Table of contents

Many Geiger-Muller counters are constructed and filled with bromine and argon gas in the ratios 10:90, 20:80, 30:70 and 40:60 mm of Hg and with 100% bromine to pressures of 40.0 and 100.0 mm of Hg. The plateau length of these counters to gamma irradiation is between 50 and 130 V long and is ascribed to the formation of negative ions. The 100% bromine-filled counters offer the advantages of both detecting and quenching properties and show improved stability and reproducibility and long life.

A simple electron gun deflection power supply design is presented, which can be used when high-resolution stairstep variation of output voltage, with low integral and differential nonlinearity, is required.

To improve the resolution of the authors' real-time signal processor using an acousto-optic light deflector and a position-sensitive device, another acousto-optic light deflector and a prism have been added in series. The 6-8 fold resolution is obtained by keeping the linear relation between the deflection angle and the frequency within the width of the frequency variation about 360 KHz.

An electronic hygrometer employing a capacitive sensor is described. This instrument gives a reading of relative humidity (RH) with an uncertainty of +or-2.0% at 20 degrees C and +or-3% from 10-60 degrees C over a range of 10-90% RH. This accuracy is achieved by the use of digital linearisation techniques and a separate temperature sensor to compensate for the temperature coefficient of the capacitive humidity sensor. A rapid response time of 1-2 s is achieved.

The role of stratospheric ozone in regulating the ultraviolet (UV) irradiance at Earth's surface has been widely publicised in recent years. With the publicity has come the realisation that there exist very little baseline data on either ozone concentrations or ground-level UV irradiances. This paper describes a simple, inexpensive instrument which is suitable for continuous global monitoring of the UV-A spectral region (320-400 nm).

Discusses the physical parameters for a high-power He-Ne laser working at 632.8 nm. A simple approach to estimate the optimal value of resonator length is presented.

A simplified open photoacoustic cell in which a ring-shaped piezoelectric crystal is glued to the flat side of a sapphire is described. Some spectroscopic measurements on human whole blood are presented, with the cell in a conventional mounting and with the cell mounted on a fire optic cable. The sensitivity of the simplified cell is about three times that of the previous open cells. Some applications of the simplified open cell are discussed.

An alternative solution for a portable, small-dimensional helium (or hydrogen) gas apparatus is described, which allows a high hydrostatic pressure of up to 600 MPa to be maintained at low temperatures. Some recent results concerning the application of resistance-pressure gauges at lower temperatures are presented as examples for the reliability and usefulness of the device.

Describes the design and performance of two types of ionisation chambers suitable for measuring pulse energies of VUV radiation generated by nonlinear mixing of UV laser beams. The chambers are reliable in operation and require only simple techniques for their construction.

An interference microscope is described and demonstrated. Operating on the Smartt principle (Smartt and Strong 1972) it can be made very simply using a commercial microscope objective.

The characteristics of a newly developed RF plasma jet for the crystal growth of nitrides with high dissociation pressures are described. Firstly, a newly designed ammeter utilising DC conversion is used to clarify the electrical behaviour of the RF plasma jet. Secondly, the value of RF plasma melting for the crystal growth of nitrides is confirmed by melting VN rods under the optimum conditions of 53.2 kPa (400 Torr) in Ar-N₂ plasma to indicate that the nitrogen/vanadium ratio is almost equivalent to that obtained by RF induction heating under 1.01 MPa (10 atm) of nitrogen.

A new inexpensive optical furnace is described which combines small size, compactness, adaptability, efficiency and very low thermal gradients. The unit is operated in vacuum and is designed primarily for Raman spectroscopy of molten salts, but also has been readily used for studying hot crystals. Molten samples are contained in a specially constructed silica cell which can be easily inserted and positioned inside, or removed from, the assembled furnace. Sample temperatures of about 1100 degrees C are easily attained using merely conventional resistance wire (Nichrome) as the heating element and for an input power of about 250 W.

A small and compact calorimeter capable of giving direct indication of the energy output of high-power lasers operating from the visible to the far infrared is described. The absorbing surface of the calorimeter exhibits damage threshold values in the order of 10¹⁰ W cm^-2 for 40 ns pulses of 10.6 mu m radiation and was designed to produce accurate measurements of average temperature thus overcoming the problems of equivalent heat sources. The results of a simple theoretical model describing the calorimeter are compared with the results from the practical device. The results from the model are then used to interpret the time-varying output from the practical device.

