Neutron

The atom's structure has a nucleus at the center, surrounded by a cloud of electrons. Inside the nucleus are two types of particles, neutrons (electrically neutral) and protons (positively charged). Under special experimental conditions, neutrons can be released from the nucleus. They are useful for creating new radioactive materials or for producing large amounts of nuclear energy .

The atom is so small that it would take several million of them to equal the size of the period at the end of this sentence. The nucleus is much smaller still, about 1/100,000 of an atom's size. Finally, neutrons and protons appear to be made up of three even smaller components called "quarks." Evidence for quarks comes from experiments done with very high energy particle accelerators .

Discovery

The neutron as a distinct, separate particle was discovered in l932 by a British physicist, James Chadwick (1891-1974). He was using radiation emitted from radioactive radium to bombard various materials. When he irradiated the element beryllium, he found that a very penetrating particle was produced. It could go through an inch thickness of lead . Chadwick reasoned that the new particle must be electrically neutral, because all other radiation known at that time would have been stopped by the lead. Chadwick was awarded the 1935 Nobel Prize in physics for his discovery.

New radioactive materials

Enrico Fermi (1901-1954), a young Italian scientist, constructed a neutron source according to Chadwick's design, mixing radium and beryllium powder together in a small glass tube. Fermi's plan was to use this neutron source for making new radioactive materials. Together with his co-workers, he was successful in producing radioactive sodium , iron , copper , gold, and many other elements. Fermi received the l938 Nobel Prize in physics for his work with neutrons.

Almost all elements found in nature can now be made radioactive. Radioactive potassium and phosphorus are used as tracers to measure how effectively plants take up fertilizer from soil . Radioactive iodine is applied in nuclear medicine to diagnose and treat thyroid problems. Radiation treatment for cancer therapy uses radioactive cobalt, which is made by irradiating ordinary cobalt with neutrons.

Nuclear energy production

When the element uranium is bombarded by neutrons, a unique reaction called fission takes place. The uranium nucleus breaks into two pieces, which fly apart with a large release of energy. In addition, several extra neutrons are emitted. These cause more uranium nuclei to split apart, which creates more energy and more neutrons in a so-called "chain reaction" process. In an atomic bomb, the chain reaction becomes an uncontrolled explosion. In a nuclear power plant, the chain reaction is maintained in a steady state by control rods which absorb extra neutrons.