Table of contents

The author considers methods of detecting fingerprints on a wide range of materials commonly found at the scene of a crime, with particular emphasis placed on the newer autoradiographic techniques. This is set against a description of studies on the fundamental nature of the latent fingerprint and its host substrate, with a brief review of the history of reagents used in latent fingerprint examination.

The mechanics of the formation of fingerprints is discussed as well as results of microscopic observations that have led to an understanding of the interaction of fingerprints with flat surfaces. Measurements of contact angles, optical properties and electrical properties of fingerprints are also described. Work on the mechanics of powder adhesion to fingerprints is reported along with two electrostatic methods of fingerprint development. Fingerprints can be developed in vacuo by metal evaporation. Research on the mechanism of this method is discussed.

This device uses counter-rotating Perspex blocks to measure the diameter of the pupil of the human eye. The instrument is accurate to +or-5%, gives direct readings on a linear scale and is suitable for use in drug studies.

A description is given of some improvements and modifications to an apparatus (Bradley et al. 1974) using a computing counter, as well as an appraisal of the problems that arise for more highly conducting samples. The apparatus used basically consists of an oscillator, incorporating a calibration capacitor using air and quartz dielectrics.

A new method is proposed, by which a pressure of the order of 10¹⁰ Pa or more can be estimated by observing the change in decay rate of radioactive nuclei embedded in a pressure device. The radioactive sources ^99mTc and ⁷³Ga are used in the procedure.

The system described consists of two separate glass cryostats: One is a traditional N₂ shielded He cryostat, for temperatures below 4.2K; the other is a special gas-flow cryostat, for temperatures above 4.2K. With a simple regulating system, the temperature stability of the flow cryostat is 1K. The helium consumption is 0.2-0.31 h^-1.

Unbacked films 0.2-0.4 mu m thick have been prepared. The films are opaque for He I radiation (21.2 eV) but transmit up to one-third of He II radiation (40.8 eV). Beryllium filters 6 mm across have been mounted inside the tube of a discharge lamp where they can be slid in and out of position. The films were prepared by evaporating beryllium from a tungsten crucible on to a thermoplastic resin substrate at a rate of 10 nm s^-1. Initial vacuum was 4*10^-5 Pa, and 4*10^-4 Pa during evaporation. The plastic was dissolved and the film floated on to a washer.

A circuit which allows the OZ4 germicidal lamp to be chopped electronically at frequencies between 5 Hz and 5 kHz is described. The waveform of the chopped radiation has a rise time of 20 mu s and a pulse-to-pulse reproducibility of better than 0.5%. In addition, the light output is phase-related to the input chopping signal, so that the device is convenient to use with phase-sensitive detectors.

This device employs a well shielded magnetic field to separate electrons from negative ions, and is used in electron-molecule collision experiments in conjunction with an electrostatic energy analyser. It enables the weak current of negative-ion fragments originating from dissociation processes to be distinguished from the large signal caused by scattered electrons.

A novel approach is described for the design of high-voltage fast pulse generators. It is based on a combination of a stacked line transformer (SLT) and a coaxial Marx circuit, whose principles were successfully applied for the design of a 600 kV, 25 ns repetitively pulsed generator.

A simple electrolysis cell of small capacity has been constructed. A needle valve system maintains a constant pressure in the cell enabling the electrolysis of heavy water to continue for hours without attention. The system also eliminates the exposure of a large amount of mercury to the atmosphere. 160 ml h^-1 of D₂ gas at normal pressure are collected in the reservoir under vacuum at a current of 0.4 A through the cell. Deuterium prepared in this way can be used as an RF ion source.

Observations are made of standing-wave ratios in a slotted line terminated by the test cell. The final solution of the impedance equation with respect to epsilon ' and epsilon " requires iterative calculation of Bessel functions. The method requires only a small volume of the sample and gives satisfactory accuracy for polar liquids. An error analysis of the results is performed to determine the confidence interval of this method.

As well as having a conventional capability in analogue signal capture and regeneration, the instrument has a complete 'split store' capability which allows direct visual intercomparison of two stored waveforms. Also incorporated is the ability to scan the contents of the memory with an 'analogue scan' input signal. Access can be gained directly to the memory via a digital interface for the loading or recording of data. The instrument has a selection of significant and diverse applications: the creation of a Josephson junction SQUID analogue, source levelling and sophisticated measurements on a stepping motor.

