Table of contents

A little-known type of magnetic spectrometer, for measuring the energy of heavy charged particles, is described. The principle is due to P. H. Fowler; the source is outside the region of magnetic field, which particles enter and leave across a straight boundary; particles of different energies are brought to second-order foci at points along a line which also lies outside the region of magnetic field. The principles and the factors limiting the resolution are discussed briefly. The design and performance of an instrument built for protons of energy up to 8 MeV are described; a resolution of up to 1 in 800 in momentum has been obtained.

A considerable extension of the range and accuracy of the thermocouple hygrometer is possible in an equatorial climate, owing to the small range of variation of atmospheric pressure and temperature. An instrument, with a linear range of water vapour pressure of 10-30 mm of mercury, has been designed for use in latitudes 0 ± 5°. Systematic departures from linearity were less than 0.2 mm on direct calibration. The use of a new reference temperature close to the mean air temperature is convenient, and with it a single check measurement suffices for standardization of the hygrometer.

A photoelectric method of obtaining the angular distribution of tracks in nuclear emulsions is outlined. Details of the apparatus constructed and its performance are given. The angular resolution is about ½° and the apparatus can be made to accept tracks of minimum grain density.

A robustly constructed instrument is described which can be adapted to a wide variety of diffraction techniques. Specimen axis and counter arm are independently rotatable, manually or automatically, and are both carried by opposed tapered roller bearings. Following a predetermined programme, spectrum scanning may be performed at two speeds: slowly at angles of interest, and fast elsewhere. Graphical recorder indication of diffracted intensity can be made independent of X-ray output fluctuations by using a potentiometer reference voltage proportional to X-ray tube current.

A continuous air monitor and a portable dust sampler are described both using a new type of electrostatic precipitator. In the continuous air monitor the dust is collected on a moving aluminium tape which then passes the radiation detectors. The precipitator is operated at very low efficiency, giving a high sensitivity which is nearly independent of air flow rate. The effective drift velocity of the particles towards the collection surface is more than ten times that in the Cottrell-type precipitator.

A Linde helium liquefier-cryostat suitable for visual observations is described. It is similar to the Daunt and Mendelssohn type, but has greatly improved characteristics. Modifications have been made in the method of pre-cooling the circulating gas to 90° K and in the heat interchangers. A separate 14° K stage has also been incorporated. About 750 cm³ of liquid are produced at the rate of one litre per hour.

A magnetic analyser for accurate measurement of momentum of nuclear reaction products, employing two-directional focusing with a sector-shaped uniform magnetic field, is described. The instrument is useful for analysing particles with magnetic rigidity up to 2.10⁶ G cm (corresponding to 180 MeV protons and α-particles, 90 MeV deuterons, etc.).

Fluctuating flow-rates, total flow volumes and the frequency of an alternating flow are measured by an instrument which has been used in respiration studies on the calf. The instrument consists of three units, one, a flow-sensing unit in the form of a fine mesh gauze used under laminar flow conditions; two, a magnetic induction manometer associated with an amplifier-detector and an oscillator and three, an electronic integrator.

The flow-rate/pressure relationship of the gauze is practically linear; ±3.5 l./s producing a pressure drop of ±1.25 mm of water. The amplifier-detector output is ±9 V, d.c. for a pressure of ±1.5 mm of water; the linearity of the complete manometer is within 1%. The integrator accuracy is normally ±2½% of full scale on any of eight ranges between 0-5 l. and 0-400 l.

Steady flow-rates and total flow are indicated on a 5 in. scale panel meter and instantaneous flow-rates on an external oscilloscope. Integration time is controlled by an electric clock movement and each flow alternation is recorded on an electromagnetic counter.

An instrument is described which reads resistance values from 1 to 10⁵ MΩ on a single, approximately logarithmic scale. It is reliable, easy to operate, and immune to damage by accidental overloads.