Table of contents

The focal properties of electron bombardment ion sources of the type commonly used in mass spectrometers are calculated by numerical ray tracing. Low electron current density conditions were assumed so that the effect of space charge within the electron beam could be neglected. Calculation of paraxial rays show that one, two or three real images can be formed within the ion source, depending on the voltage applied to the source electrodes. A curve relating the source sensitivity to the repeller voltage is computed by using ray tracing to a higher order of approximation; the theoretical curve displays the same characteristics as those of the curve obtained experimentally on the AEI MS902 mass spectrometer. This treatment demonstrates that the structure of the repeller curve is related to the multiplicity of real images that can be formed within the source. Precise mechanisms determining the source efficiency are deduced from the computed focal properties.

A detector has been made using a guard-ring photodiode and a phosphor disk and the reproducibility and stability of the phosphor examined. The absolute quantum efficiency of the detector at wavelengths between 584 AA(0.65%) and 1216 AA(0.83%) has been obs. using a thermopile and a rare gas ionization chamber. The theory of a new mode of use of the ionization chamber is developed.

General expressions are obtained for the response of a steady-state oscillator to nuclear magnetic resonance. In particular, it is shown that the amplitude modulation and frequency modulation both give a mixture of chi ' and chi ". In the fm case, the chi " contribution depends on the 'dephasing' of the feedback current and may be quite large in practice, especially at high frequencies. In the am case, the chi ' contribution is normally small (<or approximately=1%) but may be much larger for low Q oscillators. Excellent agreement between experiment and theory is obtained using a specially constructed Robinson oscillator.

A method is described which enables the direct measurement of relaxation times and relaxed and nonrelaxed heat capacities as a function of temperature. The apparatus designed is to be used as additional equipment to the Perkin-Elmer differential scanning calorimeter DSC-1B. The specimen is heated periodically with time instead of proportionally. The amount and phase of differential heat flow are measured. The parameters of an 'equivalent circuit' of a heat capacity model are fitted to the measured complex C_p values obtained at various frequencies and appropriate amplitudes of temperature. Further applications of the 'oscillating thermal analysis' are proposed.

Both the 'frequency domain' and the 'time domain' methods for analysing the signal from a laser velocimeter are discussed and expressions are derived relating the velocity resolution and the response time of the instrument.

A simple, efficient optical arrangement for the laser Doppler velocimeter is described which requires no optical heterodyning alignment, and is extremely quick and easy to set up in experimental work. It has the additional advantages of measuring two-dimensional flows, and ease in traversing the flow systems. The system is stable and insensitive to stress and vibrations.

Weight functions are derived for the circular channel and the rectangular channel transverse field magnetic flowmeters. A weight function determines how the voltages which are induced by the flow in the channel of a conducting fluid through the transverse magnetic field of the meter, contribute to the output signal at the meter's electrodes. It is a function of the channel geometry and the relative size of the meter's electrodes. The weight functions are derived by means of Green's theorem and conformal mapping. Green's theorem is used to show that a weight function is equivalent to the electric field for a particular electrostatic problem which has a configuration identical to that of the flowmeter channel. Solving for the weight function of a two-dimensional rectangular flowmeter, this paper then uses conformal mapping to determine the weight functions for two practical configurations: the two-dimensional circular flowmeter, and the rectangular flowmeter with finite length electrodes. Weight function contour plots are presented for both of these cases. The circular channel weight functions are given for electrode span angles of 5 degrees , 45 degrees , and 90 degrees . The rectangular channel weight functions are for electrode length to channel width ratios of 0.01, 0.1 and 1.0.

In order to eliminate the problem of calibration in beam spot size measurements, a wide slit scanning technique has been developed. As the beam scans across the edge of a slit, the ions or electrons are collected, and the resulting signal is displayed on an oscilloscope. This trace is a two-dimensional picture of the convolution of the beam with the slit edge. A mathematical analysis of the signal allows the intensity distribution of the beam to be obtained. Experimental verification of the technique is described.

A quick, versatile and moderately sensitive instrument for measuring the effects of time, temperature and direct or alternating magnetic field on the remanent magnetization of rocks has been constructed. The instrument combines in one unit a ballistic magnetometer, a furnace, a solenoid and nulling coils. The ability to operate the solenoid at any sample temperature on ac as well as dc is a new feature; in addition the capabilities of the other components are significantly improved over previous instruments of the same type. The magnetometer, incorporating a galvanometer amplifier, reliably measures magnetizations of 10^-5 e.m.u. per cm³ or larger. Experiments which can be performed without removing a sample from the instrument include: production and measurement of isothermal, viscous, anhysteretic and thermoremanent magnetizations; continuous thermal demagnetization without intermediate coolings; alternating field demagnetization and hysteresis measurements at ordinary or high temperatures.

A continuously variable monochromator with a half-width bandpass of 7.2 nm is described. Two graded filters are used, and although the transmittance is low, the exit slit can be opened to emit a flux of monochromatic light not easily obtainable with the same purity from a single graded filter, nor from a conventional prism of grating instrument of comparable dimensions.

