From Wartime Radar to W-Bosons: The Experimental Physics of Joan Freeman.

In 1983, one of the great pillars of modern physics was cemented in place when CERN announced the discovery of a group of particles that stood at the center of the attempt to unify two of the universe's fundamental forces: electromagnetism (which explains how moving charges give rise to, and interact with, electrical and magnetic fields) and the weak force (which allows atoms to change their identity without changing their mass).  It was an exciting moment of great potential - with electromagnetism and the weak force unified, surely it wouldn't be that long before all forces could be explained as aspects of one single, overarching phenomenon.

Credit for that moment went out to the originators of the theory of electroweak interaction, who had already won the Nobel Prize in 1979 for their effort, and to the teams at CERN whose efforts uncovered the existence of the W and Z bosons which the electroweak theory predicted must exist, but lost in the excitement of the moment was the contribution of an experimental physicist whose work in the 1960s and early 1970s provided crucial data for the plausibility of electroweak theory, Australian born Joan Freeman (1918-1998).  

Her career spanned three continents and two wildly different fields of physics, but 

because she was the sort of scientist who designed and carried out experiments rather than the sort who postulated new theories, her story has been wrapped in the obscurity that tends to be the fate of most experimental scientists in the modern age.  Getting one's hands dirty, constructing precise measurement devices out of tubes and wire and primal engineering know-how, makes a great scene in an Iron Man movie, but when it comes to the history books, the detailed technical jargon of the practical engineer tends to pale in interest and representation before the seductive large scale theories of a Weinberg or a Hawking.  

So, let's spend some real time with Dr. Freeman, amidst the lathes and sealing wax, to see how much a passion for physics and a brilliance for experimental design can accomplish when given encouragement and recognition.  Freeman was the granddaughter of an Australian gold miner who had won and lost a fortune in speculation.  His hard times coincided with the moment when his gifted daughter, Freeman's mother, was due to enter college.  A masterful pianist, she had to forego her education because of the family's suddenly straitened circumstances, and when she had a daughter of her own, she swore that no privation would be too great if it allowed her own daughter to have the education that she was denied.

Privation was, indeed, the watchword for Freeman's youth.  In the years of the worldwide Depression, her father lost his job and eventually left the family, leaving her mother as the family's primary breadwinner.  She ran and managed a small school for girls where she taught all the classes.  Her teaching was popular, but the premises, a run down house with a primitive outdoor restroom, placed a limit on her ability to expand, so the family revenue was always just barely poking its nose above the swirling waters of insolvency.  While her mother worked a relentless schedule to keep her school afloat, Joan was fulfilling every bit of the maternal expectations placed upon her by exceeding in her own school studies.  When finances proved too tight to pay for another year at the private school that her mother insisted on, Freeman's principle offered to waive tuition on the strength of her scholastic efforts, feeling that her performance on the upcoming national exams would spread the fame of the school.  By considering the scholarship an investment on the school's part rather than an act of charity, the Freemans were convinced into accepting the offer, and Joan's education continued at its frantic pace.

The problem was, however, that the science offerings at her school were insufficient preparation for the national exams, and certainly did not meet up to the level of Freeman's curiosity.  One of her treasured childhood memories was that of poring over the set of children's encyclopedias she had been bought and performing all the scientific experiments suggested therein, either by herself, or with any boys in the neighborhood who were up for collaboration.  She was a natural experimenter, a born builder (she hounded her parents incessantly for a Meccano set after seeing a neighbor child with one and proceeded to build all manner of devices and vehicles), but that instinct got precious little encouragement in the girls' school setting of the time, so she and her mother hatched a plan.

They traveled to the Sydney Technical College, where science classes and labs were offered to aspiring engineers and workers seeking to improve their situation.  They presented themselves to the chemistry department, asking to be admitted to courses there, but the department head curtly dismissed them without a second thought.  Unperturbed, Freeman's mother marched them to the physics department to try again, where the lead lecturer, GH Godfrey, happily admitted Freeman to his evening courses on the condition that her presence was kept a secret from the administration.  

Here at STC she took her first real science classes, and discovered what it meant to work under real laboratory conditions.  In spite of being the youngest in the class, and having to miss several lectures because of the exam schedule at her regular school, she managed to come in first in the course exams and later, when taking the national exams that would qualify her for a much needed college scholarship, she won not only the Fairfax Prize for General Proficiency Amongst Female Candidates, but the James Aitken Scholarship for General Proficiency.  Armed with this financial support, she entered Sydney University in 1936.

