of complex data samples and to allow comparison between various theoretical models and experimental results.

Experimenters have often made great advances when they have been able to borrow a technology developed for other uses and modify it to allow advances in particle physics. Similarly, a technology has often been developed specifically to address the needs of the elementary-particle physics community but then has been adapted to meet the needs of society outside particle physics. Although it is often evident where the technical barriers in elementary-particle physics (EPP) reside, it is much more difficult to predict where the breakthroughs will be and how they will come about. Experience has shown, however, that innovative new technologies or innovative uses for existing technologies will find surprising applications beyond those originally conceived by the developers.

THE MACHINE FRONTIER

The development of particle accelerators has led to new tools for basic research, medicine, and industry. Synchrotron radiation, the bane of elementary-particle physicists in their quest for ever-higher energy electron accelerators, is now used in cutting-edge research in the materials sciences and in studies of biological systems. Accelerator-generated proton beams produce pulses of neutrons when they strike high-atomic-weight targets; these neutron sources play an important role in understanding the chemistry and physics of materials. Low-energy proton and pion beams, having served the needs of the elementary-particle physics community 40 years ago, are now used routinely in medical diagnostics and therapy. Cyclotrons, whose technology was first developed in the 1930s, now find medical application in the production of isotopes used for positron emission tomography (PET).

Industry employs particle beams for ion implantation in semiconductor devices, sterilization of materials, and x-ray lithography via synchrotron radiation. Using intense proton beams impinging on a target to produce neutrons can be a safer alternative to nuclear reactors. Proposed applications include the production of tritium, the destruction of plutonium and other high-level radioactive waste from nuclear weapons production and nuclear power plants, and even energy production by initiating fission in a subcritical reactor. National security is strengthened by current research into accelerator sources for explosives and contraband detection, neutron and proton radiography, and weapons effects simulations.

SYNCHROTRON RADIATION: USING X-RAY LIGHT TO SEE THE WORLD IN ATOMIC DETAIL

As described in Chapter 6, electrons, when forced to travel in circles, lose energy through the mechanism known as synchrotron radiation. For electron



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