A circuit is described which enables the load angle of a synchronous machine to be measured, recorded and displayed with a much shorter time delay than comparable methods previously discussed. The use of solid-state circuitry and integrated-circuit operational amplifiers provides a very compact unit, and the versatility arising from the adoption of switching-circuit techniques enables the basic circuit to be readily applied to phase angle or power factor angle measurements in an ac system.

A computer controlled operating and data acquisition system for a quadrupole mass spectrometer is presented. The overall system carries out on-line chemical analysis of combustion gases in a rocket- chamber. The computer controlled mode of operation is based on supplying the quadrupole control console with an externally generated control voltage to tune the instrument to the mass numbers that are of interest. In this manner, only the peak heights of the mass numbers of interest need to be recorded, rather than a complete spectrum. The operation consists of a calibration phase and a run phase. In the calibration phase, the exact control voltages for all mass numbers are determined. The control voltages drift with time, and in the run phase, nine slight different values are supplied around the calibrated control voltage to insure that the peak is not missed. Thus, only nine data points are recorded for each preselected mass number. Immediately after each test series, a snapshot dump of one scan is printed out in the test area. The quadrupole output is recorded on digital tape and subsequently processed by an IBM 7094 computer to yield the relative concentrations of the desired components. The system described here can be used in any application where the fast scanning capability of the quadrupole is of interest.

A method is described whereby the thermal conductivity of a pressed powder sample is measured with an ordinary type differential thermal analysis apparatus. Provided that the corrections for the heat leakage and for the errors from thermocouples are carried out, it is found that the DTA method can be used for obtaining rough values of thermal conductivity easily with small amounts of the sample.

An air bearing work feed for an abrasive saw is described which is used in the cutting of semiconductor materials. Silicon wafers sawn on this sensitive work feed shovrr improved surface finishes and a reduction in cutting damage.

The use of an integrated circuit TTL monostable module for producing signal delays for pulsed nuclear experiments is described.

Measurements have been made with dual gate MOS field effect transistors when immersed in liquid nitrogen. It has been found that such devices are suitable for wideband and tuned rf amplifiers, with improved characteristics. Simple practical amplifier circuits and their characteristics are described.

An inexpensive silicon photovoltaic detector has been used in this laboratory for detecting weak transient absorptions for lifetimes to greater than 10 mu s in the wavelength range 0.6-1.15 mu m after flash photolysis of liquids and plastics. No cooling is necessary and transient optical densities of 0.001 can be measured with an uncertainty of +or-20%.

A simple device for crystal growth is described. It consists principally of a cryostat cooled by a pulsed stream of liquid nitrogen. The cryostat has been operated between 0 and -150 degrees C. The temperature can be maintained constant to within +or-1 degC and the liquid nitrogen consumption is of the order of 1 1h^-1 at -100 degrees C.

A pressure switch is described which enables individual pressures to be selected for measurement from up to 40 input pressures. The device depends upon the use of clamped rubber tubes and is compact and reliable.

Two methods are discussed which can be employed individually or in combination to reduce two sets of data points representing sinusoidal signals of equal, and very low, frequencies. The phase angle between the signals as well as their amplitudes and average values can be determined. One method is based on a least squares analysis, the other utilizes the geometrical properties of the Lissajous figure obtained from the sets, when combined in one coordinate system.

By binding oxide ceramic and metal with solder glass it is possible to make bakeable support insulators with machineable insert pins or end caps.

Describes a solid state current amplifier with which a flame ionization detector can be used at all practicable sensitivity levels. The use of metal-oxide-silicon transistors in a conventional circuit gives a degree of stability significantly better than that achieved with thermionic electrometer valves. The amplifier has a sensitivity of 100 mV pA^-1 and a noise output equivalent to 2*10^-15A rms at the input; thermal drift is typically 1 mV degC^-1.

The design and operation of an improved spray chamber fur use in analytical spectroscopy is described. Gas mixing and large drop removal is achieved by passing the aerosol through a construction which functions as a turbulent jet. Noise level comparisons between chambers of different geometry is made by using a strip chart recorder which meters the signal from a commercial atomic absorption unit for standard copper and cadmium solutions. Hence the improved geometry is determined and should lead to improved detection limits in atomic absorption spectroscopy and flame photometry.

A four-point probe apparatus, suitable for measuring the electrical resistivity of plane parallel slabs of semiconductors, is described. The probe arrangement consists of two pairs of probes; a probe pair contains a central needle-shaped electrode which carries the current and an outer concentric tubular electrode which is used for measuring potential; the probe pairs are placed on opposite faces of the slab with the needle electrodes on the same axis.

Frequently it is necessary to measure both velocity and temperature in the study of fluid mechanics. The use of a constant temperature hot wire anemometer to measure these two properties simultaneously in air is described below. The results were accurate within 1.3% based on temperature measured in degrees C, and the computer time required per temperature and velocity point was about ¹/₂s.

Describes a sensitive liquid-level gauge or micromanometer which can detect level changes of 0.01 mm water. It is essentially a vessel suspended on a spring and connected to the container in which the liquid level is measured. It amplifies the level changes mechanically and actuates an electrical transducer.