The Foundations of Chemistry

NUCLEAR FUSION

Fusion, the joining of light nuclei to form heavier nuclei, is favorable for the very light

atoms. In both fission and fusion, the energy liberated is equivalent to the loss of mass

that accompanies the reactions. Much greater amounts of energy per unit mass of reacting

atomsare produced in fusion than in fission.

Spectroscopic evidence indicates that the sun is a tremendous fusion reactor consisting

of 73% H, 26% He, and 1% other elements. Its major fusion reaction is thought to involve

the combination of a deuteron,^21 H, and a triton^31 H, at tremendously high temperatures

to form a helium nucleus and a neutron.

2

1 H

3

1 H88n

4

2 He

1

0 nenergy

Thus, solar energy is actually a form of fusion energy.

Fusion reactions are accompanied by even greater energy production per unit mass of

reacting atoms than are fission reactions. They can be initiated only by extremely high

temperatures, however. The fusion of^21 H and^31 H occurs at the lowest temperature of any

fusion reaction known, but even this is 40,000,000 K! Such temperatures exist in the sun

and other stars, but they are nearly impossible to achieve and contain on earth. Ther-

monuclearbombs (called fusion bombs or hydrogen bombs) of incredible energy have

been detonated in tests but, thankfully, never in war. In them the necessary activation

energy is supplied by the explosion of a fission bomb.

It is hoped that fusion reactions can be harnessed to generate energy for domestic

power. Because of the tremendously high temperatures required, no currently known

structural material can confine these reactions. At such high temperatures all molecules

dissociate and most atoms ionize, resulting in the formation of a new state of matter called

26-16

1032 CHAPTER 26: Nuclear Chemistry

The deuteron and triton are the nuclei
of two isotopes of hydrogen, called
deuterium and tritium. Deuterium
occurs naturally in water. When the
D 2 O is purified as “heavy water,” it
can be used for several types of
chemical analysis.

Our sun supplies energy to the earth

from a distance of 93,000,000 miles.

Like other stars, it is a giant nuclear

fusion reactor. Much of its energy

comes from the fusion of deuterium,

(^21) H, producing helium, (^42) He.
The explosion of a thermonuclear (hydrogen)
bomb releases tremendous amounts of energy. If
we could learn how to control this process, we
would have nearly limitless amounts of energy.