Australasian Science Magazine

Dr Neville (“Nod”) Parsons in retirement.

By Paul J Edwards

The death in Hobart on 30 December 2017 of 91-year-old Antarctic physicist and expeditioner Dr Neville (Nod) Parsons marks the end of an era of Australian Antarctic research and exploration.

Not many physicists have lent their names to a mountain as did Parsons to a “huge, sheer-sided” peak at the northern end of the David Range in Australian Antarctic Territory. This followed the first exploration of the David, Casey and Masson ranges in January 1956 by an Australian National Antarctic Research Expedition party of five led from Mawson by Antarctic explorer John Béchervaise over heavily crevassed ice. Béchervaise and Neville "Nod" Parsons were subsequently awarded Imperial Polar Medals for their work.

Dr Nod Parsons and Dr Geoff Fenton were the founding members of a joint University of Tasmania / Australian Antarctic Division (AAD) cosmic ray research team formed in Hobart in the early fifties when the University of Melbourne gave up cosmic ray research in favour of nuclear physics.

Although Parsons himself moved to the University of Calgary in 1964, the Hobart based group and its graduates helped clarify the influence of the sun on galactic cosmic rays in the vicinity of the earth for over a period of more than six decades. The group focussed on the role of the IMF, the interplanetary magnetic field, and the “solar wind” in mediating the influence of the sun through a study of solar-related cosmic ray intensity fluctuations.

Because primary cosmic rays are electrically charged nuclei, mainly hydrogen, the most abundant element in the universe, they are deflected by solar and terrestrial magnetic fields, despite having been accelerated to very high energies elsewhere. They are most intense at high latitudes, in Arctic and Antarctic regions, and least intense at the equator where the barrier presented by the earth’s magnetic field is highest.

As the primary cosmic ray nuclei strike the atmosphere they generate a cascade of secondary cosmic ray particles that can be detected and counted at sea level. Historically, knowledge about the primary cosmic radiation was inferred from measurements on this secondary radiation, despite limitations imposed by the earth’s magnetic field and atmosphere and by variations in the IMF over the 11 year solar sunspot cycle.

The Hobart group initially established secondary cosmic ray observatories at sea level in the Antarctic to study cosmic ray intensity variations and their directional characteristics. Parsons himself installed meson telescopes on Macquarie Island in 1950 and directed the Antarctic program thereafter. He installed two large telescopes himself at Mawson on the Antarctic mainland in 1955. The group established a network of observatories in Antarctica, Australia and New Guinea, contributing to internationally coordinated research during and after the IGY (the International Geophysical Year) of 1957/8. Monitors were also placed underground to extend the measurements to greater energies and at mountain and balloon altitudes to study lower energy radiation generated in solar flares and in terrestrial auroras.

An unexpected early outcome of the balloon program was the detection in 1962 of radioactive fission products over Hobart. These were believed to be transported south following a breach of the earth’s magnetic field by high temperature plasma ejected from the high altitude northern hemisphere thermonuclear explosion Starfish Prime.

Before moving to Canada Parsons returned to Macquarie Island in the early 1960s to monitor auroral x-rays with balloon-borne detectors in a productive collaborative research program with the University of California. He later developed an active ground-based auroral research program at the University of Calgary.

After his departure the management of the AAD side of the research collaboration with the University of Tasmania passed to Dr R M (Bob) Jacklyn AM and then to Dr Marc Duldig. Dr AG (Geoff) Fenton AM, the founding father of the group, managed the university side for a further two decades.

Research on the solar modulation of cosmic rays continued as part of an international program of observations including in-situ measurements of primary cosmic rays in interplanetary space by Hobart graduate Professor Ken McCracken at the University of Texas at Dallas with the Pioneer and IMP series of spacecraft (https://tinyurl.com/yd6pcpkz).

Parsons and McCracken had earlier analysed the time delays to the onset of a transient decrease in cosmic ray intensity observed at a number of southern observatories during the IGY. They discovered the strong directional character of the cosmic ray flux during the course of such events. McCracken later pioneered novel computer techniques to show that event onset times observed at different longitudes on the earth’s surface were consistent with the Parker model of the interplanetary magnetic field. This was the first observational confirmation of the model.

Parker had proposed that magnetic field lines diverged from the sun in in the form of an Archimedes spiral due to the combined effects of the rotation of the sun’s surface and the outward radial flow of the solar wind, rather like a rotating garden hose sprinkler. Near the earth, the arms of the spiral are inclined at a fixed angle to a line drawn from the earth to the sun. This introduces a longitude dependence to the onset times as the earth rotates and progressively points the various telescopes in that direction.

Parsons left cosmic ray research and began a distinguished career as a teacher and academic administrator at the University of Alberta in 1964, at the beginning of the IQSY, the International Quiet Solar Year, an internationally coordinated investigation of solar related phenomena at a time of minimum solar activity. He later returned to Australia as director the North Brisbane College of Advanced Education before finally retiring as director of the Brisbane CAE complex, amalgamated in the Dawkins higher education reforms of the late 1980s.

Since that time observations of short term fluctuations associated with magnetic storms and solar flares, together with the variation in cosmic ray intensity with solar activity over the 11 year sunspot cycle, have become useful tools in space weather forecasting. The analysis of cosmic ray-generated (“cosmogenic”) radioactive nuclides such as carbon 14 in organic material and beryllium 10 in polar ice cores for dating has added utility to the once purely academic study of galactic cosmic rays.

Not only are these cosmogenic radio nuclides useful for dating purposes but they also provide a measure of the cosmic ray flux, and hence of solar activity extending thousands of years back to the last glacial epoch. Such paleo-cosmic ray analyses suggest a relation between solar activity and climate, periods of low activity being associated with lower global temperatures (https://doi.org/10.1063/1.4792558), and are evidently relevant to current environmental concern with climate change.

Nod Parsons welcomed these practical applications of cosmic ray research. Coming from a religious and scholarly family background, he was a firm believer in 17th century philosopher Francis Bacon’s words “science discovery should be driven not just by the quest for intellectual enlightenment….but for the glory of the Creator and the relief of man’s estate.” His passing was marked by the lowering of the Canadian flag at the University of Calgary.