Review of Scientific Instruments

Mechanisms for controlled approach of a probe tip toward the sample surface are essential in high resolution imaging by scanning probe microscopy (SPM). This work describes the development and performance of an inertial sliding drive capable of translating a relatively large mass (25g) at up to 1mm∕s over 1cm with step sizes of 10–250nm in ambient conditions using various wave forms as measured by fiber optic interferometry. The drive functions independent of orientation with a threshold voltage of less than 15V using a single drive signal. Use of piezotube actuators in a radially symmetric arrangement provides guided motion and minimizes differential thermal expansion between critical components. Controlled translation of the entire scanning component in both ambient and electrochemical scanning tunneling microscopy has been routinely achieved with no evidence of tip crash. This device has been specifically designed for use in in situ SPM applications where stability of the sample and that of the liquid environment are paramount.

The effect of beta-radiation from C14 has been examined on nineteen different films. The method employed uses a ``radiator,'' a set of eight radiating sources of different intensities, to replace the stable light source and absorbing wedge common in spectral photometry. With this device sensitivity and contrast of the nineteen films have been measured. Based upon these results and a microscopic estimation of grain size, recommendations are made for the most desirable film for use in radioautography and detection of radioactivity. Of the films examined, Eastman No-Screen x-ray film appears best for the detection of the beta-rays, and Ansco Reprolith, and Eastman Type M x-ray stripping films appear to be most desirable for work with radioautographs.

Over the past ten years, a variety of techniques have been proposed and demonstrated that enable the spatial discrimination and mapping of nuclear-magnetic-resonance (NMR) signals in heterogeneous objects. These NMR imaging techniques are currently finding useful application in clinical medicine and physiological chemistry, where their noninvasive, apparently hazard-free nature, and the sensitivity of the NMR signal to the state of biological tissue, are key advantages. This article reviews the historical development, the conceptual basis, and the applications of the various NMR imaging techniques. Qualitative descriptions and illustrations of each technique and an outline of imaging instrumentation are provided. Proton NMR imaging, in medicine, of pathological states such as cancer, imaging of relaxation time, chemical shift and flow parameters, imaging of nuclei other than hydrogen, and potential hazards are discussed and demonstrated with examples.

A new, high-temperature (500–1500 °C) emissometer has been designed, assembled, and tested. The apparatus is unique in that it may be used to measure the emittance of media that are semitransparent and show substantial surface roughness, internal voidage, and/or chemical inhomogeneities throughout the emitting volume. Data reduction procedures are developed and an analysis of systematic error sources and experimental uncertainty is presented. The emittance of a high-purity alumina was measured at several temperatures in the wavelength range from 2 to 14 μm. Results are compared to published values.

Some formulas for the calculation of the solid angle subtended by a circular aperture at an isotropically emitting point or spread source are presented as well as three tables of solid-angle values.

A simple method is described that permits a consistent determination of thermally induced pressure variations in a piston-cylinder, self-clamping pressure cell at temperatures less than ambient. Significant pressure changes are found to be present even for T<75 K. It is also shown that the pressure coefficient of resistance of a manganin-wire gauge is, to within experimental uncertainty, independent of temperature over the range 0<T≤300 K.