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Professor John Newton was interviewed in 2010 for the Interviews with Australian scientists series. By viewing the interviews in this series, or reading the transcripts and extracts, your students can begin to appreciate Australia's contribution to the growth of scientific knowledge.
The following summary of Newton’s career sets the context for the extract chosen for these teachers notes. The extract describes the challenges of using an early particle accelerator and Newton’s PhD work in measuring gamma rays. Use the focus questions that accompany the extract to promote discussion among your students.
John Oswald Newton was born in 1924 in Birmingham, England. He won a scholarship to St Catharine’s College, Cambridge, where he completed the first two years of his bachelors degree (BA, 1944) before joining the war effort in 1943. During WWII Newton worked as a junior scientific officer at the radar facility in Malvern. In 1946, he was able to return to the Cavendish laboratory at Cambridge to finish his MA (1948) and later his PhD (1953). Newton’s research during this time looked at the simultaneous emission of protons and gamma rays when elements are bombarded with deuteron (heavy hydrogen nucleus containing one proton and one neutron).
Newton joined the Atomic Energy Research Establishment (AERE) in Harwell in 1951. He began as a fellow before promotion to principal scientific officer in 1954. Whilst at Harwell he researched very heavy nuclei by Coulomb excitation with alpha particle beams. Newton then accepted an appointment as senior lecturer (1959-67) and later, reader in physics (1967-70) at the University of Manchester. Here he investigated the transition of excited states in carbon and nitrogen, along with continuing to develop experimental apparatus and electronics. The first of Newton’s visits to the Lawrence Radiation Laboratory (LBL) in Berkeley, USA took place in 1956-58. He made subsequent visits in 1965-67, 1975 and 1980-81. These fruitful trips resulted in significant developments in the fields of double-Coulomb excitation, continuum gamma rays and the investigation of nuclear structure through statistical gamma ray decay.
In 1970, Newton left England and became professor of nuclear physics and head of department at the Australian National University (ANU), Canberra. Newton was instrumental in the installation of a new accelerator at the ANU and introduced a new collaborative research ethos to the department. He was made emeritus professor in 1990 and continued as a visiting fellow in the Department of Nuclear Physics until 2008.
Professor Newton was awarded the centenary medal in 2001 and elected a Fellow of the Australian Academy of Science in 1975.
Life at the Cavendish
Who was the Head of the Cavendish at the time?
The Head of the Cavendish was Lawrence Bragg. He got a Nobel Prize for his work on the famous Bragg scattering law for X-rays. He very rarely spoke to research students; I think he felt that they were rather beneath him. But one day we heard a lecture by Cecil Powell, who had sent up photographic plates on a balloon to look at cosmic rays and discovered the pi-meson; it was a very simple experiment, of course. That inspired Bragg so much—because he liked such things—that he actually spoke to me when we were collecting our bicycles from the basement. He said to me, ‘I really think the days of these big machines are over now.’ I wonder what he would think of the Large Hadron Collider?
Who was your PhD supervisor?
At the Cavendish in those days, one had little interaction with one’s supervisor. He would suggest a problem on which to work but after that, a brief talk once a month or so would be the most one could expect. This system was excellent for the best students, fostering initiative and self-reliance, but could be disastrous for weaker students.
My PhD supervisor was Bill Burcham. He was in charge of an accelerator that reached up to about one million volts on its terminal, if you were lucky. This was the accelerator that I used. It was a development of the original Cockcroft-Walton machine. The impressive accelerator-hall had to be very big to minimise the chance of sparking to the walls or ceiling.
Was it open to the room?
Yes it was. Going into the accelerator-hall, when the high voltage was on, was very exciting; your hair literally stood on end. Often you would hear an enormous bang and see a brilliant flash. The accelerator was actually very primitive. Its voltage stability was very poor and the energy of the beam was spread over a range of plus or minus 30 keV. It had a very poor vacuum as well. You have to accelerate the ions in a vacuum; otherwise, they just lose all their energy in the air. The vacuum was full of oil vapour from the un-baffled oil-diffusion pumps. When the beam hit the target—which you hoped was very clean—it cracked the oil-vapour and produced a layer of carbon on it. Sometimes, these layers would get so thick that pieces fell off!
Probably most of the reactions were on the carbon rather than on the target.
Yes, that could be the case.
So the contrast with equipment today or even 20 years ago must have been something dramatic.
Oh, it really was incredible. In those days there were no electronic calculators, no computers, and no transistors. The electronics used valves, which were large and used a lot of power. The equipment was all large and heavy and it wasn’t very reliable. For instance, when we had to count pulses from detectors using a scaler, we usually put three scalers in parallel; if two of them gave the same result, we would assume that was the correct result. This is something that people these days wouldn’t think of. In fact, we had to make most of our electronics anyway, as there were only a few things that we could buy commercially. Most calculations were done with slide-rules and with pen and paper. Another hazard on winter afternoons was that the nominal supply voltage of 210 (50 Hz), would drop as low as 170 volts, making our electronics unusable. We had to raise it back to 210 volts with a manually operated variac. At 5 p.m., when the shops shut, the supply would shoot back up to 210 volts within a few minutes. Failure to quickly wind down the variac would overheat some components, causing damage and malfunction and a strong smell of selenium.
PhD research – measuring gamma rays
What did you actually work on in terms of the physics?
The accelerator had a low voltage, so we could only study light elements; there wasn’t enough energy to cause reactions in heavier ones. I studied mainly energy- states in light nuclei. Part of my thesis project was to measure gamma-rays in time- coincidence with particles from deuteron-induced reactions and try to learn about the energy levels from which the gamma-rays came. Unfortunately, when you bombard something with deuterons, it doesn’t produce just the reaction that you want; it produces many other reactions as well. So this gives a vast counting rate in your detectors. If you want to successfully measure time- coincidences between the particles and gamma-rays of interest, you really need a very short resolving time. At that time, a resolving time of about one microsecond, possible with available electronics of the radar period, was completely inadequate for this task. So I had to develop equipment that would enable me to produce nanosecond resolving times.
That is 1,000 times shorter.
Yes. Actually, I only managed to get 100 times shorter, but that was good enough; at that time, it was quite an achievement. I had to make instruments and equipment such as amplifiers, double-pulse generators, etc. I also had to make detectors that would produce fast pulses. It’s no use having fast electronics if the pulse from the detector rises very slowly. So I had to make scintillation detectors for both particles and gamma-rays. All this was a big challenge, which took a lot of time, but I succeeded by my own efforts.
And you got some good results?
Yes, I did. I bombarded lithium-6 with deuterons and was able to establish that the first excited state in lithium-7 had a spin or angular momentum of one half. With another proton-induced reaction, I measured the polarisation of the 6.1 MeV gamma-rays from the first excited state of oxygen-16 and showed that it had negative parity. At that time this was the highest energy gamma-ray whose polarisation had been measured, and this remained true for very many years afterwards.
An edited transcript of the full interview can be found at http://www.science.org.au/scientists/interviews/n/jn.htm.
Focus questions
Select activities that are most appropriate for your lesson plan or add your own. You can also encourage students to identify key issues in the preceding extract and devise their own questions or topics for discussion.
For some basic information, students can start here:
accelerator
decay
deuteron
energy level
gamma ray
nucleus
particle
radiation
vacuum
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