The planning of scientific field experiments that use delicate optical instrumentation poses a challenge to the designer. At the U.S. atomic test site in Nevada, many experiments are conducted under the most adverse conditions for instrumentation, including extremes of temperature and dust, while the instruments are being installed, aligned, and tested above ground. They are subjected to mechanical shock while being lowered into place deep underground and during the back-filling process. Before being destroyed by the blast, they then must operate in intense radiation fields long enough to transmit their data to a recording station. In this paper we present the design and implementation of the "downhole" portion of a measuring system for gamma rays. Included are three alternative designs for radiation-resistant collimating and condensing lenses, sample cells, turning mirrors, and fiber-optic termination techniques. Also discussed are mechan-ical mounts and positioners, shielding, alignment, test methods, and field installation. Some general design suggestions for optical systems in adverse environments are also presented.
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