Professor Perkowitz Reveals Scientific Legacy Of The Nuclear Physicist

Sidney Perkowitz uncovers the scientific legacy of the nuclear physicist, who overcame great adversity to become a renowned researcher and advocate for women in science.

Professor Perkowitz Reveals Scientific Legacy Of The Nuclear Physicist

Sidney Perkowitz uncovers the scientific legacy of the nuclear physicist, who overcame great adversity to become a renowned researcher and advocate for women in science.

Some people know from a young age that they want to be a scientist and that – with enough ability and effort – they can reach that goal. Gertrude Scharff (Scharff-Goldhaber after she married) felt that early calling. And while she had the ability to fulfil it, her path to scientific success had more than its share of personal hardships and professional obstacles.

Born to a German-Jewish family on 14 July 1911, she lived through the First World War, the post-war upheavals in Germany and the rise of Hitler. After earning her PhD in physics from the University of Munich, she sought entry into a profession dominated by men. When she fled Nazism, she faced difficulties as an immigrant to the UK. And when she tried to build a new life in the US with her physicist husband, she still struggled to find scientific employment, as the rigid rules of nepotism thwarted her career.

Yet she endured, and established herself as a highly respected nuclear physicist, one of the few pioneering women in that area. Her research advanced the understanding of nuclear fission and contributed to the theory of nuclear structure.

Her work was recognized in 1972 when she became only the third female physicist elected to the National Academy of Sciences. She is also well remembered as an advocate for women in science, for encouraging young scientists and for championing science education.

Known as Trude to her friends and family, Scharff’s early years in Germany were turbulent ones, encompassing the First World War, political unrest and economically ruinous hyperinflation after the country’s defeat in 1918.

At the age of eight she saw Communist revolutionaries being slaughtered by the military in the streets of Munich, where her family lived. Later she would recall having to eat bread bulked out with sawdust. The turmoil continued, with ominous forebodings for German Jews, as Hitler rose to power in 1933.

Amid all this, Scharff obtained a worthy education. According to a memoir by her son Michael, she attended an elite high school for girls. An outstanding student, she developed an interest in physics. Her father had hoped she would study law to prepare for managing the family business, but she was more keen to “understand what the world is made of”, as she later put it.

Moving toward her goal, Scharff entered the University of Munich in 1930. Her education culminated in working toward a physics PhD under Walther Gerlach, of the famous Stern–Gerlach experiment that, in 1922, established the existence of quantized spin in a magnetic field. Her research in condensed-matter physics dealt with ferromagnetism.

But outside events utterly changed her plans and her life. As Nazism spread, Scharff found herself ostracized by colleagues and German Jews began fleeing the country. She was, however, well along in her research. As she told an interviewer in 1990: “I should have left earlier. But since I had started my thesis, I felt I should finish.”

Finish she did, in 1935, but she cut it very close. That was the year the Nuremberg Laws were enacted, defining first Jews and later Romani and Black Germans as “inferior races” and “enemies of the state”. They were effectively barred from German society, and faced harsh penalties for violating the laws. Antisemitic violence grew and Scharff’s parents later perished in the Holocaust.

Aware that it was most certainly time to escape from Germany, Scharff wrote to 35 refugee scientists seeking a position elsewhere. Almost all told her not to come because there was already a glut of refugee scientists – except for Maurice Goldhaber, a young Austrian-Jewish physicist she had met in Germany.

Working on a PhD at the University of Cambridge under Ernest Rutherford, he thought there could be opportunities in England. Moving to London, Scharff eked out a living for six months by selling a prized possession that was part of her wedding trousseau – a Leica camera, well known for its fine optics – and translating articles from German into English.

Then she worked at Imperial College London under George Thomson, studying electron diffraction (in 1937 he shared the Nobel Prize with Clinton Davisson for discovering the effect in crystals), but never found an independent research position.

In 1939 her prospects improved. The nuclear physicist, Scharff married Goldhaber, becoming Scharff-Goldhaber, and the couple moved to the US. Goldhaber had a faculty position at the University of Illinois-Urbana, but Scharff-Goldhaber could not become a full-fledged academic scientist, because anti-nepotism laws in Illinois did not allow the university to hire her.

She could do research only as an unpaid assistant in her husband’s lab. This moved her from condensed-matter physics into his field of nuclear physics. Scharff-Goldhaber’s papers in the 1940s produced under these circumstances show that she handled the transition brilliantly – but she never reached full faculty status at Illinois.

