Silicon detectors are also limited in their resistance to radiation. These detectors must be carefully designed and the background environment accurately modeled to ensure many years of efficient operations at facilities such as the Tevatron collider or the LHC.

Typically, two avenues may be pursued to mitigate such effects. On the one hand, the materials used can be improved, which is the current situation with respect to silicon devices. Research is being conducted to modify those characteristics of the material that make it sensitive to radiation. As with the original development of silicon detectors, this requires cooperation between the user and the manufacturer. Often the problem involves impurities in the material at the level of parts per million or less. At this level, few manufacturing processes are understood. Furthermore, the materials science of the detector is not entirely understood. The particle physicist then has to grapple with issues of solid-state physics.

The alternative path is to look for new materials. There was hope for a few years that the use of gallium arsenide instead of silicon would be a solution. In terms of neutron damage, gallium arsenide held promise. However, measurements were then made with charged particles, pions, and protons, and gallium arsenide was found to be less resistant than silicon. A possibility currently under investigation is the use of commercial diamond crystals. This also looks promising, but considerable development is required before a viable and affordable solution can be identified.

Opening New Possibilities

Significant R&D efforts are aimed at developing the detector technologies that will be required to support future experimentation at electron, proton, and/or muon facilities. This section has described a few areas in which the needs for future development are accompanied by a sense of the directions that are most fruitfully pursued. However, it should be emphasized that progress is required on a wide range of fronts and breakthroughs can occur any time a physicist is presented with some new possibility, perhaps developed outside the confines of elementary-particle physics, that acts as a stimulus. Research and development of detectors with no apparent immediate application has always been, and will continue to be, a necessary component of particle physics research.

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