A rotation-free magnetic electron lens doublet of high magnification is described which is suitable for a transmission electron microscope. In addition a distortion-free image can be obtained at low magnification. The doublet is of unusually compact form, made possible by the development of miniature lens windings operating at high current density. Such a design can be scaled up exactly for employment in a million-volt electron microscope. The resulting scaled-up lens is comparable in size with conventional lenses for a 100 kV electron microscope.

A rotor with four mica wings serves as a sensor in an annular magnetoelectrolytic cell for the measurement of threshold pulses for the onset of magnetohydrodynamic (MHD) motion. The pulses are generated by capacitor discharge within a capacitance range from 100 pF to 100 mu F and a voltage range up to 4 kV. Signals obtained by increasing the amplitude beyond the threshold are photographically recorded. Proportionality between the momentum induced and the momentum recorded is found for neutral salt solutions. Increasing dilution leads to a non-MHD dipole effect in distilled water.

Space charge effects within the analyser are shown to cause saturation of the output signal for entrance slit widths wider than some value W_ent^max, and the variation of W_ent^max with ion energy E and charge Z is measured for the ions C⁶⁺, C⁵⁺ and C⁴⁺ in the range 0.75 keV<or=E/Z<or=3 keV. Comparison is made with theory. An ion energy spectrum distorted by space charge effects is contrasted with the same spectrum free of such effects.

The use of a triangular cyclic interferometer for obtaining two counter-propagating optical beams which are accurately collinear is described, and its performance including the tolerance sensitivity is analysed. A novel technique for facilitating fringe observation has led to the realisation of an instrument with a demonstrated angular alignment capability of 1 mu rad. The new design permits real-time monitoring of the interferometer. The whole alignment operation of the interferometer relies on visual observation of interference fringes.

The Doppler frequency shifting of reflected light is achieved by a moving mirror. By adopting an optical control system for driving the mirror, tunable frequency shifts over a range from 500 Hz to 30 kHz have been obtained and the long-term drift for a given frequency offset has been sufficiently stabilised. As a typical result, it is found that the frequency drift over one week is +or-3 Hz at a frequency shift of 3.16 kHz, and the spectral broadening is 1.0+or-0.2 Hz.

A resistor-heated all-metal ultrahigh-vacuum furnace used for argon extraction in ⁴⁰Ar-³⁹Ar dating is described. Compared to conventional extraction systems, the main improvements of the new furnace are: low amounts of argon released in blank runs, ease of maintenance, and reduced health hazard during experiments with radioactive samples.

In the Fizeau method for measuring the thickness of a thin film the reference flat often pivots on a dust particle. The local surface distortion which results is shown to be proportional to the applied force and inversely proportional to the distance from the pivot. For a pair of fused-silica flats subjected to a force of 1 N, the total distortion is approximately 10 nm at a distance of 1 mm from the particle.

An automatic Langmuir-type surface balance for studies in a UV or ionising radiation field has been designed. The apparatus is suitable for measurements of the following functions: pressure p=p(A), potential V=V(A), area/molecule A=A(t)_p, V=V(t)_p, p=p(t)_A, V=V(t)_A where t denotes time, in the temperature range 278-313K maintained to within +or-0.5K. The sensitivity of the balance is 0.1 mu N cm^-1 and this value is limited chiefly by the quality of the anti-vibration arrangement. A new design of the surface electrode minimises the influence of radiation from the ionising source upon the film. Examples of monolayer behaviour and other tests are presented.

The characteristics of the Barkhausen signal from thin magnetic films are discussed and the requirements for analysing equipment are derived. Direct digital recording of the signal is difficult because it requires a sampling frequency of 1 MHz and a storage capacity of about 10⁷ bytes for one measurement. However, the special form of the signal permits an information reduction of about 10², making it possible to record one measurement on a tape with 130 kbytes. The analysis is performed in the computer by regenerating the original Barkhausen signal. Using this method and the right software, all the information can be obtained from the pulse signal.

A silicon semiconductor detector spectrometer for the study of stopping power and straggling of alpha particles in liquids is described. The absolute thickness of the liquid layer has been measured using a Michelson interferometer and a micrometer, the experimental set-up being kept in a temperature-controlled room. A specially designed collimator houses the alpha article source (²⁴⁴Cm) employed for measurements in water and a tissue-equivalent liquid. Sample results for water and tissue-equivalent liquid are presented.

