greenhouse gases that lead to global warming, and so may become a necessary alternative to fossil fuels (oil, coal, natural gas).

Today scientists and engineers are studying various alternatives to the current reactor design, including the heavy-metal reactor, which can utilize the energy in 238U, and may help solve the problem of nuclear waste.

Fusion
Fusion is an alternative method of generating energy via nuclear processes. Small nuclei (isotopes of hydrogen and helium) fuse to form larger nuclei. Practical application of fusion for generating electricity lies several decades in the future.

Fusion research aims at imitating the source of the sun's energy.


Nuclear weapons
Most nuclear weapons today make use of fusion reactions.

Energy and mass
In fission and fusion reactions, as well as in radioactivity, the nuclei produced by the process have less total mass than the nuclei that initiate the process. This lost mass is converted to energy in accordance with Einstein's theory of relativity,
E = mc2.


The nuclear arms race
Explosive fusion (triggered by a fission bomb) is the mechanism in the thousands of nuclear weapons in the world today. The capability of building these weapons, and making them deliverable by airplane and by missile, led to the nuclear arms race between the Soviet Union and the United States. With the demise of the Soviet Union and the end of the Cold War in 1989, weapon deployment began to be reduced, and planned reductions continue through 2012. But the nuclear arsenal will continue to play a part in U.S. military strategy.


Open questions
Additional issues remaining on the agenda include:
  • limiting or stopping the proliferation of nuclear weapons to other nations,
  • deciding whether a defensive system can (and should) be built to protect the U.S. from enemy missiles,
  • considering a proposed ban on nuclear testing,
  • defending the U.S. against nuclear terrorism.

THE FOLLOWING SITES ARE REQUIRED:

SITES FOR CHOICE
Choose five of the following sites:

The site on Marie Curie is maintained by the American Physical Society, and based on a recent biography. All of the information is interesting, but if you choose this site you are responsible only for the two sections entitled "X-rays and Uranium Rays" and "The Discovery of Polonium and Radium".

The site on nuclear terrorism is maintained by the Center for Defense Information, and written by Bruce Blair, a leading expert on nuclear weapons.

SITES FOR REFERENCE