Only in 1950 did, nuclear physicist Scharff-Goldhaber and her husband together find a true research home, at the new Brookhaven National Laboratory (BNL), which had been founded three years earlier. Today a US Department of Energy facility, the lab’s original mandate was to seek peaceful uses of atomic energy. Its scientific efforts have since diversified but nuclear and high-energy physics remain part of its research activities.

Her appointment made Scharff-Goldhaber the first female physicist at BNL, and 15 years after earning her degree, she was finally being paid as a professional researcher. Even so, she operated in an atmosphere that her son Michael describes as only “grudgingly accepting”.

Goldhaber was hired as a “senior scientist” and ran his own research group, but Scharff-Goldhaber was ranked simply as a scientist within his group. (Goldhaber would eventually rise to director of the lab 1961–1973, and Scharff-Goldhaber to senior scientist.)

As the only woman with professional scientific status at BNL, Scharff-Goldhaber had no female scientific peers. Most women associated with the lab were the non-working wives of male scientists, who in the 1950s filled traditional roles.

With two children, Michael and Alfred, Scharff-Goldhaber had similar responsibilities; but at social events she was more likely to talk physics with the men than discuss childcare with the women. Within this male milieu she formed good relationships with her colleagues, and with the support staff who produced the isotopes she needed for her research at the BNL reactor or Van de Graaff accelerator.

Except for the period in the 1930s when she was still trying to become an independent scientist, Scharff-Goldhaber maintained a brisk pace of research and publication, while meeting family obligations. In 1936 she published “The effect of stress on the magnetization above the Curie point” from her thesis.

Her next set of papers began four years later, once she switched to nuclear physics in 1940 at Illinois, and she wrote over a dozen more until she was fully settled at BNL. Over the next 30 years, she published some 60 more papers, mostly in the Physical Review, and contributions to conference proceedings.

Several of the papers arising from her work at Illinois in the 1940s are especially notable, including one that concerned spontaneous nuclear fission. In 1938 Lise Meitner and Otto Frisch had found that a uranium nucleus bombarded with neutrons could split in two and release much energy.

If neutron-induced fission could be made self-sustaining, it could produce an enormously destructive weapon. With war looming, European and American physicists investigated self-sustaining fission hoping that the Nazis would not find the answer first.

In 1942 , nuclear physicist Scharff-Goldhaber directly showed, apparently for the first time, that uranium undergoing spontaneous fission released neutrons along with energy. These neutrons could activate more nuclei and more energy – a cascading chain reaction that could become a nuclear explosion.

Data like these were crucial to achieving the world’s first self-sustaining controlled nuclear reaction in 1942, as the atomic bomb was being built by the Manhattan Project. The nuclear physicist, Scharff-Goldhabers were not yet US citizens and so were not part of the project, but her result was secretly circulated to relevant scientists and was published after the war (Phys. Rev. 70 229).

In a separate paper published in 1948 (Phys. Rev. 73 1472), the Scharff-Goldhabers together answered a fundamental question: are beta rays exactly the same as electrons? Discovered in 1897 in cathode rays by J J Thomson, electrons were the first known elementary particles.

A few years later in 1899, Rutherford was studying the new phenomenon of radioactivity, and found an unknown emission he called beta rays. These turned out to be charged particles with the same charge to mass ratio e/m as electrons and were identified as such. But the question remained: could beta rays and electrons differ in some other property such as spin?

The Scharff-Goldhabers cleverly tested this hypothesis by using the Pauli exclusion principle, which, they wrote, “would not hold for a pair of particles if they differed in any property whatsoever”.

In their experiment, they irradiated a lead sample with beta rays. If these were not identical to electrons, they would not obey the Pauli principle. Then they would be captured by lead atoms, enter bound orbits already filled with electrons, and transition to the lowest orbit, causing X-rays to be emitted.

If beta rays and electrons were identical, the former would be barred from entering atomic orbits and producing X-rays. The experiment detected no X-rays at the expected energies, confirming that beta rays are electrons emitted from radioactive nuclei.

Starting in the early 1950s at BNL, Scharff-Goldhaber began what would be her career-long project: to form a systematic picture of the properties of excited nuclei across the periodic table. Her plan to work in “low-energy” nuclear physics diverged from her husband’s growing interest in “high-energy” physics, where huge new particle accelerators probed fundamental particles.

