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  • Writer's pictureDale DeBakcsy

Two Roads Diverged: Marietta Blau, Hertha Wambacher, and the Great Cosmic Ray Chase.

Untold billions of miles away, a star explodes, and violently ejects barrages of hydrogen and helium atoms into the universe at speeds approaching those of light. Brimming with energy, they tear through the cosmos until they reach our planet, where they slam into the particles of our atmosphere, with the resulting explosion sending a rain of smaller particles and electromagnetic radiation down upon the world below. Before we knew just what this phenomenon was, scientists assumed it had to have originated from some form of high energy ray, emanating from space, and so the term Cosmic Ray was coined to describe them. 


Today, we have a myriad of techniques for observing and analyzing the behavior of cosmic rays, but in the 1930s our options were slim indeed, until an unlikely pair of women came together to develop a new way of capturing the path of a cosmic ray, and visualizing its impact upon the particles around it. They were Marietta Blau (1894-1970) and Hertha Wambacher (1903-1950), and while ultimately one of them would become the hero, and the other the villain in their shared story, for one moment in time in 1937 they shared a heady moment of discovery together when their methods revealed to the world the existence of disintegration stars. 


Blau was born in Vienna at the height of its intellectual ascendancy. During her youth the city saw Gustav Mahler at the podium as its reigning musical genius, Sigmund Freud developing his theories of psychoanalysis, Gustav KIimt and the Vienna Secession defining a new path forward for art, and Lise Meitner start a career that would culminate in the discovery of nuclear fission. The progressive Viennese Jewish community placed itself squarely at the center of these developments (Freud, Meitner, and Mahler were all themselves Jewish), and Blau’s father, who worked as a music publisher when he wasn’t doing his main gig as a court lawyer, was fully caught up in the artistic and scientific spirit of the community. We know frustratingly little of her early life until her arrival at the University of Vienna in 1914 to study physics and mathematics. 



Founded in 1365, the University of Vienna was one of the most prestigious institutions in the world at the time, and a center of Austrian cultural life, but had not admitted women as full time students until 1897. That first year, the ratio of women to men in the study body was 1:138, but by the time Blau arrived in 1914 that number had improved to 1:12, with upper middle class Jewish women like Blau making up a significant portion of the influx. Though women were a relatively common sight on the university grounds when Blau matriculated, they were still a rarity in the physics department. She was able, however, to collaborate with women physicists from other parts of Europe, and in particular had a fruitful exchange of ideas with the Hungarian chemist Elizabeth Rona (1890-1981), who was a world expert on the production and use of polonium. 


The work that Blau would become famous for was an outgrowth of a suggestion from her group leader, H Pettersen, that she work on problems related to the use of photographic emulsion as a technique for capturing the activity of particles in the subatomic realm. This was a promising new tool, which relied on the fact that certain particles, when they travel through a photographic plate, interact with the silver halide molecules in the plate in ways that can be used to deduce a number of those particles’ properties. She received her PhD for this work in 1919 and continued improving upon her methods, by 1926 publishing her techniques for capturing the behavior of alpha particles (a particle consisting of two protons and two neutrons) and recoil protons. This was highly important work - the emulsion techniques that existed up to that time were highly fragile, and other methods for charting particle behavior, like cloud chambers, were finicky and difficult to record. Blau’s emulsions were sturdy and clear, and served as a springboard for her investigation of cosmic rays.


Between 1919 and 1923, Blau had been occupied with a variety of industrial jobs and university positions, but from 1923 to her flight in 1938, she resided and worked in Vienna, taking up research positions that carried neither status nor payment, supported by her family’s financial assistance and the occasional grant, a shadowy academic half-existence that would dog her the rest of her career, and keep her consistently from a stability and renown commensurate with the importance of her discoveries. Some time in the mid-1920s, Blau took up Hertha Wambacher as her chief lab assistant. Wambacher had much in common with Blau - they both were products of the high school run by the Association for the Extended Education of Women in Vienna, they both were women interested in physics in a world dominated by men, and they both were gifted experimentalists. Blau, however, was a Jew, and Wambacher was not, and that would be an increasingly important distinction in the years to come.


For the time being, however, all was well. In the 1920s they improved and expanded upon Blau’s early emulsion techniques, and in 1932, the year Wambacher received her PhD, they were ready to apply them to that most elusive of phenomena - the cosmic ray. Cosmic rays had been on the menu for only a few decades by this point, originating from Theodor Wulf’s observation that radiation levels at the top of the Eiffel tower were higher than those at the bottom, suggesting a radiation source coming somewhere from above. In 1912, Victor Hess seized the opportunity of a full eclipse to take a hot air balloon 5,000 meters into the air to measure radiation levels along the way, and discovered that, even with the solar source being blocked, radiation continued to climb with the altitude. 


