Obituary

Bertram Neville Brockhouse (1918-2003)

[Brockhouse]

Taken from www.physics.mcmaster.ca/people/fs3_people_Brockhouse_BN.html
The following biography was prepared at the time of his retirement in 1984. It is taken from Physica 136B (1986) xxvii-xxxi (North-Holland, Amsterdam)

Bertram Neville Brockhouse was born July 15, 1918 in Lethbridge, Alberta. After graduating from high school in 1935, he obtained his Ph.D. from the U. of Toronto in 1950, with a thesis entitled 'The Effect of Stress and Temperature upon the Magnetic Properties of Ferromagnetic Materials'.

In July 1950 Brockhouse joined the staff of the Atomic Energy Project of the Nat'l Research Council of Canada at the Chalk River Nuclear Labs, northwest of Ottawa. His work at Chalk River involved studies of the resonant scattering of slow neutrons by strong absorbers such as cadmium and samarium. The measurements were made by placing the sample in a well shielded scattering chamber so that it was surrounded by an annular array of six Bismuth Fluoride detectors. The chamber was mounted on the arm of a single-axis spectrometer which had been built in the late nineteen-forties.

The idea of studying the inelastic scattering of slow neutrons occurred at a meeting Brockhouse attended in December 1950. It was soon decided that such experiments were feasible at the Chalk River reactor which was at the time, the world's highest flux beam reactor. The resonant scattering apparatus was used to study the energy distributions of initially monochromatic neutrons scattered by polycrystalline samples. The intensities of neutrons transmitted through various thicknesses of cadmium were compared with calculations based on ideal gas and Einstein models of the vibrational behaviour of the material.

Early in 1952 Brockhouse put together what he described as a 'large aperture double spectrometer', hoping to be able 'to measure the as yet unknown frequency distribution of normal modes' in a crystal. In 1953 he took advantage of an unexpected shutdown of the NRX reactor to spend ten months as the first foreign guest scientist in the Reactor Dept at Brookhaven National Lab. He worked on multiple scattering by flat specimens, magnetic scattering by zinc ferrite, powder magnetic diffraction studies of copper oxide, the development of improved monochromator crystals, and measurement of the incoherent cross sections of copper and gold.

On his return to Chalk River, Brockhouse again set up his crude triple-axis spectrometer, using a fixed angle monochromator facility with an aluminum crystal monochromator, a makeshift sample table, with the old single-axis instrument acting as the analysing spectrometer. The scattering angle at the sample position was fixed for a given set of measurements but could be changed by turning the sample table and moving the analysing spectrometer. The machine was used successfully for studies of the phonon frequency distribution of vanadium and the inelastic scattering by liquid lead and heavy water.

In the early months of 1955, 'preliminary measurements were made of energy distributions scattered by an aluminum single crystal in several different orientations'. This work led to the first successful determination of a phonon dispersion curve. It provided the first convincing demonstration of the power of the triple-axis method, at a time when groups at Saclay and Brookhaven were concentrating on a complementary time-of-flight technique.

Brockhouse next turned his attention to the possibility that neutrons might be used to investigate the 'thermal disturbances of the magnetized arrays of...coupled magnetic moments (which) can be described by means of quantized wave excitations called spin waves'. The ferrimagnetic material magnetite was chosen because large single crystals were available. The measurements of scattered neutron energy were carried out for 12 different orientations of the crystal, and it was concluded that the observed excitations were not phonons, but indeed 'in the spin system itself'. This was the first experimental determination of a magnon dispersion curve. These experiments were followed by extensive sets of measurements on a variety of crystals.

By the mid-fifties Brockhouse had begun to put together a beryllium filter-chopper spectrometer. The instrument was similar to the slow chopper at Brookhaven except that a filter difference technique was used to improve the overall energy resolution. Phonons in aluminum and beryllium were studied using the filter-chopper spectrometer, and an important series of measurements on water was completed.

A new type of high resolution time-of-flight instrument was devised by Brockhouse at about this time. This was the rotating crystal spectrometer, first mentioned in an AECL Physics Div. progress report in late 1957. This machine was installed at the NRX reactor, and an improved version, fitted with a cooled quartz filter, was later set up at the N5 hole of the new reactor NRU (Nat'l Research Universal).

The famous C5 triple-axis spectrometer, immortalised in Kittel's 'Introduction to Solid State Physics', was installed at the NRU reactor in 1958. This machine was an important training ground for many present day triple-axis spectrometrists. The first material to be studied using the C5 machine was a single crystal of silicon. Major improvements to the spectrometer were reported in 1959, including the construction of monochromating crystal control units with which 'it was possible to change the wavelength of the incoming neutrons automatically and continuously over a wide range'.

With the capability to vary the incident neutron energy of the C5 spectrometer, a new method for the study of high energy excitations became possible. This was the beryllium filter detector method, first tried at Chalk River in early 1960. Soon the N5 rotating crystal spectrometer was modified so that both the incident energy and the angle of scattering could be continuously varied.

During his highly productive years at Chalk River Brockhouse found time to take part in three Gilbert and Sullivan operettas, and a production of Shaw's 'Arms and the Man'. In 1962 Brockhouse moved to McMaster U. where remained until his retirement in 1984. At McMaster he took an active part in teaching, and was able to communicate his enthusiasm for physics to undergraduate and graduate students alike. He was influential in building up the department, and he and his graduate students built new spectrometers at the McMaster Nuclear Reactor, and later at the Chalk River NRU reactor.

Prof. Brockhouse received many honours over the years, including the Tory Medal of the Royal Society of Canada, the Buckley Prize of the American Physical Society, the Duddell Medal and Prize of the (British) Inst. of Physics and Physical Society 'for excellence in experimental physics', and the Centennial Medal of Canada. He received the Nobel Prize in 1994 for designing the Triple-Axis Neutron Spectroscope and his use of it to investigate Condensed Matter.

We owe a tremendous debt of gratitude to Bert Brockhouse. He has inspired many people to accept the challenges of neutron inelastic scattering, and to work long and hard to improve methods, materials and equipment in order to be able to do experiments properly and convincingly. Throughout his career he has demonstrated an honesty, thoroughness and scientific passion which are an example to us all. The 'absent-minded professor' stories are plentiful, and amusing, but the stories of his insistence on good experimental technique, and of his concern that time and money be efficiently used, are perhaps more to the point. His intuition, his dedication to research, and his kindness and concern for his fellow workers, are frequently mentioned by those who have had the pleasure to work with him.

John R.D. Copley, McMaster Nuclear Reactor, McMaster U., Canada

Footnote: Quotations in the text are taken from published papers and from progress reports of the National Research Council of Canada, Atomic Energy Project, and of Atomic Energy of Canada Limited, Chalk River Project. I am grateful to the many people who contributed information for this brief biography.