Quick Facts: Indiana University Cyclotron Facility

Quick Facts

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An atom is the basic building block of all matter; it is the smallest particle of an element that still exhibits the characteristics of that element. Atoms consist of a positively-charged nucleus containing protons and neutrons, surrounded by negatively charged electrons which move in orbits around the nucleus.

Begin with ordinary table salt.
Enlarge it 10,000,000 times and you will find the crystal structure of salt, composed of atoms of sodium and chlorine. Like salt, all substances are made of atoms.
Enlarge it again 10 times and you will find the structure of individual atoms. An atom of sodium contains 11 electrons and a very tiny nucleus.
Enlarge the nucleus 10,000 times and you will find it is made of particles called protons and neutrons. The sodium nucleus has 11 protons and 12 neutrons. The protons and neutrons hold themselves together by exchanging mesons, lighter particles that live only a short time.
Enlarge the nucleus another 10 times and the structure of individual protons and neutrons appears. Each one contains three permanently confined particles called quarks. The quarks hold themselves together by exchanging gluons. The force generated by the gluons is so strong that no quark has even been observed separated from its original proton or neutron.
The nucleus cannot be viewed directly. The nucleus and its properties may be known only through the particles or radiation created in nuclear reactions. In the laboratory, nuclear reactions are generated by the collision of two nuclei at high speed. (This process is repeated in nature within the interior of stars and in interstellar space.)

Protons, neutrons and electrons are the particles that make up an atom.

Protons are found in the nucleus and have a positive electrical charge equal to the negative charge of an electron and a mass similar to that of a neutron. The number of protons that an atom has determines which chemical element it becomes, e.g., sodium has 11 protons, hydrogen has 1 proton.
Neutrons have zero charge, unlike protons, which are positively charged. A neutron has slightly more mass than a proton, and about 1800 times more mass than negatively-charged electrons.
Electrons are negatively charged particles commonly found in the outer layers of atoms. The electron has only 0.0005 times the mass of the proton.
The charge and relatively large mass (~1800 times that of an electron) of protons account for the Bragg peak, an effect in which the proton, as it slows down going through matter, leaves most of its energy very close to the point where it stops. It is this effect that makes proton radiotherapy an effective clinical tool.

Quark

The quark is a fundamental particle and one of the basic building blocks of matter. Quarks are bound together by exchanging gluons to make the protons and neutrons that make up the nuclei of atoms. There are thought to be 6 types of quark: up and down, top, bottom, strange and charm quarks. A proton consists of two up quarks and one down quark. A neutron consists of two down quarks and one up quark. No quark has yet been observed in isolation.

Gluon

Neutrinos

The "little neutral one" is a small particle that has no charge and is thought to have very little mass. Neutrinos are created in energetic collisions between particles and are thought to exist in massive numbers throughout the universe. The nature of the neutrino is not fully understood as they interact very weakly and can be observed only rarely. Understanding the neutrino is important in determining the structure and evolution of the universe.

There is an ION SOURCE where protons are removed from hydrogen atoms.
There is an ACCELERATOR where these protons are given enough speed to penetrate to the nuclei of beryllium and knock neutrons out of the nucleus. These high speed protons are referred to as a beam.
The MODERATOR contains the beryllium metal target, which is located at the center. The neutrons that come out of the beryllium quickly go into other materials that surround the target. Here they collide with other nuclei. But instead of making nuclear reactions, they merely slow down with each collision. Eventually they have only 1 part per billion of their original energy. For each beam line, holes in the moderator material allow these slow (low energy) neutrons to escape.
Each neutron is associated with a quantum mechanical wave. Because the neutrons are traveling so slowly, the length of this wave gets bigger by about a factor of 100,000 so that it is about the size of an atom or a molecule. The interaction of this wave with various materials allows researchers to study the properties of the material. So along each line there is an INSTRUMENT that measures the effect of the material on the neutron’s wave by looking at the way that it scatters. From this information, researchers can learn about the arrangement of atoms, the sizes and shapes of molecules (such as proteins), and the properties of surfaces. One can even use the neutrons to form a radiographic image of the inside of the material.