She invented the method. They kept her notebooks.

Every photograph of a subatomic particle collision descends from a technique worked out in an unpaid position in Vienna between the wars.

The woman who worked it out was told, when she asked about promotion, that she was a woman and a Jew, and that this was just too much.

Her name was Marietta Blau.

What she was trying to see

Blau was born in Vienna on 29 April 1894, into a prosperous Jewish family. Her father was a court lawyer and a well-known music publisher. She took her Matura with distinction, studied physics at the University of Vienna, and completed a thesis on the absorption of gamma rays in 1919, at twenty-five.

Academic positions in physics were not available to her. She went into industry, moved to Berlin in 1921 to work for a manufacturer of x-ray tubes, then took an assistantship at the Institute for Medical Physics in Frankfurt am Main, teaching radiology to medical students.

In 1923 she returned to Vienna to care for her mother and joined the Institut für Radiumforschung, one of the three leading radioactivity institutes in the world at that time. Her position there was mostly unpaid. She stayed for fifteen years.

The problem she took up was a practical one. Physicists studying the nucleus could detect charged particles with a Geiger counter and watch them with a cloud chamber, but neither instrument recorded well. A researcher could sit in a dark room for hours watching for scintillations and come away with an impression rather than a document.

Blau went at it through photography. A particle passing through a photographic emulsion disturbs the grains along its path, and the disturbance can be developed and fixed like any other image. The track becomes permanent. It can be measured, filed, and argued over.

The existing emulsions were unreliable and fragile. Blau spent years reformulating them, working through chemistry, film types, and development processes, and corresponding with the manufacturers Agfa and Ilford to get plates made to her specification. She was the first to use nuclear emulsions to detect neutrons, which carry no charge, by recording the protons they knocked loose.

The stars

Cosmic rays are absorbed by the atmosphere, so the experiments had to go up. Beginning in 1932, Blau and her assistant Hertha Wambacher left specially prepared plates at Victor Hess’s observatory on the Hafelekar, a mountain above Innsbruck, roughly 7,500 feet above sea level.

The plates came back with proton tracks, as expected. In 1937 they also came back with something else. A handful of tracks did not run in lines. They radiated outward from a single point, like the spokes of a wheel. One had eight of them.

Blau reported the finding to Nature and called them disintegration stars, Zertrümmerungssterne. What the plates had caught was a heavy nucleus, silver or bromine in the emulsion itself, being shattered by the impact of an incoming cosmic-ray proton.

The historian Ruth Lewin Sime’s assessment is the one usually quoted: by showing that emulsions had come of age for reliably recording high-energy nuclear events, the discovery launched the field of particle physics.

Blau was forty-three. She had a method, a result, and no permanent position.

1938

The obstacles were the ones she had lived with for fifteen years, sharpened by politics. The Radium Institute had no money for her. Austrian universities had no post for her. Antisemitism was already policy in Germany and hardening quickly in Austria.

Wambacher, the assistant who had stood beside her at the Hafelekar plates for six years, was a committed Nazi. So were several of Blau’s other colleagues at the institute. According to the account assembled by the Science History Institute, drawing on the work of the historian Peter Galison, they were maneuvering before the Anschluss to take credit for her work and to have her removed.

Germany annexed Austria in March 1938. Blau left within days, first to Oslo, on a temporary post arranged by a chemist friend at the university there. She later wrote that she was perhaps the last Austrian to pass the German border.

Albert Einstein worked his contacts on her behalf. In 1941 he wrote to the Mexican Minister of Education describing her as a very capable experimental physicist who could render valuable service to the country. She and her mother had already reached Mexico City in November 1938.

Mexico kept her alive. Everyone she had left in Vienna who did not get out was subject to what followed.

What she could not take with her

She could not take the notebooks.

Fifteen years of emulsion formulations, exposure logs, plate measurements, and development records stayed in Vienna, on the shelves of the institute, in the hands of the people who had spent the previous year working to remove her.

Wambacher and the others went on publishing through the war on emulsions and cosmic rays, building directly on the research they had inherited, and acknowledging Blau barely or not at all.

This is the part that does not require a Nobel Committee to explain. A woman was driven out of a country, and the work she had to abandon at the door was picked up and continued by the person who had helped drive her out.

In Mexico there was no equipment and no money. Blau taught undergraduate physics and did routine industrial work to support herself and her mother. She reached the United States in 1944, worked for New York firms, took an academic post at Columbia in 1948, and moved to Brookhaven and the Atomic Energy Commission in 1950, where she finally had accelerators and current instruments to work with.

By then the field she had opened had moved on without her. Cecil Powell, at Bristol, had refined the emulsion method for large teams and used it to identify the pion in 1947. The 1950 Nobel Prize in Physics went to him.

Erwin Schrödinger had nominated Blau for that prize. He nominated her twice. The first nomination named two women: Marietta Blau and Hertha Wambacher.

Sime’s verdict on the outcome is exact. For Marietta Blau, the 1950 Nobel Prize completed the expulsion that the Nazis had begun twelve years before.

After

Blau spent several years at the University of Miami, working with emulsions while the field moved to bubble chambers. Galison’s observation is that the emulsion was an instrument well suited, however awkward its images, to those on the margin. It was cheap, portable, and required no institution.

She returned to Vienna in 1960, after twenty-two years away, and took up an unpaid position at the Radium Institute. The same building. The same arrangement. She lived on small pensions from her American jobs and help from surviving family, and could not afford health insurance.

Decades of handling radioactive sources had ruined her eyes. She went back to Vienna in part because she could not pay for the operation in the United States.

She died on 27 January 1970, of cancer and heart disease, in a Vienna hospital. Her death was not noted by the scientific community.

The tracks are still the standard image of particle physics. The method still carries no one’s name.

The archive grows. The silence shrinks. Enter the archive.

Sources:

• The Dark Stars of Marietta Blau — Mark Wolverton, Distillations, Science History Institute, 10 August 2021. Source for the Hafelekar work, the promotion remark, and the Wambacher account.
• Marietta Blau — Maria Rentetzi, Jewish Women: A Comprehensive Historical Encyclopedia, Jewish Women’s Archive. Source for the birth date, the 1919 thesis, the Einstein letter, and the Schrödinger nominations.
• Marietta Blau’s Work After World War II — Arnold Perlmutter, arXiv. Account by a colleague of her Brookhaven and Miami years, later translated for the Strohmaier and Rosner volume Sterne der Zertrümmerung.
• Marietta Blau, PhD — Association for Women in Science
• C. F. Powell, Nobel Prize in Physics 1950 — The Nobel Foundation. The prize citation, for development of the photographic method and discoveries regarding mesons.
• Peter Galison, “Marietta Blau: Between Nazis and Nuclei,” Physics Today 50, no. 11 (November 1997): 42–48. The standard scholarly account. No open-access edition.
• Ruth Lewin Sime, “Marietta Blau in the History of Cosmic Rays,” Physics Today 65, no. 10 (2012): 8. Print and paywalled, no open-access edition.