In her third year of college, one of her professors, V A Bailey, recommended that his students research magnetrons over the summer and write up a research report about what they found.  Magnetrons were at the time a new technology for producing high frequency oscillations in the microwave spectrum with a limited presence in the scientific literature.  Most students decided to put off the project until just before returning for the fall season, but Freeman dove into the research, producing a write-up of current knowledge and a full bibliography of available articles on the subject.  Bailey was impressed by her initiative and thoroughness, and when it came time to hand out senior projects, he gave her the one most closely aligned with his own research: creating ultra-high electrical discharges in gases in order to probe the physical characteristics of the Earth's ionosphere.  

She achieved success in producing resonance effects across a variety of gases, which inspired Bailey in turn to entrust her with an upcoming talk about yet another brand new piece of technology: klystron oscillators.  These had been invented in the United States just the year before, and allowed the production of much higher power microwave radiation than that of the early magnetrons.  She had never seen such a device, and didn't know anybody who had, but managed to give the required talk which happened to be attended by one Dr. Joseph Pawsey, the head of the Radiophysics Laboratory (RP) at the Council for Scientific and Industrial Research, which would assume a central role in developing radar technology in the coming war against Japan.

In 1941 Freeman saw that a position was available at RP for somebody with experience in high-frequency oscillation, the very field she had been researching for the last three years.  She applied for the job and was quickly admitted as a research officer.  Shortly after she arrived, Ruby Payne-Scott took up a position at RP as well, but whereas Payne-Scott achieved a moment of glory as a pioneering radio astronomer before having her career suddenly dashed by the discovery of her secret marriage, Freeman worked steadily away at developing the klystron oscillator that would be at the heart of a microwave-range radar defense system for Australia.  She designed the oscillator and it was humming along perfectly when it was discovered that a more stable power source would be necessary to make the radar effective, and Pawsey turned once more to Freeman to design it in spite of the fact that she had never worked on such an electrical engineering project before.  

She threw herself into the task and successfully designed the required high stability power source, as well as the switch that allows for a single radar aerial to be used as both a transmitter and receiver of signals.  The final radar assembly exceeded expectations and Freeman was immediately set the task of designing the transmit/receive switch for a new radar system that would have been optimum for detecting aircraft at multiple altitudes.  It was a complicated device striking into new territory, but she and the RP team succeeded again, though the end of the war in 1945 meant the new system was never actively put into use.  

With the war over, and the resultant decline in need for intensive development of new radar systems, Freeman had a chance to survey the direction of her life and determine what she truly wanted to research.  In 1946, her superiors told her that they had selected her to apply for a prestigious opportunity to study at whatever university in England she might choose.  She applied, and was one of two RP researchers chosen for the program, which forced the question of what she truly wanted to study, and where.  She loved the results coming out of research into the structure of the nucleus, but had been warned that it was difficult for women to find permanent work in that field.  Undaunted, she decided to apply to the Cavendish, that Mecca of early 20th century nuclear research, and was accepted for the Fall 1946 term.  

The Cavendish that Freeman arrived at in October, however, was not what it had once been.  From 1871 to 1937, the Cavendish Laboratory featured a string of world renowned scientists at the helm who wrested the secrets of the atom from a jealous Nature: James Clerk Maxwell, Lord Rayleigh, J.J. Thomson, and Ernest Rutherford formed an unbeatable progression whose discoveries are now the stuff of every chemistry and physics textbook.  Rutherford, however, died in 1937 and with the arrival of World War II the venerable lab saw its best and brightest distributed amongst various war projects, most never to return.  The post-war Cavendish, then, was coasting rudderless, overstuffed with new researchers who had neither dedicated advisors nor well-defined projects to work on.  Freeman was in danger of sliding into oblivion when she took the reins of her fate in her own hands and decided that she would, by pure force of will, nudge her way into research of importance.  She worked with whatever experimentalists would show her new techniques for the construction of nuclear-probing apparatuses, and did a deep dive into the research of the professor who determined access to the laboratory's HT1 particle accelerator, W E Burcham.

She discovered that Burcham had been carrying out experiments about the production of short-range alpha particles (particles comprised of two neutrons and two protons) from nuclei that had been bombarded by neutrons, but had not had a chance to deepen his investigations because of the onset of the war.  She decided to approach him with the idea of continuing his original research and to her great joy she found that the man who had said he had no room for any more graduate students was only too willing to make room for one who seemed so eager to carry on with research he had been compelled to abandon.  She had gained for herself an advisor, and access to a powerful accelerator to do original research on nuclear processes.  

