not be discussed further. In an image dissector tube, electrons emitted from specific areas of the photocathode can be selectively focused on a dynode structure. As such, the image dissector can be viewed as an array of photomultipliers. Three features of the image dissector tube which could be attractive in some situations are its nonintegrating response, its high sensitivity (via internal electron multiplication), and its use of photoemissive surfaces which could make it useful in the ultraviolet region. Characteristics of RSS instrumentation based upon the image dissector and vidicon tubes are summarized below. Image Dissector Tube. Versions of the RSS instruments utilizing image dissector tubes have covered the spectral range from 330 to 580 nm and from 600 to 1000 nm (211) with a resolution of 1.5 nm at scan rates up to 10 kHz (20). A maximum dynamic range of 1000 was reported. It was suggested that the useful spectral range could be extended to the ultraviolet by using dissector tubes with S-l 1 or S-20 photocathode surfaces. Vidicon Tube. Recent reports have described successful applications of antimony sulfide (211 and silicon target (22. 23) tubes for RSS. The cumulative characteristics demonstrated by the reports are summarized here. The spectral range between 200 and 1 100 nm is covered, and the scan range can be varied between 40 and 400 nm with scan times ranging between 4 msec and several seconds. Each scan produces information from up to 1000 resolution elements, and spectral resolution to about 0,1 nm is possible (2.'l\. One of the instruments utilizes a portion of the photosensitive surface for background compensation (22). and all instruments average the response of several detector elements at each resolution element. In our laboratory a vidicon instrument was interfaced to a stopped-flow mixing system and a small computer. Figure 4 represents a typical spectrum of a holmium oxide glass filter. The nonlinear wavelength scale is a characteristic of the monochromator used. This background corrected spectrum compares favorably with a reference spectrum reported earlier (21 ). A linear transmittance system (LTS Model 1001 M. Technometrics, Purdue Research Park, West Lafayette, Ind. 47906) was used to evaluate the linearity and dynamic range of the vidicon tube. Typical results taken at 800 nm and at a scan speed of 20 msec exhibit standard deviations of 0.27c 7'at 957 7'and 0.00687c 7'at 0.017c T, respectively. A leastsquares fit of log response vs. log in-
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