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The emission of positronium negative ions from Cs deposited W(100) surfaces has been studied. A dramatic change in the emission efficiency was observed upon coating a W(100) surface with Cs. The conversion efficiency (the fraction of incident slow positrons yielding the ions) of the W(100) target with a 2.2 × 10 14 atoms cm −2 Cs coverage, measured over a time interval of 3 × 10 3 s immediately after deposition, was found to be 1.25%, which is two orders of magnitude higher than that obtained for the clean, uncoated W(100) surface and 45 times greater than the highest efficiency reported thus far.

The Bratsk hydroelectric station has been operating for i0 years. The lO-yr period of observations of the behavior of the structures during operation permits checking certain assumptions and predictions made during construction [i, 3].Numerous continuing observations involving about 2500 monitoring and measuring instruments have been carried out [3]. A dlabase sheet forms the foundation for the hydraulic structures of the Bratsk hydrostation [4]. Its thickness under the channel d~n is 33-50 m and in the bank zones it increases to "i00 m. The sheet extends upstream beyond the limits of the backwater level of the hydroelectric station, its length downstream is 1.7 km and upstream 8 km. It is underlain by sandstones of great thickness.

The hydraulic structt~es of the Bratsk hydroelectric scheme (named after the 50th Great October Anniversary) include concrete and earth dams and a power station integrated with the dam, which together form a headwork 5 km long and up to 100 or 106 m high. These hydraulic structures were equipped with monit0ring-measurement instrumentation (MMI) for conducting continual observations of their condition and performance. The MMI includes a) an elevation-monitoring network of over 1000 bench marks throughout the hydroelectric scheme, six principal reference points (in rock), 25 ground reference points (along the depression cone); b) a piezometrie network comprising 600 piezometers and 28 sites for measuring seepage discharge; c) a system of monitoring-measur-Lug devices in the concrete dam, consisting of optical (on the crest) and optical-wire (along the longitudinal foundation gallery) gauges for measuring horizontal displacements, four normal and 30 inverted plummets, nearly 100 gap gauging points, and 2400 gauges.

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