An apparatus is described whereby an argon matrix is deposited (together with a species of interest) by conventional matrix isolation techniques in a small, efficient, separate continuous-flow helium-cryostat and then injected in vacuo, into a large standard split-pair superconducting magnet cryostat. During injection the sample does not warm above 20K and the vacuum space around the sample is then filled with liquid helium or exchange gas. A critical example of the value of the technique is given with Zeeman anisotropy of the sharp line emission of Cl₂ in argon detected at about 13600 cm^-1.

Transaxial tomography is a radiographic technique that provides an image of a selected two-dimensional section of a three-dimensional object. The present paper describes a new analogue recording system that uses a fan-shaped X-ray beam and a built-in photographic summation technique for image reconstruction. The performance of the camera is illustrated with different test samples.

A finite-length hot-wire anemometer sensor, operated in air at a very low overheat ratio so as to act as a resistance thermometer does not respond to stream temperature perturbations with frequencies near the wire's corner frequency, like a single time-constant system, that is, a simple pole. This is contrary to presently available theoretical predictions based on the assumption of constancy of temperature at the wire ends under dynamic conditions. A simple lumped-parameter model is postulated which introduces a transition zone at the ends of the wire with a corner frequency different from that of the wire thus permitting the temperature of the wire ends to fluctuate.

An apparatus is described for in situ electron spin resonance tensile testing of polymers, enabling radical formation to be recorded simultaneously with stress-strain data from the mechanical tests. The operation and performance of such an apparatus using a large-access cylindrical cavity are described together with results obtained by low-temperature deformation of cross-linked elastomers.

A procedure for the optimum design of a superconducting magnet with two square-ended solenoids is presented. The solenoids may be wound from different materials and carry different current densities. A major reduction in cost has been achieved. A sample calculation is given for 9.2 T and 16 T solenoids.

A simple electrical isolation device is described, which incorporates an insulating porous core to assist in electron-ion recombination. Designed for isolating an ion thruster from its mercury propellant feed system, it has resulted in stand-off voltages in excess of 7 kV at normal operating mercury vapour pressures. Breakdown investigations, leading to the final design, have been included and these show that operation as a controlled high-voltage switch is possible. Some of the life-limiting operating factors have been identified.

Sensitive ballistic and torsion pendulums, capable of measuring momenta of 3*10^-9 N s, were developed. They were used for measuring the momentum transfer to a solid target irradiated by a 1.06 mu m high-intensity laser and the angular distribution of the momentum in the blow-off plasma.

A simple design for a transversely excited atmospheric pressure (TEA) nitrogen laser capable of repetition rates up to 100 Hz is described. Commercial-grade N₂ is blown through the open laser channel so that no vacuum system is necessary. Without any mirror the laser provides UV outputs ( lambda =337.1 nm) at both laser ends with a total average power of up to 23 mW. Using one of them to pump a Hansch-type dye laser and the other to synchronously pump an amplifier we obtain, with rhodamine 6G as the lasing dye, tunable pulses with an energy of approximately 1 mu J and a bandwidth of less than 0.07 nm.

The application of a two-dimensional diffraction array to the measurement of wire-cloth screens has been treated by Chapman and Butland (see ibid., vol.10, p.621 (1977)). Here the interference-diffraction pattern of such an array is analyzed in the Kirchhoff approximation according to the Babinet principle. It is shown that the confusion arising from the indistinguishableness of the diffraction patterns of the two complementary arrays does not involve a breakdown in the Kirchhoff theory.

The well established method of fabricating neutron collimators using Melinex foils (see ibid., vol.10, p.543 (1977)) has been extended by the use of enriched ¹⁰B coatings so that they perform efficiently at neutron energies in excess of 0.32 eV. These collimators have a triangular transmission function and their degree of perfection was measured to be 0.80, which is a considerable improvement on that possible prior to the use of the stretched plastic technique. It has been shown that the energy range over which the gadolinium-oxide-coated collimators perform efficiently is 0-0.12 eV.

A spark erosion technique capable of producing accurate metal spheres, and described by Muirhead et al. (see ibid., vol.9, p.872 (1976)) is applied to a single-crystal specimen of gadolinium-yttrium alloy. X-ray back-reflection Laue photography is used to show that the method does not damage the crystallographic structure.