According to their son Michael, Scharff-Goldhaber’s separate path deprived his father of her great abilities as an experimentalist. But he adds that “the split did not prevent the family dinner table conversation from focusing on nuclear physics, just as it had before, largely to the bafflement of the children”. (Later he and Alfred each earned a doctorate in theoretical particle physics.)

At the time, the behaviour of the excited nucleus was just beginning to be grasped. This dense soup of protons and neutrons could be viewed as a collection of particles bound together by nuclear forces, forming a medium with an energy that is expressed in rotation or vibration of the entire body.

In the so-called “shell model”, however, the nucleus was seen as a quantum system where nucleons occupy energy levels, analogous to the discrete levels or “shells” occupied by electrons in an atom.

Each approach had successes. Treating the nucleus as a liquid led to an understanding of how it could deform and undergo fission. The shell model predicted that nuclei with specific, or “magic”, numbers of protons or neutrons (2, 8, 20, 28…) would be exceptionally stable, again analogous to filled electronic shells in atoms.

It wasn’t clear, however, whether experiment really supported the shell model, or where each approach could best be applied. The nuclear physicist, Scharff-Goldhaber’s extensive research on different nuclei helped to resolve these issues. Her work was significant in developing the theory that finally connected the two approaches, which led to Aage Niels Bohr, Ben Mottelson and Leo Rainwater sharing the 1975 Nobel Prize for Physics.

In the 1950s Scharff-Goldhaber measured the energy of excited nuclei versus neutron number and showed that shell structure influenced the energy, which peaked at the magic numbers. She also noted an anomalous change in energy levels with an increase in the number of neutrons, which she related to a change in shape of the nucleus.

Later she developed her own “variable moment of inertia” (VMI) model, which used the shape of nuclei to provide further insight into their energies across the periodic table.

Besides her contributions to nuclear theory, nuclear physicist,  Scharff-Goldhaber’s research in this era had unusual features. She wrote two papers about the VMI model together with her son Alfred – as far as is known, the only mother–son research papers in physics (Phys. Rev. Lett. 24, 1349 ; Phys. Rev. C 17, 1171).

She also enhanced her data analysis by extending the standard nuclide chart, where each nucleus is placed in a two-dimensional plot of number of protons versus number of neutrons. Scharff-Goldhaber glued vertical rods of length proportional to the lowest excitation energy for each nuclear species to the appropriate position on the chart.

Long before the routine use of 3D computer visualizations, this was a tremendous aid in spotting important features such as the energy change between N = 88 and N = 90.

Along with her research, Scharff-Goldhaber found ways to help women in science, and to contribute to science education and the scientific community.

Among many professional involvements, she served on American Physical Society (APS) committees devoted to the status of women in physics and to pre-college physics education. She was known too for reaching out to early career scientists – both men and women.

One was Rosalyn Yalow, Goldhaber’s PhD student at Illinois, who shared the 1977 Nobel Prize in Physiology or Medicine for inventing the radioimmunoassay technique. Yalow has credited both her adviser and Scharff-Goldhaber “for support and encouragement”.

Scharff-Goldhaber also broadened the intellectual atmosphere at BNL by founding the Brookhaven Lecture Series, featuring eminent speakers such as Richard Feynman.

The nuclear physicist, Scharff-Goldhaber had started at BNL relatively late and was ready to continue her research for a long time, but the stringent retirement laws of the era officially ended her employment in 1977, aged 66.

According to her son Michael, the retirement was forced in a way that he calls “subtly sexist”. Nevertheless, working without pay, she collaborated with other scientists and co-authored research papers until 1988. When failing health restricted her activities, however, she appreciated and sought satisfaction in what she could still do, until she died at the age of 86 in 1998.

In 1990 a journalist interviewing Scharff-Goldhaber noted her “soft but insistent determination” – likely the very character traits that enabled her to overcome barriers to a research career. In 2016, looking back on his mother’s life, Michael described her as “a person of unique wilfulness and even stubbornness, traits that she certainly needed…to pursue a successful career in a world that was often set against her”.

Perhaps nuclear physicist, Scharff-Goldhaber would agree with these assessments, but there’s another one that I believe applies. In 1972, reviewing a book about nuclear energy by Isaac Asimov, Scharff-Goldhaber wrote that progress in science, among other qualities, is “based on the burning desire to get to the bottom of things”. Writing those words, did she reflect that her own life perfectly exemplifies that ethos?

Originally published at Physic World