How are elements born?

A number of reactions take place in the sun that cannot be duplicated on Earth. Some of these reactions involve the formation of large elements from smaller ones. So far, we have only been able to observe formation of very small elements here on Earth. The reaction sequence observed appears to be the following: Hydrogen-1 atoms collide to form the larger hydrogen isotopes, hydrogen-2 (deuterium) and hydrogen-3 (tritium). In the process, positrons and gamma rays are formed. The positrons will collide with any available electrons and annihilate, producing more gamma rays. In the process, tremendous amounts of energy are produced to keep us warm and continue supplying reactions.

Nuclear Fusion

Figure 1. Nuclear fusion reaction between deuterium and tritium.

In contrast to nuclear fission, which results in smaller isotopes being formed from larger ones, the goal of nuclear fusion is to produce larger materials from the collision of smaller atoms. The forcing of the smaller atoms together results in tighter packing and the release of energy. As seen in Figure 1, energy is released in the formation of the larger atom, helium (He)  from the fusion of hydrogen-2 and hydrogen-3 as well as from the expulsion of a neutron.

This release of energy is what drives research on fusion reactors today. If such a reaction could be accomplished efficiently on Earth, it could provide a clean source of nuclear energy. Unlike fission reactions, nuclear fusion does not produce radioactive products that represent hazards to living systems.

Nuclear fusion reactions in the laboratory have been extraordinarily difficult to achieve. Extremely high temperatures (in the millions of degrees) are required. Methods must be developed to force the atoms together and hold them together long enough to react. The neutrons released during the fusion reactions can interact with atoms in the reactor and convert them to radioactive materials. There has been some success in the field of nuclear fusion reactions, but the journey to feasible fusion power is still a long and uncertain one.

Summary

• The process of nuclear fusion is described.
• Examples of nuclear fusion reactions are given.

Practice

Read the material at the ling below and answer the following questions:

http://science.howstuffworks.com/fusion-reactor.htm

1. What temperatures are needed for fusion to occur?
2. Why is high pressure needed?
3. What does a magnetic confinement reactor do?
4. How does an inertial confinement method work?

Review

1. What is nuclear fusion?
2. Why is nuclear fusion of interest today?
3. What is one problem with studying nuclear fusion in the laboratory?

Glossary