Throughout the late 1940s she produced a stream of useful results about the behavior of light nuclei under bombardment by protons and neutrons, and in 1949 passed her PhD oral exam on the strength of her research of short-range alpha particle ejection.  By 1950, however, most of those who had arrived as research students to study nuclear physics at the Cavendish had left, and the laboratory was showing signs of moving in new directions entirely, and so when a recruiter from Harwell (a research center dedicated to atomic investigation) approached her that year with an offer to do fundamental research at their cutting edge facilities, she leapt at the opportunity, joining Harwell in 1951.

It was here at Harwell that she made her name as a researcher lending experimental heft to cutting edge physical theories. In the early Fifties she carried out research that invented new ways of studying nuclear excited states which in turn produced data that was valuable to the development of the nuclear shell model.  Then, in the late Fifties she formed an important alliance with physicist Roger Blin-Stoyle to investigate new theories about beta decay (the phenomenon whereby a nuclear proton changes into a neutron or vice versa) being promulgated by Richard Feynman and Murray Gell-Mann.  To support this theory required precise measurement of energies produced during the beta decay of particular isotopes.  In particular, a measurement of Aluminum-26's energy and half life would go far to backing the Feynman-Gell-Mann model, and Freeman believed she could produce aluminum-26 by proton bombardment of magnesium-26.  Blin-Stoyle was impressed with her results and wanted her to explore further the existing models of beta decay.  She ultimately investigated ten different isotopes, providing crucial data for the emerging field of beta decay study.

The data she produced in these studies would go on to play a largely unsung role in the establishment of electroweak theory in the early 1970s.  According to this theory, at high enough temperatures (like those of the early universe), electromagnetism and the weak force (which is responsible for beta decay) were one unified phenomenon, only splitting into different forces with the expansion and subsequent cooling of the universe.  Weinberg and Salam hypothesized a model that harnessed Gell-Mann's quark theory to explain the changing of a neutron to a proton through the mediation of a new massive particle called a W boson.  That particle would not be physically discovered until 1983, but in 1970 Blin-Stoyle took Freeman's data and used it to demonstrate that the beta decay reaction, as observed throughout the late Fifties and early Sixties by Freeman, could only be explained by the existence of a heavy W boson.  It was an important paper that was built upon in 1975 by another researcher who showed that the experimental data was also compatible with the Z boson posited by Weinberg and Salam and which would also not be discovered until 1983.  

The work of Joan Freeman, then, formed an important part of the evidential foundation for theoretical probing of the electroweak theory during that long decade and a half that lacked accelerators powerful enough to directly confirm it.  And yet it is a rare source indeed that mentions the role her early experiments played.  For her part in the development of beta decay theory she was jointly awarded, with Blin-Stoyle, the Rutherford Medal of 1976, becoming thereby the first woman to receive the prestigious award for contributions to nuclear physics.  Her beta decay group folded in 1977, having accomplished all it could have reasonably been expected to with the equipment at its disposal, and in 1978 she was placed on mandatory retirement, but given a five year consultancy to do more or less whatever research she wanted without any administrative entanglements.  After years of fighting to keep alive the tandem accelerator group she had led since 1960, she was happy to be free of the headaches of funding and organizational meetings, and enjoyed semi retirement with her husband John Jelley and their late-life discovery of the charms of sailing.  John fell ill in 1995, and Freeman's life thereafter revolved around a valorous but doomed attempt to nurse him back to health.  He died in 1997, just shy of their fortieth anniversary, and she followed him the year after.  

FURTHER READING:  

I first came across Joan Freeman as a figure in the shadows of books about two other famous women scientists: the radio astronomer Ruby Payne-Scott, and the experimental physicist Chien Shiung Wu, whose experiments in parity breaking put Feynman down the road to the beta decay theory which Freeman would experimentally investigate.  And that's where she would largely have remained had she not taken it upon herself to write the story of her own life in A Passion for Physics: The Story of a Woman Physicist (1991), thereby once again demonstrating how critical it is for women scientists to tell their stories lest they be claimed by the historical shadows.  It's a wonderful memoir full of pluck and initiative and a genuine joy at finding out the universe's building blocks, and a definite must for the bookshelf.