K. Birkinshaw

Anaesthesia in a patient with an unstable neck. Morquio's syndrome.

The conduct of anaesthesia for an emergency appendicectomy in a patient suffering from Morquios syndrome who had an unstable neck has been described. A specially constructed plaster bed was used to fix the neck and an anaesthetic technique designed to deal with major airway problems was employed.

Fundamentals of Focal Plane Detectors

Spatial dispersion of ions in one dimension is a well established means of analysing ion mass and focal plane detectors (FPDs) allow ions of a wide range of masses to be recorded simultaneously. This paper is concerned with the principles governing the performance of FPDs and the types of FPD available. It is focused on magnetic sector mass spectometry but is relevant to all applications in which spatially dispersed particles can be detected rising a microchannel plate electron multiplier, e.g. ions, photons of wavelength <200 nm, electrons and energetic neutrals. Although it has proved possible to produce mass spectra with a high resolution, this has not been matched by an ability to detect them efficiently. Given that highly resolved spectra are available at the detector but are inaccessible efficiently, it is in the development of high-performance FPDs where there are enormous gains is efficiency to be achieved. Limitations of FPD performance of two fundamental types are discussed the position of impact of an ion on the FPD cannot be measured exactly, and the upper and lower count rates of the FPD are both restricted. These limitations are not simply characterized but are sometimes determined by the electron multiplier stage, sometimes by the properties of the array and sometimes by the data acquisition system.

Energy dependence of the reactions of Ar+·(2P12) and Ar+·(2P32) with N2

Abstract Rate coefficients for the reactions of the two spin-orbit states Ar+·(2P 1 2 ) and Ar+·(2P 3 2 ) with N2 have been separately determined in the collision energy range 0.04 to ∼ 0.2 eV, using a selected-ion flow drift tube (SIFDT). At 0.04 eV the quenching and reaction rate of Ar+·(2P 1 2 ) is about eight times the reaction rate of Ar+·(2P 3 2 ).

The reactions of Ar +·(2P32) and Ar +·(2P12) with H2 over the collision energy range 0.04–0.2 eV

Abstract The reactions of Ar+·(2P 1 2 ) and Ar+·(2P 3 2 ) with H2 have been studied as a function of collision energy in a selected ion flow drift tube (SIFDT). The quenching rate, kq, of the Ar+· (2P 1 2 ) state by H2 has been measured and the combined reaction and quenching rates, k* + kq, of this state was approximately three times greater than the reaction rate, k, of the Ar+· (2P 3 2 ) state. Over the collision energy range 0.04–0.2 eV, the ratio k*/k was found to be ∼ 2, which is somewhat higher than that previously measured.

A new ion detector array and digital-signal-processor-based interface

A new one-dimensional ion detector array on a silicon chip has been developed for use in mass spectrometry. It is much smaller and simpler than electro-optical arrays currently in use and in addition has a higher resolution and a zero noise level. The array consists of a one-dimensional array of metal strips (electrodes) with a pitch of 25 mu m on the top surface of a silicon chip, each electrode having its own charge pulse sensor, 8-bit counter and control/interface circuitry. The chip is mounted on a ceramic substrate and is preceded by a micro-channel plate electron multiplier. Chips are butted to give a longer array. Test results show a stable operating region. A digital-signal-processor-based interface is described, which controls the mode of operation and reads the accumulated array data at the maximum rate to avoid counter overflow.

Silicon technology in ion detection—a high resolution detector array

Abstract A new ion detecto array integrated on a silicon chip with a high spatial resolution has been designed at Aberystwyth. Integrated circuits are mounted on a ceramic substrate beneath a microchannel plate electron multiplier giving a small, light, low power, very low noise module. An array containing 384 detectors with a spatial resolution of 25 microns has been fully tested and test results are presented.

Resolving power enhancement of a discrete detector (array) by single event detection

Abstract Experiments have been performed to demonstrate the high resolving power of a discrete detector array that can be achieved by measuring and processing single ion events (speckle mode). Measurement of the spectrum of Kr + using a miniature mass spectrometer developed at the jet propulsion laboratory equipped with a focal plane detector developed at Aberystwyth show a large resolving power enhancement in the speckle mode and good agreement with tabulated peak centroids and isotope abundances. The mode of operation of the instrument is under software control and is instantly variable. This clearly demonstrates the versatility and high performance of the miniaturised system.

A study of the reactions of F+ with neutral molecules at room temperature

Abstract The thermal energy reactions of the ion F + with O 2 , N 2 , CO, NO, H 2 , CO 2 , N 2 O, SO 2 , OCS, H 2 S, NH 3 and CH 4 have been studied at room temperature using a selected ion flow tube apparatus. Reaction rate coefficients and product ion branching ratios have been determined.

Mass spectrum measurement using a one-dimensional focal plane detector

Abstract The objective of a focal plane detector (FPD) is to measure as accurately as possible the spectrum incident on it and therefore the central problem to be resolved is to relate the measured spectrum to the incident spectrum. This is a non-trivial task when the FPD is preceded by a microchannel plate electron multiplier (MCP) or other distorting element but an understanding of the characteristics can help to harness the power of the array. The measurement process for a one-dimensional array of discrete counters is analyzed and where the measured spectrum depends linearly on the incident spectrum, the measurement process has been modeled using simple matrix algebra. This model has been exploited in a number of ways outlined in this paper including the correction of non-uniformity and its extension to the non-linear region is under consideration.

Quenching of Ar+(2P12) at high pressures in an electron-impact ion source

Abstract Investigations of the non-reactive scattering of Ar+ by N2 using a crossed-beam apparatus reveal that the two spin-orbit states of Ar+ are back-scattered into different regions of velocity space (center-of-mass reference frame); this fact permits the ratio of these two states in the primary ion beam to be monitored as a function of ion source conditions. Adjustments of source pressure and ionizing current density are the key parameters which control the extent of quenching of the Ar+ (2P 1 2 ) initially formed by electron impact on Ar. Superelastic scattering of electrons is suggested as a probable mechanism and a rate coefficient, k ≥ 8 × 10−11 cm3 s−1, is estimated for the reaction Ar+2P 1 2 ) + e− → Ar+(2P 3 2 ) + e− + 0.18 eV