Luther E. Preuss

Errata: A Study of the Propagation Mode for Metallic Vapors in Shadow Casting by Vacuum Evaporation of Au198 and Cr51

A special method is introduced for quantitatively determining the metal‐evaporation mechanism using metallic gold and chromium tagged with pile‐produced Au198 and Cr51. This tracer method provides a powerful tool for the study of the distribution of minute amounts of the evaporated metal. Propagation and deposition of the vaporized metal are analyzed under a variety of conditions both in the normal evaporation process and for shadow‐casting conditions. It is shown that crucible size and shape determine the evaporation‐dispersion pattern. Computation of film thickness is by quantitative tracer methods with correlating observations by electron microscopy. Structure of these metal films correlates with observations by an earlier worker [R. W. G. Wyckoff, PSA Journal 13, 12 (1947)]. The probable error of the method is ±2 percent.

81 and 31 keV 133Xe photons for soft tissue component analysis by differential absorption

The 31 and 81 keV radiations from 133Xe have been successfully used in dual beam absorptiometry for determination of tissue lipid and lipid-free fractions. The two primary radiations are amenable to filtering, and sufficient monochromaticity is obtainable for differential absorption studies. Fat and fat-free tissue ratios have been analyzed with a comparable accuracy to that found with 109Cd and 125I−241Am systems. 133Xes short half life is a disadvantage; but the penetration, low cost, and ubiquitous nature of this isotope make it a source candidate for in vivo fat-lean fraction determinations.

DEMONSTRATION OF X‐RAY DIFFRACTION BY LiF USING THE Mn Kα X RAYS RESULTING FROM 55Fe DECAY

Mn K x rays from 55Fe were diffracted with detectable intensity by NaCl and LiF powder. A special diffractometer incorporating a 100‐mc 55Fe linear source (1.5 mm × 10 mm) was used. Theoretical diffraction efficiency is about 10−5 (on the NaCl 200 plane). Diffractometer geometry provided 10−1 to 101 photons per min at the detector. This order of intensity was observed with a proportional counter, linear pulse amplifiers, and a multichannel analyzer. The three most intense beams of LiF (θ = 20° to 55°) were clearly demonstrated.

The Analysis of Mammalian Tissue into Lipid and Lipid-Free Fractions Using X and Gamma Radiation

The fat and fat-free (muscle) constituents of soft tissue have mass absorption coefficients which are sufficiently separated in the 10-100 keV range as to allow the relative proportions of each of these components to be non-destructively determined by photon absorptiometry. The use of a dual photon beam eliminates variations due to sample density and thickness, thus making the method suitable for in vivo as well as in vitro work.

Motion Picture Studies of Electron Bombardment of Colloidal Crystals

Phenomena not seen or recorded by orthodox methods are observed on the large number of micrographs which are taken during a motion picture experiment, and reaction times as short as 0.03 sec. can be calculated. The technique is useful for investigating solid‐liquid‐solid changes both by direct observation and by recording Bragg reflections. In most cases a preliminary effect of electrons upon crystals is to drive off water. In the case of sodium chloride crystals a residual envelope is left. Inside this, small particles, both solid and liquid, are observed to move rapidly due, it is believed, to a combination of Brownian movement and convection. These gradually evaporate and diffuse through the wall. The possibility is discussed that the residual envelope is formed by contamination. Examples are also taken from bombarded, colloidal crystals of tungsten oxide.

A Technique for Taking Motion Pictures of Electron Microscope Images

Lately, for the first time, a technique for taking motion pictures of electron microscope images has been developed which is proving useful in the study of some of the effects of electrons upon matter and particularly upon colloidal crystals. Resolution of 150 to 300A is achieved and is suitable for a host of practical electron microscopical problems. Pictures are taken from outside the instrument, utilizing the radiation emitted by the fluorescent screen. Some instrument adaptation is required for adequate illumination, and precautions must be exercised against toxic x‐ray dosages.

