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New Scientist, 14 november 1992

Mark Oliphant dared to suggest that hydrogen could be an exploitable source of energy. Sixty years on, he is still enthusiastic about its potential.

David Ellyard

NOW in his 92nd year, Mark Oliphant is wearing well. His legs may no longer carry him with certainty; his hearing, impaired since childhood, may demand that conversations be carried at above normal volume. But he still stands tall. His ruddy face still routinely creases with mirth, aided by the booming laugh that has been his trademark for so long.

It is his mind that remains most active. Currently he is an evangelist for "hydrogen power", the use of hydrogen, released from water by electrolysis or some other process, as a fuel for vehicles or to power the innovative high-temperature fuel cells being developed in Australia. The electricity needed, he says, may well come from sunlight, captured by the high-efficiency solar cells developed by Martin Green at the University of New South Wales. Oliphant freely acknowledges the problems that remain, such as storage. Yet he feels able to say with conviction: "I am confident that such a system for producing power from hydrogen, the cleanest of fuels, will prove itself early in the next century".

His interest in hydrogen as a source of power is highly appropriate. His early scientific reputation was built on hydrogen or, to be precise, on pioneering researches he undertook into nuclear reactions involving deuterium, a heavy istotope of hydrogen. There is a key difference, of course. Today Oliphant sees hydrogen as a source of chemical energy liberated when hydrogen is burnt in an engine or a fuel cell. Such an energy source is within our grasp, with just some small matters of technology or economics to be tidied up. In the 1930s, the promise was something much more profound and much less accessible, energy from within the nuclei of hydrogen atoms.

The story begins in 1932 at the Cavendish Laboratory of the University of Cambridge. The Cavendish was then at the height of its influence. Ernest Rutherford, the New Zealand born physicist who had almost single-handedly created the science of nuclear physics, had built a team of researchers who led studies of the world within the atom. Some measure of the intellectual resources of the Cavendish comes form the annual photograph taken in 1932. Of the 30 or so staff and students gazing solemnly at the camera, nine were already, or were to become, winners of Nobel prizes. Oliphant stands in the second row of the group, fourth from the left and almost but not quite behind Rutherford. It is a symbolic position. Oliphant was not yet in the front rank of the Cavendish, but he was not far behind.

By the start of 1932, he had been at the Cavendish a little over four years. He had his doctorate and his first research papers in print. He was also growing close to Rutherford, professionally and personally. They were both antipodeans, given to plain talking. Oliphant and his wife Rosa were often guests of Ernest and Mary Rutherford at their holiday cottage in the north of Wales. And Rutherford appreciated Oliphant's growing reputation as a designer, builder and operator of the complex apparatus on which progress in nuclear physics was increasingly depending.

Arguably 1932 was the year of greatest achievement at the Cavendish with three discoveries of such importance that they truly deserve the overworked accolade "breakthrough". For the previous two decades, the standard model of the atom had contained two types of particles: the light, negatively charged electrons and lumps of positively charged matter called protons. Then in the space of a few months, the number of known fundamental particles doubled from two to four; the atoms of the lighter elements, far from being indivisible, were broken open at will; and powerful new machinery for both producing and detecting the particles came into use. These discoveries gave nuclear physics a new impulse. And the four men most closely involved at the Cavendish became Nobel laureates.

First to shine was James Chadwick, Rutherford's greatly respected second-in-command. At the beginning of 1932, he followed up an old idea of Rutherford's and some recent discoveries in France and Germany, and with brilliant insight identified a third fundamental particle- the neutron, close to the proton in mass but with no electrical charge.

John Cockcroft and Ernest Walton came next when, in April, they "split the atom". They had built one of the first particle accelerators, a sort of gun which used electrical potentials of several hundred thousand volts to send protons (the nuclei of hydrogen) speeding down an evacuated tube to collide with targets made of light elements such as boron and lithium. A multitude of tiny flashes on a screen covered with zinc sulphide revealed that, under proton bombardment, such light elements disintegrated into alpha particles, the nuclei of helium atoms.

Patrick Blackett completed the run of successes in August when he developed an improved version of the cloud chamber (another Cavendish invention) into a powerful research tool for revealing the paths of the particles in cosmic rays. With this, he trapped evidence of a new form of matter. This was the positron, identical to the electron except that it was positively charged; it was the first evidence of "antimatter".

Oliphant was only a spectator of these triumphs. His own research interests lay elsewhere. That was soon to change. Shortly after Cockcroft and Walton split the atom, the Rutherfords invited the Oliphants to their Welsh retreat. Conversation turned quickly to the recent breakthrough. Rutherford had never been overly keen on large and complex apparatus, fearful that building and running such machines might take precedence over what really mattered, the collection of experimental data. Yet he saw that times were changing and proposed a joint project that would explore where Crockcroft and Walton's work was pointing. The first task was to design and build an accelerator of the Crockcroft-Walton type, but with some new features.

