Ulrich Wolfgang Arndt (1924-2006)
Ulrich Wolfgang Arndt was born in Berlin in 1924, to parents with mixed German-Russian-Dutch origins. His family moved to London in 1936 to escape the increasingly repressive atmosphere in Germany, and Uli went to school at Dulwich College. After initially specialising in Classics, he switched to science, in spite of the fact that this was held in low esteem by many at the time. Following another family move, he finished his schooling at King Edward's School in Birmingham and spent a year at Birmingham University before going to Emmanuel College, Cambridge to read Natural Sciences in
While still at Birmingham, Uli had met Max Perutz briefly following an introduction by family friends. Uli greatly enjoyed his time in Cambridge, and took full advantage of the many College and University societies, being particularly active in the Emmanuel Debating Society. Because of war-time restrictions, he was allowed to spend only two years at Cambridge, and after obtaining a first at the end of his freshman year opted to complete the Tripos in two years rather than the usual three. Despite recording the best Physics Tripos of his year, his final degree was only a II-2, but this did not prevent him from enrolling as a PhD student in the Crystallography Department of the Cavendish Laboratory, then run by Henry Lipson. His work involved characterising iron-copper-nickel alloys using a Debye-Scherrer powder camera. Uli quickly decided that the photographic methods in use at the time were too tedious and inaccurate, and decided to build a diffractometer equipped with a Geiger counter to do the job. Making extensive use of Government surplus supplies, he succeeded in his task by the time he left Cambridge in 1948, but unfortunately had not recorded sufficient experimental data to write up his thesis.
He then joined Wally Hall at Birmingham University as a Research Fellow, and drew on his experiences at Cambridge to design and build one of the very first precision diffractometers. This finally yielded sufficient material for his thesis, although all the writing had to be done in his spare time.
In 1949, he moved to London to join Dennis Riley at the Royal Institution. Here he developed a compact rotating anode generator and several automatic diffractometers for low angle diffraction, again making extensive use of Government surplus equipment. Realising the limitations of Geiger counters, he developed some of the first proportional counters, making use of equipment from the vaults of the RI left over from Dewar's work on liquefaction of gases. Following Pauling's publication of the alpha-helical model for proteins in 1951, Uli and Dennis were able to determine the radial distribution function of bovine serum albumin and found excellent agreement with that predicted by Pauling's model. This provided some of the first experimental support for the alpha-helix, although subsequent work showed that the agreement was largely fortuitous! Lawrence Bragg's arrival as Director at the RI led to a change in focus towards single crystal diffractometry, and a very fruitful collaboration began with David Phillipsin 1955. This led to the development of the linear diffractometer, controlled by an analogue computer, which was used to collect some of the data for Kendrew's 5Å resolution structure of myoglobin.
A collaboration with Terry Willis at Harwell resulted in a greatly improved version of the diffractometer for neutron work, and an X-ray version of this instrument was subsequently commercialised very successfully by Hilger and Watts. Uli and Terry's collaboration also led to the publication a few years later of the classic monograph "Single Crystal Diffractometry".
Uli's pioneering work in instrumentation and automation had not gone unnoticed, and in 1962 Max Perutz invited him to join the newly founded Medical Research Council Laboratory of Molecular Biology in Cambridge. Uli took up the invitation the following year. The challenge of measuring the many thousands of reflections required for protein work led him to re-examine the possibility of using the only two-dimensional detector available at the time, namely X-ray film. This in turn led to the development of automatic densitometers to speed up the measurement of film data recorded with precession cameras. Uli soon realised that the availability of scanning densitometers eliminated the requirement for the spots to lie on straight lines, opening up the possibility of using screenless oscillation photography. In the late 1960's Uli's PhD student, Paul Phizackerley, investigated the potential of this method, and this led to the development, with Alan Wonacott, of the Arndt-Wonacott oscillation camera, marketed by Enraf Nonius. This device revolutionised data collection methods, and cameras were soon to be found in almost all the protein crystallography laboratories throughout the world. Indeed, although film has since been replaced by electronic area detectors, the rotation method remains the standard procedure for macromolecular data collection. An international meeting on the use of the rotation method was organised by David Blow in 1975, and the proceedings were published in a monograph edited by Uli Arndt and Alan Wonacott (who jointly contributed 11 of the 17 chapters), which rapidly became a standard work.
In fact, the oscillation camera was only intended to be a short-term solution, as Uli's real ambition lay in developing a fully electronic area detector based on TV cameras. In the event, it was many years before this detector, the FAST, became commercially available, and the oscillation camera remained the workhorse in many laboratories until the late 1980s. By this time the FAST faced stiff competition from multiwire chambers, and subsequently from image plate detectors, and it never achieved the same level of popularity as its more humble pr edecessor. Despite the shortcomings of a relatively small active area, technical improvements to the original design (a double buffer) allowed it to collect oscillation data in a "shutterless" mode, a highly desirable feature that is still not possible with modern CCD detectors.
Although never attracted to working at large scale facilities such as synchrotrons (he was always much happier working with the LMB electronic and mechanical workshops), Uli was inevitably drawn into committees involved with the design of instrumentation for the new generation of X-ray sources. This led him to take a fresh look at focussing optics for use with laboratory sources. A literature search revealed a source of toroidal mirrors designed originally for X-ray astronomy, and theoretical calculations suggested that if these were combined with a very small focal spot size then it would be possible to obtain a brightness comparable with rotating anode generators from a sealed tube running at a fraction of the power.
By this time Uli had reached retirement age, but the microfocus system was his idea of an ideal retirement project. Together with Peter Duncumb and Jim Long, both experts in electron optics, and supported by grants from the Royal Society, Uli spent the next ten years bringing the project to fruition. The tube/mirror system was marketed by Bede Scientific Instruments, and performed remarkably well. It seems likely that his work in this area strongly influenced the development of microfocus sources by the much larger commercial X-ray equipment manufacturers, which have effectively replaced the more conventional designs that had remained almost unchanged for twenty years. Uli was not one to rest on his laurels, and was actively engaged on designing and fabricating improved mirror optics until a few weeks before his death.
Uli was very much a feature of life at the Laboratory of Molecular Biology. With his trademark bow tie and, until smoking was finally banned, his pipe, he was often to be seen in the canteen explaining his latest ideas on improving his designs, often with the aid of a picture scribbled on a paper napkin or an envelope. He was also an excellent story-teller, with a host of amusing anecdotes to hand. His autobiography entitled "Personal X-ray Reflections", soon to be published, is sure to provide entertaining insights into the life of one of the most influential figures in X-ray instrumentation.
Biographical Outline
Andrew Leslie, June 2006
This obituary was published in 'Crystallography News' no. 98 page 22 September 2006
See also obituary in The Independent, Saturday 8 April 2006.