Biomedical Applications of Avalanche Semiconductor Detectors

The attractiveness of silicon avalanche radiation detection systems lies in the following properties: (1) Extremely low noise and low background counting capability, which is maintained to temperatures as high as 100°C, without resorting to coincidence techniques. (2) Sensitivity to virtually the entire range of nuclear radiations and energies with highest efficiency concentrated in the low energy or soft radiation region without requirement for cooling. (3) Ruggedness and miniaturizeability-a characteristic shared with other semiconductor detectors--but, in addition, providing a larger degree of usefulness in extra-laboratory applications due, primarily, to the high signal level from the detector. These characteristics make avalanche systems potentially quite valuable in nuclear medicine, particularly for in vivo detection of lower energy radiations. This paper will describe a program that was undertaken to fabricate ten prototype avalanche detector instruments for collaborative research purposes with investigators in the fields of nuclear medicine and radiobiology. All ten instruments are currently in the hands of such researchers. The specific areas of investigation are varied and interesting, with a number being rather exciting from the standpoint of being new accomplishments, i.e., avalanche technology appears to be making possible some measurements and procedures not considered feasible heretofore. Examples of specific applications being investigated are transmission bone scanning, tumor detection and diagnosis (opthalmic and skin types), organ scanning by x-ray fluorescence techniques, tooth enamel density measurements and soil water content and pressure determinations. Some very preliminary results are available on several of the above studies.