Room with a past

Oliphant went to work in the summer of 1932 in a couple of low-ceilinged, stone flagged rooms in a historic precinct of the Cavendish basement. In one of the rooms, Lord Rayleigh, an early director of the Cavendish, had made the first precise measurements of the value of the ohm, the unit of electrical resistance. In the same room, Rutherford and Chadwick all but achieved the dream of the alchemists in 1919 when they transmuted matter for the first time, turning atoms of oxygen into nitrogen.

Oliphant's accelerator was as similar to Cockcroft and Walton's as a machine gun is to a cannon. Their accelerator produced a beam of very powerful protons, carrying up to 600 000 electronvolts of energy. Oliphant's machine yielded protons carrying at most 200 000 electronvolts, but delivered a hundred times as many protons to the target, so greatly increasing the chances of a nuclear reaction taking place. With counting chambers and electronic amplifiers replacing the eye and the sulphide screen, debris flying from the point of impact could be measured more precisely

Rutherford was very busy, with a laboratory to run and commitments that regularly took him out of town. This meant he kept his colleague on a very long leash, though the great man would drop in on Oliphant and his co-workers once or twice a day if he could, to see how things were going. He was intensely interested in progress, and his brilliant insights and explanations of observations were beyond price. But Oliphant really ran the show. His name was to come first on the half-dozen scientific papers hewn from the mountain of data yielded by the basement accelerator. Rutherford's name came last, if it appeared at all.

For the first few months, Oliphant and Rutherford used beams of protons to break open the nuclei of lithium, boron and beryllium, as Cockcroft and Walton had done, though with greater precision. By so doing they cleaned up many of the small uncertainties and turned out a paper or two.

The project took a leap forward in the summer of 1933, with a visit by Gilbert Lewis, a chemist from the University of California at Berkeley. Lewis had a present for Rutherford, a few drops of the newly isolated "heavy water". In this precious liquid, the hydrogen in many of the water molecules had been replaced by "heavy hydrogen", twice as heavy as the more common form. Although the Americans had already named the new form of hydrogen "deuterium", and its nucleus "deuton" (now changed to deuteron), Rutherford obstinately insisted on calling the atom "diplogen" and the nucleus "diplon". In the wake of Chadwick's discovery of the previous year, it was clear that each diplon contained a proton and a neutron. The diplons made most effective bullets for the Oliphant gun, producing many more transmutations than the single proton of a hydrogen nucleus.

Soon, however confusion set in. Oliphant tried a number of elements as targets, but the results all looked much the same. The debris clattering into the counting chamber was almost always dominated by protons with a constant energy-enough to travel 14 centimetres in air before coming to rest. There was some evidence that neutrons were present, although these were difficult to detect. Similar work was going on in Berkeley led by Ernest Lawrence, then a rising star in nuclear physics. The Berkeley researchers had an explanation, the deuton (sticking to their nomenclature) was an unstable particle which on impact with the target shattered into a proton and a neutron.

Sticking to the target

Not so, said Oliphant. He suspected that the answer lay with contamination of the target, because he had observed that the number of protons increased with time. If the diplons fired from the beam somehow stuck to the target, they would themselves become targets for more diplons coming behind. Oliphant (and Cockcroft, who was loading his accelerator with the same stuff), already knew that cleaning an exposed target greatly reduced the number of protons.

To settle the matter (and the well-mannered argument between Cambridge and Berkeley), Oliphant had a colleague make targets from ammonium sulphate and phosphoric acid, replacing some of the hydrogen in these compounds with heavy hydrogen. There was no doubt about the result. The characteristic pattern of protons appeared at once. Clearly the real collisions were between diplons, rather than between diplons and the original target material. Lawrence was quick to agree, with good grace, that Oliphant had been right.

The clash of the diplons still posed some puzzles. The matter become even more complex when Oliphant went hunting for any other particles that might be produced by the impact of diplon on diplon. His detection apparatus included a sheet of mica to determine the energy of particles leaving the site of collisions. These were of different thicknesses to represent the stopping power of various thicknesses of air. With the help of Rutherford's technical assistant George Crowe, Oliphant split a sheet of mica so thin that it showed dazzling interference colours. With that ultrathin film, they were able to observe a second group of particles, roughly equal in number to the protons, which only had enough energy to travel 1.6 centimetres through the air before coming to rest. These particles carried a single charge, and so were still hydrogen nuclei. But their tiny range indicated they must be heavy: the mass/energy calculations showed that they weighed three times as much as ordinary hydrogen. It could only be a hydrogen particle of mass 3.

The basement accelerator had delivered its first unique discovery Rutherford and Oliphant, claiming the right that falls to explorers of new territory called the particles tritons and the element tritium. The family of hydrogen nuclei, until recently consisting of one member, now had three members.

There remained yet another puzzle-that of the lone neutron. Clearly a pair of diplons contributed two protons and two neutrons to each interaction. For an instant, a particle with two protons and two neutrons must have existed, the result of the fusing of the two diplons. In the observed outcome, one proton emerged alone, and the other proton clumped with the two neutrons to make a triton. But there was also a neutron that emerged alone. Presumably this lonely neutron left behind two protons and the other neutron, hanging together in a particle with two units of charge and three units of mass-a helium nucleus of mass 3.

