Of great importance are those experiments that determine the probability of producing each of the three types of mesons in a nuclear collision. This type of experiment is repeated for different beam energies and target elements. Other experiments measure the energy and direction of emission of π mesons from a target.
A typical π-meson experiment is represented in Fig. 9. The purpose of this experiment was to detect the spin directions of protons as they are knocked out of a liquid hydrogen target by a π-meson beam. (Like the earth, a proton spins on its axis.) An extracted proton beam from the cyclotron enters the physics cave from the left, striking a polyethylene target and producing π mesons. A beam of these mesons is formed by a series of two bending magnets and three focusing magnets. This beam passes through a carbon absorber to remove unwanted particles. The meson beam then strikes the liquid hydrogen target. A few of the incoming mesons scatter, knocking protons out of the liquid hydrogen. Scintillation counters at A and B record the passage of a proton, thus defining its direction. The scattered mesons are counted by a scintillation counter at C. A few of the protons scatter off the carbon target and are detected by counters at E and D. From the detection of such events, the spin directions (polarization) of the recoil protons can be analyzed. In this way, more is learned about the fundamental π-proton interaction.
Further studies of the interactions of π mesons are made in the meson cave. Other experiments performed there are concerned with μ mesons. The μ meson (muon) is a particle created in the decay of a π meson and is the principal constituent of cosmic rays striking the surface of the earth. The muon is unstable, eventually undergoing a radioactive decay into an electron. Although the muon does not experience nuclear forces, it can interact weakly with nuclei. The behavior of the muon is well understood, but its role as one of the elementary particles is unknown. That is, if the muon did not exist, what effect would this have on the structure of matter? The answer to this question, among others, is being sought by physicists using the 184-inch cyclotron.
Biophysics
Experiments in biophysics are conducted in the medical cave. In these the interest lies not in nuclear interactions but in the effect of ionizing radiation on living tissue. High-energy beams of particles can be used for selective destruction of specific areas of the brain. This permits physiological mapping of the functions of the brain in experimental animals. It further offers a therapeutic approach to the treatment of brain tumors. One of the important investigational programs is concerned with the relationship of the pituitary gland to the growth rate of certain cancers and to some endocrine disorders.
Nuclear Chemistry
For techniques of radiochemistry to be employed successfully, high interaction rates (and therefore high beam intensities) are needed. For this reason, chemistry targets are usually inserted right into the cyclotron so that they can be bombarded directly by the circulating beam. After the bombardment is completed the target is removed from the cyclotron. It is then taken to a chemistry laboratory and subjected to detailed chemical procedures. Individual elements are removed, and the radioactive isotopes of each element are identified by quantitative counting techniques. In some cases a mass spectrometer is used to analyze the products. Many deductions about the nature of the breakup of the target nucleus can be drawn from the pattern of the observed radioactive products. Sometimes the nucleus splits almost in half. This is called fission. More frequently smaller parts of the nucleus are split off. Two general types of reactions, known as spallation and fragmentation, are distinguished. One of the goals of this research is to learn more about the constitution of the nucleus and of the forces which bind the particles in the interior of the nucleus.