After making measurements of the penetration of this radiation through varying depths of water, Robert Millikan believed them to be primarily high energy photons, and coined the term cosmic ray to describe them, but by 1930 it was discovered that, since the rays seemed to have preferred directions of travel in the presence of the Earth’s magnetic field, they must have some charge to them, ruling out photons. At that point, the stage was set for Blau and Wambacher to enter with their elegant and finely tuned techniques to unveil the behavior and nature of cosmic rays.


Since every experiment had suggested that the intensity of the rays increased with altitude, they resolved to place their emulsions as high as they could, and ultimately decided on the top of Hafelekar mountain, some 2,300 meters above sea level. Here they not only made the determinations of the high energy and proton count of cosmic rays that other researchers were simultaneously coming to, but in 1937 discovered a new phenomenon entirely - the disintegration star. 


Blau in the Lab.


Most of the emulsion paths the pair had been observing on the mountain for a half decade had been simple arcs, but in 1937 they began seeing arcs that terminated in small branched explosions, starlike in appearance. The implications were profound - the high speed cosmic protons were colliding with larger atoms and causing them to eject numbers of smaller pieces. Their paper, published a year before Lise Meitner’s theorizing of nuclear fission, showed the cracking of the atom, and contributed substantially to the explosion of particle physics as a discipline, while also lending support to the ultimate two-stage explanation of cosmic ray effects - the initial wave of mainly hydrogen and helium smacking into the atmosphere, and producing a second wave of many different particle types that rain down upon the Earth.


It was an exciting result, but Blau did not have long to savor it. The Austrian Anschluss occurred in 1938, and Blau recognized that her work in Vienna could not long continue. While Wambacher remained in Vienna, secure on account of her membership in the Nazi party since 1934, Blau fled, as so many Jewish scientists had before her, first to Copenhagen, then to Oslo, and ultimately to Mexico, where Albert Einstein (who could be decent to women colleagues as long as he wasn’t married to them) secured her a position at the Technical University of Mexico City. While exiting Austria, Blau had her research confiscated by the state, which ended up back in the hands of Wambacher, who proceeded to use it to continue her research and publish new results that did not acknowledge Blau’s founding contributions while Blau was compelled to continually restart her career in new locations across the world. 


Wambacher in the Lab.


As Wambacher flourished, taking up a teaching position at the University of Vienna in 1940, Blau did what she could in Mexico, studying the radiation patterns emerging from radioactive rocks and doing some work on cosmic rays, but not really coming into her own again until 1944, when she moved to New York City to begin a decade of academic wandering, from industry to Columbia University to Brookhaven National Laboratory to the University of Miami, often doing important work (particularly in wedding her emulsion techniques to emerging cyclotron technology to further the study of particle physics), but never staying in one place long enough to build up a position of security. 


Meanwhile, Wambacher’s actions finally caught up with her at war’s end. As a member of the Nazi party who actively profited from the expulsion of her Jewish colleague and usurpation of her life’s work, she was removed from her position at the University of Vienna, and sent to prison in Russia. It was not until 1946 that she was allowed to return to her home country, but years of working with insufficient protection around radiation had taken their toll, and though she continued to work, she ultimately succumbed to cancer in 1950, which several colleagues used as an opportunity to besmirch Blau one final time in the obituaries they published maintaining that Wambacher had been the main actor in the discovery of disintegration stars, and Blau’s role was entirely secondary, a bit of historical rewriting that will be familiar to anybody familiar with Otto Hahn’s post-war recasting of the discovery of nuclear fission to downplay Lise Meitner’s central contributions.  


The specter of radiation also cast its pall over Blau’s final days. The lines on the palms of her hands had disappeared from years of handling radioactive substances, and by 1960 her vision had become seriously impaired, preventing her from working, meaning she also did not have enough money to pay for the operation that might restore her sight, the American health system being what it was (and is). Her only hope was to move back to Austria, where the procedure would be cheaper, but the restoration of her sight only made room for the arrival of heart disease as the next impediment to her resumption of a satisfying career. Erwin Schrödinger nominated her for the Nobel Prize for her work, which would have provided her with some remuneration to save her from her constant financial troubles, but the award instead went to Cecil Powell, who applied her methods to the discovery of pions, rather than to Blau for having originated the method and used it to discover the effect of proton bombardment on larger nuclei. In 1964, Blau was able to return to work in Vienna, at the Institute for Radium Research, which continued the long and grand tradition of allowing her to do research for them without receiving pay. 



Marietta Blau, one of our most assiduous and talented investigators in the great cosmic ray mystery, and a trailblazer in the field of particle physics, died in April of 1970, after a year of intensive hospital care. 


FURTHER READING:


There is a nice volume about Blau and Wambacher by Rosner and Stohmaier which was originally published in German as Marietta Blau - Sterne der Zertrümmerung. Biographie einer Wegbereiterin der modernen Teilchenphysik in 2003, and then translated into English in 2007 (I believe there is also a Spanish translation available). It is not an easy book to find, but if you are trying to complete your Women in Physics bookshelf, you’re going to need it, particularly as it tells more about the political story than you get in the Blau section of Grinstein, Rose, and Rafailovich.


This has been the 254th entry in the Women in Science Archive series.

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