To understand ``fatigue'' or ``burn-in'' in the target of a PbO Vidicon, experiments have been made with sandwich cells of evaporated PbO. It has been demonstrated by using chopped radiation that as the PbO layer fatigues, there is an increase in short term dark conductivity. Further, it has been shown that the phenomenon is associated with loss of oxygen from the surface of the crystals during irradiation with photons. A surface chemistry model similar to one proposed by Morrison and Melnick in connection with ZnO is used to explain the observed results.

8y acceptance of this articia, th« publishar or racipicnt acknowlcdgas tha U.S. Qovarnmant'i right to ratain a nonaxclutivc, rayalty-fra* licanta in and to any copyright covering tha articia. MASTER Research sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy under contract W-7405-eng-26 with, the Union Carbide Corporation.

Experiments on tri-n-butyl phosphate solvent extraction of uranium and plutonium at-full activity levels (Campaigns 3 and 4) were conducted in the Solvent Extraction Test Facility (S E T F) , located in one of the heavily shielded cells of the Transuranium Processing Plant. The primary objectives were (1) to demonstrate and evaluate the first two cycles of the Hot Engineering Facility flowsheets (codecontamination and partial partitioning), and (2) to investigate and evaluate the use of HN02 as the reductant for tetravalent plutonium during reductive stripping operations. Secondary objectives were to determine the solvent extraction behavior of feed solutions prepared by dissolving fuel from a boiling water reactor (BWR) and to improve the solvent extraction feed clarification.

The National Transplutonium Element Production Program was established in the late 1950's to concentrate the "large-scale" production of transplutonium elements at a central location. These products are then distributed to researchers throughout the country upon the recommendations of a Transplutonium Program Committee which is comprised of representatives from the major laboratories which have an interest in transplutonium element research. The Oak Ridge National Laboratory was selected as the site for these production facilities, consisting of a high flux reactor and an adjacent radiochemical processing plant, which are capable of producing gram amounts of 252 Cf and related quantities of the other heavy elements (1). These manmade elements are all intensely radioactive and can be processed safely and reliably only in an elaborate remote handling facility, such as the Transuranium Processing Plant (TRU). This facility and some of the processes carried out therein for recovery and purification of transplutonium elements are described in other papers in this symposium (2,3,4,5). We have now made over 1000 shipments of these products to 30 different laboratories throughout the U.S. and in several foreign countries, attesting to the success of the Program. All of this would not be possible without the High FluxIsotope Reactor (HFIR) to serve as a source of neutrons to carry out the transmutation of the elements. Since first reaching full power (100 MW) on October 21, 1966, the HFIR has logged 4148 equivalent full power days through December 31, 1979, for an overall operating efficiency of 86%.During many years, this figure has run 93% or more.The purpose of this paper is to indicate the capabilities of the HFIR for transplutonium element production and particularly to dwell on the mathematical techniques involved in forecasting the composition of irradiated target materials. Also described are some of the uses to which such forecasts are put. Early work along this line was published by Burch, Arnold, and ChethamStrode (6), providing the basis for design of HFIR and TRU.

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