Mike Van Voorhis age 11, of Tekoa, Washington, for his question:

How is plutonium made?

The first few atoms of plutonium promised that the large scale use of atomic energy is possible. This was in the 1940s, when nuclear physicists were striving to create the A bomb, hoping that it would make future warfare unthinkable. However, plutonium also proved that enormous nuclear energies can be tamed and used for peaceable purposes.

The Atomic Age was born in the first half of the 20th century and history may rate plutonium as its key radioactive element. We call it a man made element, though a few atoms occur in nature during the radioactive decay of natural uranium. Small traces are found in uranium ores. But large amounts of plutonium actually create themselves within a nuclear reactor.

We can claim that the nuclear reactor that makes this possible is man made, though it merely concentrates and controls the radioactive processes of nature. This nuclear fission, or atom splitting, works in stages with the help of isotopes. These are different forms of atoms of the same element. The atomic number or uranium is 92 because the nuclei of all its atoms have 92 positive charges, or protons. But their masses may vary because some have unusual numbers of neutral particles. These isotopes have different properties. For example, U 235 is a highly radioactive nuclear fuel, but this isotope makes up only a very small fraction of natural uranium. About 93 per cent of the mixture is U 238    and this isotope is not a useable nuclear fuel.

Separating the isotopes is tedious and very costly. However, plutonium made this unnecessary. Inside the shielded reactor, where the activity is intense and concentrated, fast acting U 235 emits high speed particles that crash through crowded atoms. Nuclei are split and their scattered particles shatter other nuclei, starting the chain reaction of nuclear fission.

Here and there, a high speed proton is absorbed by an atom of stodgy U 238. The extra weight changes it to isotope U 239    and also upsets its nucleus. To restore some of its balance, it emits a negative beta particle from a neutron. The neutron becomes a proton and the extra proton changes the atom to element 93    which is neptunium. But not for long. Another beta particle is emitted, creating an element with 94 positive charges. This is plutonium    and radioactive plutonium has the same fission fuel qualities as the uranium isotope U 235.

Hence, plutonium creates itself when U 238 is bombarded with carefully controlled neutrons inside a nuclear reactor. The starter fuel may be trigger happy U 235. But its fast flying bullets start a chain reaction of nuclear fission. This converts the U 238 into neptunium, which converts itself into plutonium. As the original fuel is consumed, more fissionable plutonium is stockpiled to feed the nuclear fission reactors of the future.