An inexpensive, versatile, feedback-controlled method of stabilising the output intensity of a pulsed dye laser over a wide range of operating energies and wavelengths is described in detail. Its likely utility in multiphoton-induced spectroscopic studies is demonstrated by a study of part of the two-photon fluorescence excitation spectrum of NO.

A new method of flash photolysis is proposed, in which the excitation and the analysis light pulses are synchronous. It is applicable to excited species of lifetime tau <or=t_E, the excitation pulse duration, while the conventional method requires tau >t_E. The synchronous method yields all the spectroscopic and kinetic parameters of interest and, while it is not intended as a substitute for the classical method, it may be useful when the transients of interest have lifetimes shorter than the pulse of the available lamp. The design of synchronous experiments is discussed.

A rapid-response ESR spectrometer operating in a new mode involving time integration of transient signals and controlled entirely by a home-built computer based on the micro-Nova microprocessor is described. Sample spectra demonstrate the unique sensitivity and resolution of the technique.

The construction and the design equations of a microwave resonator which can be used as sample cavity in a low-frequency ESR spectrometer are described. The resonator, which has the form of a re-entrant square cavity, has a Q factor of the order of 1000 and a maximum filling factor of 0.25. The resonant frequency can be conveniently evaluated using a very simple equivalent circuit which can be adapted to any shape of resonator. Four prototypes have been built and a good match has been found between the experimental values of the resonant frequencies and the theoretical ones. This agreement has been found to be particularly good for low values of the gap thickness.

A multichannel analyser link (MAL) system based on a PDP-11/03 concentrator and an intelligent serial control-bus (MAL-bus) is described. Up to sixteen multichannel analysers used in atomic physics experiments can be connected to this concentrator. The latter is used for storage of the experimental data, MAL-bus control and for the data communication with a PDP-11/70 host computer. The control software of the concentrator is also described, the emphasis being on the structure of this software. The structure is based on the method of hierarchical program development and consists of five layers. Only the bottom layer has been programmed in assembler language. The upper layers have been programmed in PASCAL.

Three basic types of membrane hydrophone made from the piezoelectric polymer polyvinylidene fluoride (PVDF) are described. These have been developed as instruments for the characterisation of ultrasonic fields in the megahertz frequency range. Performance properties such as sensitivity, directional response, membrane reflection, linearity and signal-to-noise ratio are considered for various devices made from films of thicknesses between 0.006 mm and 0.080 mm and with active elements from 0.5 mm to 4 mm diameter.

An anemometer for the measurement of the velocity of particles of different substances in a flow, separate and apart from that of the flow itself, is described. The substances are distinguished by Raman scattering. The velocity is obtained by relating the autocorrelated scattering signal to the known laser beam profile.

Changes in mass of rigid specimens, with total masses in the range 0-5 g, have been measured by the following novel method. Specimens are firmly attached to one end of a thin-walled tube which is free to vibrate; the other end is firmly clamped. Changes of mass as small as 20 mu g are indicated by changes in the frequency of unrestricted resonant flexing of the tube. The range of frequencies covered for different attached masses was 400 Hz-1 kHz. A working model has been used to monitor in situ changes in mass of specimens used as targets in sand blasting erosion experiments. A compact sensor is one of the features of the design which enables the device to be mounted in confined spaces. Operation is unaffected by the angle of inclination to gravity.

Using the modern methods of radiative temperature measurements a refined De Senarmont method (1848) is developed. It allows the measurement of the anisotropy ratio k₁/k₂ of the thermal conductivity in different directions 1,2 of an anisotropic solid at room temperature and above. This transient method is especially suited for poor thermal conductors like polymers and does also provide an estimate of the absolute thermal diffusivity.

A control device composed of a mass spectrometer and of a thermobalance adapted to glow discharge thermochemical treatment (electrothermobalance) has been developed to establish the mass balances of the reactive species during the carburising of steel by methane.

Describes a vacuum furnace made from folded tantalum tape with a volume of about 20*10³ mm³ which was designed primarily for diffusion welding of niobium parts (Zarembinski and Jarmul 1981). It was also used to prepare Nb₃Sn alloy layers on niobium (Zarembinski and Kachniarz 1982) and for soldering niobium and corundum together (see, e.g., Bogart and Ben-Zvi 1974). An advantage of the furnace is its simple construction: it can be made easily and fast. For operation the furnace must be mounted in a vacuum stand, for example a vacuum evaporator equipped with a power supply of 3 kW, 10 V.