Nuclear energy on Earth

Nuclear processes can release a million times the energy of a chemical process. For this reason, mankind has tried to make use of this energy source for both military purposes and for power production. Both purposes involve very significant issues of public policy. Exploring these issues would take us too far from study of stars, but we should at least take advantage of what we have learned so far so as to understand the basic facts.

There are two kinds of ways that nuclear energy has been used: fission and fusion.

Fission

Fission involves very heavy nuclei. The big nucleus absorbs a neutron and breaks up, releasing more neutrons.

The most important reactions are

²³⁵U + n --> two smaller nuclei + more n's
- naturally occuring uranium is mostly ²³⁸U
- ²³⁵U is separated from the ²³⁸U with a difficult process.
²³⁹Pu + n --> two smaller nuclei + more n's
- ²³⁹Pu does not occur naturally it can be made in reactors
²³³U + n --> two smaller nuclei + more n's
- ²³³U does not occur naturally it can be made in reactors

Each of these reactions release about 200 MeV of energy.

These reactions are used for bombs.

The first reaction is most commonly used for commercial power generation.

Fusion

To make use of fusion, one does not want to use the cycle in the Sun because its first step is too slow. Instead one burns H to make He, but starting with ²H or ³H.

An example is ²H + ³H --> ⁴He + n.

This releases 18 MeV of energy.

Recall that the hydrogen nuclei will repel each other because of their electric charge. Thus the hydrogen must be very hot in order for them to get near enough to each other for the strong interactions to be effective and make the reaction occur. This and similar reactions are used to make hydrogen bombs. The hydrogen is heated with a fission bomb.

There is a big effort underway to make this work for commercial power generation. The difficult trick is to get the hydrogen hot and dense enough. The main approach being tried is to make a plasma that is hotter than the middle of the Sun, although not as dense. The plasma is to be confined a strong magnetic field.

Cold Fusion

In 1989 an amazing discovery was announced by two chemists working at the University of Utah: they could make nuclear fusion work at room teperature instead of millions of K. The reactions involved deuterium (²H).

It was known that deuterium could undergo the fusion reactions

²H + ²H --> ³He + n. (3 MeV)
²H + ²H --> ³H + p. (4 MeV)

When two deuterons collide, the first reaction occurs about half the time, the second about half the time.

The chemists held the deuterium is palladium rods, making use of the fact that palladium likes to absorb hydrogen.

They reported that more energy was produced in their apparatus than was used to force the deuterium into the rod. They attributed the excess energy to nuclear fusion.

If this were true it would imply

a very fundamental discovery in physics had been made:
- the distances between deuterium nuclei in the palladium is approximately 10^-10 m.
- the distance between the deuterium nuclei in order for fusion to happen needs to be 10^-15 m.
- the deuterium nuclei repel each other.
this discovery would have enormous economic consequences.

Further experiments by many groups were not able to confirm the reported result.

By 2007, this "news" has pretty much died down, but it was still continuing in 1996. For instance, there was a news story on Eugene television in 1996 about the ``Patterson cell'' for energy production. Here is a (rather cynical) report on it from an electronic newsletter, WHAT'S NEW by Robert L. Park, Friday, 9 Feb 96, Washington, DC:

3. ALTERNATIVE ENERGY: READY FOR A REMAKE OF PONS & FLEISCHMANN? An ABC News story this week followed a familiar script: credulous reporter interviews smiling man in white smock, who explains that when he coats tiny beads with copper, nickel and palladium, puts them in salt water, and then runs a current through the mess, he gets 100 times more energy out than he puts in. Reporter touches cell and exclaims, "It's warm!" How does it work? Inventor says he has no idea. Reporter puts on his serious face and looks into the camera: "There have been dozens of claims of ideal energy sources, but this device is different. It has attracted serious interest from major companies and been verified by scientists at prestigious universities." Now insert a seven-second sound bite from a skeptic for "balance," and then one final shot of the inventor, James Patterson, writing science stuff on a blackboard.

ASTR 122 course home page

Updated 10 October 2007

Davison E. Soper, Institute of Theoretical Science, University of Oregon, Eugene OR 97403 USA