Targeted collecting

Vapor pressures of phases in these systems were measured by the Knudsen effusion technique. Use of mass spectrometer-target collection apparatus to perform thermodynamic studies is discussed. The prominent sublimation reactions for these phases below 2000 K was shown to involve formation of elemental plutonium vapor. Thermodynamic properties determined in this study were correlated with corresponding values obtained from theoretical predictions and from previous measurements on analogous intermetallics. 

Equilibrium vapor pressures were measured in this study by means of a mass spectrometer/target collection apparatus. Analysis of the temperature dependence of the pressure of each intermetallic yielded heats and entropies of sublimation. Combination of these measured values with corresponding parameters for sublimation of elemental Pu enabled calculation of thermodynamic properties of formation of each condensed phase. Previ ly reported results on the subornation of the PuRu phase and the Pu-Pt and Pu-Ru systems are correlated with current research on the PuOs and Pulr compounds. Thermodynamic properties determined for these Pu-intermetallics are compared to analogous parameters of other actinide compounds in order to establish bonding trends and to test theoretical predictions. 

Vapor pressures were determined by using the Knudsen effusion technique. Effusion rates through and orifice contained in each sample cell were measured as a function of temperature by use of a mass spectrometer/target collection... 

Figure 1. Temperature dependence of plutonium vapor pressure over intermetallics as measured by target collection.

Measurement of the very low pressures associated with many of the Pu-intermetallics requires the high sensitivity afforded by target collection. To identify the gas phase species which are in the effusates, a mass spectrometer is needed. The excellent agreement between the mass spectrometric and target collection results confirms the predominance of the Pu gaseous species in the sublimation of these intermetallics. 

Mass spectrometer-target collection technique, measurement of... 

Target collection technique, mass spectrometer, and measurement... 

The vapor pressure of liquid EuC12 was measured by a target-collection Knudsen effusion method. For the congruent vaporization the pressure of EuCla(g) may be represented over the temperature range 1135-1569 K by the equation... 

In the first experiments to measure the vapor pressure of metallic Bk, using Knudsen effusion target-collection techniques, the preliminary data were fitted with a least-squares line to give a provisional vaporization equation for the temperature range 1326-1582 K, and Ai 298 was calculated to be 382 18 kJ/mol (128). The crystal entropy of berkelium metal at 298 K (S s) had been estimated earlier to be 76.2 1.3 J K 1 mol-1 (129), and later, to be 78.2 1.3 J K 1 mol-1 (124). 

Later data on the vapor pressure of berkelium metal over the temperature range 1100-1500 K, obtained by using combined Knudsen effusion mass spectrometric and target collection techniques, have been published in 1982 (124). The vaporization equations obtained were... 

P, target collection efficiency by inertial impact dimensionless... 

Time-of-flight mass spectrometry and target collection techniques over the range 1130°-1600°K. on EuCi.87 o.o7 yield a value of the enthalpy and Gibbs energy of formation 48). 

Targets Collection of targets Selected target families... 

But back to the problem of how to refer to something that is more than one or two, but not as much as a iot If you know exactly how many, you should use the proper prefix. But what if you don t know how many There are terms such as "some." And there is "several." There is a "few" and a "number of" and "numerous" and "a hand full." One desperately looks for a term that is a coiiective, but which carries the meaning of an undefined number. There are English gems such as a pride of lions and a host of daffodils. But without a specific animal or plant of reference, one must have a target collective that is appropriate, to let the term "many" or "few" imply the proper size. There were many hundreds of persons (a few thousands of persons) at... 

We have devoted a large section to the derivation of the KEMS equation, relating ion intensity to vapor pressure. As noted, it would be beneficial to understand some of the variables in this relationship further. In particular, an independent measurement of the total vapor flux would be helpful. This could be accomplished with an in situ weight loss measurement or target collection system. Improved molecular beam definition could include better positioning of the cell, with more precise x-, y-, and z-coordinates. 

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