Discovery of a lifetime

It was the most important discovery of Oliphant's career. Of course the existence of helium-3 was not demonstrated, merely inferred, on the ground that it was the best explanation. The helium-3 left the target with such meagre energy-equivalent to a range of 0^.6 centimetres in air-that it defied detection for another two years.

It is not uncommon for major discoveries like these to develop a mythology that can obscure the historical details. Oliphant has for many years told a story about Rutherford and helium-3, an anecdote full of vivid detail. After many hours puzzling over the data, the story goes, Oliphant went home dispirited at the lack of progress. He was awoken in the small hours by a phone call from Rutherford, who boomed that he knew the identity of the short-range particles which had been seen. They were helium particles of mass 3. Oliphant, taken aback by the suggestion, gently asked what reasoning lay behind it. The phone shook as Rutherford roared back: "Reasons? Reasons, Oliphant? I don't need reasons. I feel it in my water!"

Of course the short-range helium particles of mass 3 had not yet been seen, but the facts do not really matter here. The story is more valuable for what it says about the Rutherford style, the way his mind worked and his impact on those around him. Such was the Rutherford spell that even Oliphant, who was now one of those closest to him , was loath to do anything of which Rutherford might disapprove.

Such caution caused Oliphant to wait until Rutherford was away before embarking on a secret investigation. Given that energy was released when diplons fused together, could more energy be extracted than was needed to bring the particles together, could such nuclear fusion be a net source of energy? With the help of Crowe, Oliphant lashed together equipment which fired a beam of accelerated diplons into a tube filled with heavy hydrogen gas. This pioneering experiment came nowhere near succeeding as there was far too little energy to begin with. But even the attempt was enough to arouse Rutherford's ire when he heard about it. Rutherford was adamant that atomic nuclei could never produce useful energy, calling the notion "moonshine". Within a decade he was to be proved wrong, with the first uranium fission reactor going critical in 1942.

In the case of hydrogen fusion, progress has been much slower, and useful power from fusion reactors is still decades away, if and when the day comes, Mark Oliphant will have a share in it, at least in spirit. It was he who first defined the vital reactions between deuterium particles, and first dared to suggest that those reactions offered a promise of power.

A life of building particle accelerators for others

MARK OLIPHANT was never again to be as productive in research as he had been in those few years at the Cavendish in the 1930s. Thereafter, he was to be a builder of particle accelerators for others to use.

His success with the deuterium reactions, combined with Rutherford's patronage, brought him recognition in the form of an FRS (he is one of the few to have been a fellow for more than half a century). In 1935 he took over Chadwick's old job as deputy director, and oversaw the construction of two more particle accelerators.

But he was now an attractive candidate for a "show of his own", and in 1937 the University of Birmingham offered him a chair in physics. It was a timely move for Oliphant. The influence of the Cavendish in nuclear physics was waning with the departure of Blackert, Chadwick and others, and Rutherford died around the time of Oliphant's departure. At Birmingham, he quickly secured a massive grant to build the biggest cyclotron in Europe.

The war years saw his influence grow though his ebullience and openness were seen by some as an inappropriate lack of discretion. The magnetron, which turned radar into a war-winning weapon for Britain, was invented and refined in his Birmingham laboratories. In spring 1940, he was able to bring the famous Frisch-Peierls memorandum to the attention of the authorities. Written by two German émigré physicists Otto Frisch and Rudolf Peierls, the memorandum told of the possibility of an atomic bomb, and stimulated the formation of the Maud committee and the quest for the atomic bomb.

Oliphant's friendship with Ernest Lawrence, begun in scholarly dissent, strengthened in the war years. In 1941, they shook the American scientific establishment out of its indifference to the military potential of the recent discoveries in nuclear physics. Once the Manhattan Project was under way Oliphant moved his team to Berkeley to work with Lawrence on the electromagnetic separation of the isotopes of uranium. After the war, shocked by the carnage of Hiroshima, Oliphant became an evangelist for the "peaceful atom", though his enthusiasm waned in later years.

In 1950, he returned to Australia to become the first director of the Research School of Physical Sciences at Canberra's Australian National University, which he helped to found. He was the only founding father to put his own career on the line by taking up a position at the university. The Canberra years mixed triumph with disappointment. Under his leadership, the school gained an international reputation. He was instrumental in setting up the Australian Academy of Science in 1954, and served as its first president. But his ambitious endeavour to build a massive synchrotron ended in failure. His critics dubbed it "the white Oliphant";

Oliphant retired in 1962, but in his early seventies he served five years as state governor of south Australia, bringing his own style to that office.

David Ellyard is a commentator on science and technology appearing on Australian radio and television. He is co-author with Stewart Cockburn of The Life and Times of Sir Mark Oliphant (Axiom Books, Adelaide, 1981).

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