Iterative method for elimination of the Kβ filter in dual‐beam differential tissue absorptiometry

The application of a dual photon beam to the measurement of tissue and tissue-like substances has generally required the use of a filter to attain the required monochromaticity of the lower-energy x-ray photons. In many cases this has the undesirable effect of also severely attenuating the desired low-energy beam. A method for circumventing the use of the filter is described. The technique relies on a knowledge of the initial intensities of the components of the x-ray portion of the dual beam and involves an iterative mathematical procedure. Experimental verification of the method using both tissue and nontissue substances has been carried out. R values obtained with the iterative system show good correlation with filtered values.

Image formation of a high temperature vacuum evaporation source through combined distillation camera exposures and autoradiography with Au198, Cr51 and W185

Abstract A combination of vacuum distillation self-imaging and autoradiography is described for the production of an image of the vacuum evaporation geometry of an evaporating source at the instant of molecular distillation, or during selected periods throughout the distilling sequence. The mode of the macrodistillation phenomena may be ascertained by the method, which is particularly applicable to the study of distillation phenomena of minute masses of charge material. The system provides an image, the density of which quantitatively represents the intensity of the evaporation rate from any point on the distillation source. A shutter system may be used to provide discrete images of the distillation phenomena at limited, selected time periods throughout the evaporation. The method consists first of the use of a simple vacuum distillation camera. The image of the source being formed on a cold target plate at the image plane and made up of the condensed metal distilland, tagged with its radioactive isotope. Single isotopes or combinations of the tagged metals may be used in the crucible and charge. Radioisotopes used here are Au198, Cr51 and W185. The metallic condensed metal in image array may be so tenuous as to be invisible on this target plate. This condensed tagged metal is placed in gross apposition with a proper autoradiographic emulsion and the resultant photographic negative presents the true image of the distillation intensities at the source. This image may not necessarily coincide with the geometric, mechanical limits of the filament plus charge. The autoradiographic image reproduces the apparent source seen by the target. This special benefit of the method, in that it demonstrates the source region from which the distilling atoms emanate, allows study of wetting phenomena, creep of charge, reflection and distilland scattering phenomena. Image photographic density may be a quantitative measure of the source distillation rate, when the photographic process is standardized. The method has potential in binary isotope distillations to determine simultaneous evaporation phenomena of charge and crucible. The methods resolution theoretically extends to the order of 10 μ and has a sensitivity down to 500 μg charge mass distilled. Source images may consist of as little as 10−10g of metal for certain beta emitters.

109Cd in body composition assay: considerations of error and reproducibility

Absorptiometric studies were done using 88 and 22 keV photons on simulators and tissue, in vivo and in vitro, to establish the limits of error and reproducibility in fat to lean ratios. Theoretical and measured R values for various phantoms were shown to exhibit agreement to 1%. Two component discrimination was established to 1.5% of prediction and thickness independence verified. Assays of varied lipids demonstrated highly consistent R values. Assays of tissue fat, in vitro, extraction verified, showed an error of 1%. Reproducibility of triceps assay on living human subjects was good. Coefficient of variation was subject dependent but typically was less than 2%.

The Potential and Application of the Synthetic Radioactive Isotope in Vacuum Research and Technology

A brief outline of the uses, to date, of the radioactive nuclide in basic vacuum research and routine technological application, illustrates that the tracer tools initial emphasis, in vacuum work, has been predominately in the realm of the distillation phenomena. Some examples of the radiotracer system applied to vacuum evaporation of nuclides, are given. The modes of availability for synthetic radioactive isotopes are reviewed, along with the restrictions imposed on their use in vacuum study by their characteristics of half-life, radiation type, specific activity, etc. The methodology and some examples of health-physics procedures, vacuum system alteration, and essential techniques of radiotracer work are dealt with, along with usefulness of ancillary techniques, such as the autoradiographic method. A brief critique is made for the potential of the radiotracer technic, and its attendant sensitivity, for specific vacuum studies.