The first thought that people usually have when the subject of the usefulness of particle accelerators comes up in conversation is that they are really only used in the field of nuclear particle research. Few people realize that there are some very practical commonplace applications of nuclear particle accelerators.
Perhaps the most important of these is in the field of medicine. The National Cancer Institute reports that the five-year survival rate for all cancers in the early 1950’s was only 35 percent. Developments in radiation treatments increased that survival rate by the year 2000 to 59 percent. With early detection and treatment the five-year survival rate is now 80 percent. Some hospitals have their own nuclear medical facilities for the production of heavy charged particles. These are used to bombard and destroy cancerous tumors. Protons are preferred because they can be targeted precisely as a fine beam with no residual radiation. Proton production is achieved by one method using a linear accelerator (linac) injection system and a compact synchrotron with subsequent delivery of the heavy ions to treatment areas. Research in the treatment of different types of tumors using different types of nuclear particles such as Pi mesons and neutrons which are also produced by accelerators is currently being undertaken with varying degrees of success. Accelerators can be found at every major medical center in the Western world. This has led to the creation of new career types such as medical physicist and radiation oncologist.
Biomedical researchers have learned to harvest synchrotron radiation, which occurs when charged particles are accelerated in a curved path or orbit as in the synchrotron which is a circular particle accelerator, and channel it into a beam in order to examine the positions of the atoms in a protein molecule. The beam passes through a protein crystal and is scattered onto a detector. Researchers are able to view a 3D image of the protein using computers which analyze the scattering pattern.
Neutron beams produced by accelerators are used to study the nuclei of condensed atoms. A Bose Einstein condensate is a collection of atoms which has been supercooled to a few fractions of a degree above absolute zero. They are in what is termed the ground state and they behave collectively as essentially one large atom. Neutrons do not have an electromagnetic charge which would affect this ‘super atom’ and at the low temperature of the condensate the wavelength of the beam is made to closely match that of the condensate. The result of accelerating the neutrons increases their momentum and this reduces their wavelength sufficiently to make this possible. This is considered the best way to at least partially defeat Heisenberg’s uncertainty principle which states in effect that certain determinations cannot be made of a particle under observation because the particle is affected by the means used to measure those determinations.
Neutron scattering can actually be used to study the nuclei of atoms. Researchers are now are able to characterize the hydrogen bonds of many materials. Neutron diffraction is the only method by which the magnetic order and the magnetic excitations of many materials can be established.
Production of radioactive isotopes used in diagnostic imaging systems is achieved by bombarding tight proton beams produced by accelerators at specially designed targets. Some examples of these isotopes are strontium-82, which yields rubidium-82, used for Positron Emission Tomography (PET) scans of the heart; copper-67, used for cancer detection; and germanium-68 which is used to calibrate PET scanners. Targeting cobalt with Neutron beams results in production of the radioactive isotope cobalt-60 which is used to treat cancer and for sterilizing objects. These are just a few of the many uses of the numerous radioactive isotopes produced by particle accelerators in all fields including not just medicine but also agriculture and industry. Outlining all of their many applications is simply beyond the scope of this article.
Particle accelerator research has produced some important spin-offs. Research into the containment of antiprotons now regularly produced by large accelerators like the one at the European Institute for Nuclear Research (CERN) has led to the development of the Penning Trap by researchers at Penn State University. This is a portable antiproton storage device. A byproduct of the Penning Trap is the isotope O-15 which is used in PET scans of the human brain. Since few hospitals have the facilities to produce this very valuable isotope the Penning Trap will make possible the delivery of O-15 to any institution which requires it.
Magnetic Resonance Imaging (MRI) systems use a technology that was originally designed to accelerate protons to the highest energy levels possible. The superconducting wire and cables used by MRI’s were first developed in the 1970’s to build the Tevitron accelerator at Fermilab.
The future of particle accelerators may lie in power generation. Bombarding thorium nuclei with neutrons transforms thorium-232 into uranium-233 which collides with more neutrons and splits in two, releasing a lot of energy and yielding yet more neutrons in the process. A continuous cycle which requires supplying neutrons to keep the process of fission ongoing produces no nuclear waste. While still highly theoretical, such a power generator could be built using existing technologies.
Particle accelerators are evidently very useful. The contributions they have made have enriched our lives more than most of us know. Our desire to know more about the structure of matter has truly been rewarding.
