Beam Assembly Research Articles

Wide Range Continuous Mercury Vapor Monitor

ABSTRACT The mercury vapor monitor, MDC-1-01, described in this paper is the first prototype in the MDC series. It was designed and developed in our laboratory to measure airborne mercury vapor on a “continuous” basis in the range of 400 ng to 20 mg mercury per cubic meter of air. In comparison with other instruments, commercially available, it uses much improved principles as regards electronics, optics, and chemistry [l]. The double beam assembly, in combination with a selective filter, permits the measurement of mercury vapor in the presence of the most commonly encountered organic vapors and dusts. Practical applications are discussed.

Effects of a Modified Wehnelt Grid Assembly on Electron Microscope Image Contrast

The need for higher brightness electron sources with improved coherence has been appreciated for some time by electron microscopists and electron optical manufacturers. The results given in this paper suggest that changes in these electron source characteristics can be expected to influence the image quality of lattice defects taken under two-beam dynamical conditions in thick crystals.In this study stacking faults and bounding partial dislocations in silicon were imaged at various crystal thicknesses using JEM 200 electron microscopes operated at 200 kV. linages were, obtained using microscopes equipped with a normal Wehnelt grid assembly and a modified assembly. In both cases a standard hair-pin filament was used. The modified Wehnelt assembly (so-called Cool beam assembly) differs from the normal one both in shape and filament position.

Hydrogen and Nitrogen Desorption Phenomena Associated with a Stainless Steel 304 Low Energy Electron Diffraction (LEED) and Molecular Beam Assembly

The rates of hydrogen desorption from the walls of a standard LEED stainless steel vacuum chamber isolated from the ion pump have been measured using an oxygen-free copper orifice of known conductance, which acts as the final focussing slit in a molecular beam assembly, and found unacceptably high for the maintenance of a clean metal single crystal surface. The causes are discussed and the rates of desorption are presented after the stainless steel apparatus had been subjected to vacuum degassing at 850–950 °C in a vacuum furnace at pressures ≤10−5 Torr. Desorption rates are decreased ∼130 times. Rates of desorption of nitrogen from Varian post-acceleration type two and three grid LEED optics screens (P-4 CR 422 phosphor) have been measured. Possible displacement reactions with residual hydrogen, small quantities of which are adsorbed during nitrogen desorption, are discussed. It is concluded that the two processes are independent of each other. Contamination of the single crystal samples with the nitrogen desorbed for the LEED screen is also discussed. Brief reference is made to the adsorption properties of stainless steel 304 with special reference to hydrogen and nitrogen.

A technique for accurate specimen temperature measurement in a thermobalance

A null method is described by which specimen temperatures in a thermobalance may be accurately recorded. Split planes and knife edges of stainless steel are used on the balance beam assembly to provide a conducting path from a noble metal thermocouple in contact with the specimen to a potentiometric recorder. The technique has been tested at temperatures up to 650°C by comparison against standard melting points and an accuracy to ±1 degC was obtained over the whole range.

Improved recording vacuum balance

This paper describes the construction of a recording electromagnetic vacuum balance with an improved form of control circuit. It was originally designed for the gravimetric determination of adsorption isotherms and measurements of the rate of adsorption on porous solids, but it has proved equally suitable for other applications where rapid changes of sample weight have to be recorded against time. The control system is entirely electronic, and the entire beam assembly and suspension is housed in a vacuum jacket of total capacity of less than one litre. The variation of load corresponding to full-scale deflection of the pen recorder can be varied between 10 and 600 mg with a reproducibility to better than 1%. An electrical zero shift allows the starting point of the scale range to be adjusted by about 50% of the full-scale deflection to allow for variations in the initial weights of samples. The zero setting and the sensitivity of the balance have negligible long-term drift.

Discussion of Design Factors in a Spring-Trip Beam Assembly for Moldboard Plows

Discussion of Design Factors in a Spring-Trip Beam Assembly for Moldboard Plows

Discussion of Design Factors in a Spring-Trip Beam Assembly for Moldboard Plows

Discussion of Design Factors in a Spring-Trip Beam Assembly for Moldboard Plows

Design Factors in a Spring-Trip Beam Assembly for Moldboard Plows

Design Factors in a Spring-Trip Beam Assembly for Moldboard Plows

A vacuum microbalance for measuring sorption in dielectrics

A balance for measuring the rate of sorption of water vapour by non-polar dielectrics is described. The beam assembly, which is constructed from hard glass, is contained in a vacuum tight brass case, and a fused quartz torsion fibre is used to measure the change in weight. An expression for the sensitivity of the balance is derived. With a load of 0.1 g a change of weight of 0.02 μg is indicated and a maximum change of 300 μg can be compensated by the torsion control.