Obituary - Bertram Neville Brockhouse (1918 – 2003)

Bertram Neville Brockhouse (1918 - 2003)

Brockhouse

On an ordinary Wednesday morning in October 1994 Bert Brockhouse got out of bed at his usual time—about 6:45. As he stretched a bit to loosen the overnight aches of his 76-year-old body, he saw the little red light blinking on the answering machine.

Who could have called in the middle of the night? he wondered, as he pressed the play button. He listened to a voice announcing that it was from Stockholm: “B. N. Brockhouse and C. G. Shull have been selected as recipients of the 1994 Nobel prize for physics.” Brockhouse was stunned. For a moment he thought, Oh that’s interesting, but then he realized, I am B. N. Brockhouse, and he called his wife Dorie, to listen to the tape again with him.

The next year was one of travel, awards, banquets, and lectures. Brockhouse was simply beamed out of quiet retirement. In his annual Christmas letter to friends that year, after describing all the festivities in Stockholm, Brockhouse said, “If anyone cares, we got a new car in the summer, a Chrysler Neon.”

The origins of Brockhouse’s Nobel Prize could be traced back to 1951. Fresh out of the University of Toronto with a PhD in Physics, Brockhouse sat at his desk in a faded blue-shingled wartime hut at Chalk River, Ontario, home of Canada’s Atomic Energy Project funded by the National Research Council.

He gazed out the window at the snow. It was winter, but he felt warm inside the hut. He just sat there thinking, mull- ing things over in his mind. The other night he had been at the home of Donald Hurst, his boss and head of the Neutron Spectrometer section. They had been reading a 1944 paper about neutrons— subatomic particles with no electric charge that, together with protons, make up the nucleus of an atom. The existence of neutrons had only been verified about 12 years before. Not much was known about them. Brockhouse didn’t quite understand the theories in the paper, but he felt it had a lot of interesting ideas. He was supposed to be working on something else, but he couldn’t stop thinking about the concepts in the paper and how he could do experiments at Chalk River to try out some of the new theories.

He fiddled with some math on his notepad for a while and then went to the coffee room. As he passed the lab that housed the radioactive nuclear pile, a controlled nuclear reaction that emitted one of the most powerful sources of neutrons in the world at the time, he wondered whether he could put it to use. In the coffee room he met Hurst. Brockhouse went up to the blackboard and said, “Don, there’s something I’d like to show you.” He sketched out some equations on the blackboard. The math described a device they could build that would use a neutron beam as a better type of spectrometer, a kind of flashlight that could probe into the mysteries of crystal structures and other solids such as metals, minerals, gems, and rocks.

In the 1920s Bert Brockhouse’s family moved to Vancouver. After high school, instead of going to university, Brockhouse worked as a radio repairman. Then World War II came along and he used his radio skills as an electronics technician in the Canadian Naval Reserve. When the war ended, Brockhouse went to the University of British Columbia, majoring in Math and Physics. After marrying Dorris Miller, a film cutter at the National Film Board, Brockhouse finished his PhD and the newlyweds moved to Chalk River.

( Extracted, with permission, from www.science.ca/scientists/scientistprofile.php?pID=4 )

In July 1950 Brockhouse joined the staff of the Atomic Energy Project of the National Research Council of Canada, later to become Atomic Energy of Canada Limited (AECL), at the Chalk River Nuclear Laboratories about 130 miles northwest of Ottawa.

In the early months of 1952 Brockhouse put together what he described as a “large aperture double spectrometer”, in reality a triple-axis machine, hoping to be able “to measure the as yet unknown frequency distribution of normal modes” in a crystal. Much effort was put into trying to get the machine to work, including attempts to produce monochromator crystals with higher reflectivity, and improvements to the shielding, but by the end of the year the spectrometer was not producing results.

In 1953 Brockhouse took advantage of an unexpected shut- down of the NRX reactor to spend ten months as the first foreign guest scientist in the Reactor Department at Brookhaven National Laboratory. On his return to Chalk River, Brockhouse again set up his crude triple-axis spectrometer, using a fixed angle mono- chromator facility with an aluminum crystal monochromator, a makeshift sample table, and the old single-axis instrument acting as the analysing spectrometer. The scattering angle at the sample position was fixed for a give set of measurements but could be changed by turning the sample table and moving the analysing spectrometer on a set of rails. The machine was used success- fully, thanks in large part to its improved monochromator, for studies of the phonon frequency distribution of vanadium and of the inelastic scattering by liquid lead and light and heavy water: these measurements were reported at the January 1955 meeting of the American Physical Society in New York City. The energy dependence of the paramagnetic scattering by materials such as the manganese oxides was also studied.

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, in collaboration with A.T. Stewart, 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 at Brookhaven were concentrating their attention 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, for the very good reason that large single crystals were available. The measurements of scattered neutron energy were carried out for 12 different orientations of the crystal, using 1.52 Angstroms incident neutrons and a scattering angle of 18 degrees, 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.

A new type of high resolution time-of-flight instrument was devised by Brockhouse at about this time, following a conversation with D.G. Hurst. This was the rotating crystal spectrometer, first mentioned in an AECL Physics Division progress report in late 1957. The first version of this machine was installed at the NRX reactor, and an improved version, fitted with a cooled quartz filter and initially located at the NRX reactor, was later set up at the N5 hole of the new reactor NRU (National Research Universal). R.N. Sinclair, who had worked with Brockhouse as a postdoctorate fellow, built a similar machine at Harwell on his return from Chalk River.

The rotating crystal spectrometer was initially used for a detailed study of the quasi-elastic component of the scattering by water. The results were consistent with earlier Chalk River results, and strongly suggested that the supposed fine structure in the data of D.J. Hughes and his collaborators was spurious. The spectrometer was also used for an extensive series of experiments, by D.G. Henshaw, on liquid helium: the first inelastic work on helium at Chalk River had been undertaken using the filter-chopper spectrometer. Other early work using the rotating crystal spectrometer included phonon measurements on lead and sodium iodide.

The famous C5 triple-axis spectrometer, immortalized in Kittel’s “Introduction to Solid State Physics”, was installed at the NRU reactor in 1958. This machine remained in use for more than twenty years and 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; lead was also studied, supplementing the earlier work on the rotating crystal spectrometer.

With the capability to vary the incident neutron energy of the C5 spectrometer, a new method for the study of high energy ex- citations became possible. This was the beryllium filter detector method, which was first tried at Chalk River in early 1960. At about this time the N5 rotating crystal spectrometer was modi- fied so that both the incident energy and the angle of scattering could be continuously varied.

In 1962 Brockhouse moved to McMaster University where he was a professor of Physics 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 received many honors over the years, including the Tory Medal (Royal Society of Canada), the Buckley Prize (American Physical Soc.), 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 was a Foreign member of the Royal Swedish Academy of Sciences.

We owe a tremendous debt of gratitude to Bert Brockhouse. He 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 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, dedication to research, and kindness and concern for his fellow workers, were frequently mentioned by those who had the pleasure to work with him.

(Extracted, with permission, from https://www.physics.mcmaster.ca/research/bertram-n-brockhouse.html)