Bibha Chowdhuri, linocut, 11" x 14" by Ele Willoughby, 2025
The second Printer Solstice prompt is 'even', so I made a portrait about the discovery of mesons. When students are introduced to quarks, the fundamental particles, usually they learn how nucleons, that is, protons and neutrons are each made of trios of quarks. Quarks are weird because they have fractional charge (like +/- a third or two thirds of and electron's charge), and we only ever observe integer charge (say, things have, for instance -1e, 0 or +1e charge). They come in perfectly ridiculously named flavours: up, down, top, bottom, charm and strange (and of course, anti-up, anti-down, anti-top, anti-bottom, anti-charm and anti-strange). Little groups of three quarks can be stable and long-lived, and in fact, a significant proportion of the mass of regular, every day matter, what we call baryonic matter, can be explained by trios of quarks in neutrons and protons. So you can make a proton (+1e) with two up quarks (+2/3 e each) and one down quark (-1/3 e) and the math works out. But it's also possible to make matter with even numbers of quarks. These unstable particles are called mesons. Usually they are made with quark-antiquark pairs, but there are also some exotic mesons with four quarks. Long before we had developed the Standard Model and before quarks themselves were proposed (by Gell-Mann and Zweig, in 1964) as an explanation for baryonic matter, mesons were proposed as an explanation for nuclear forces (what held the neutron and the proton within the nucleus - a real mystery as this force must overcome electromagnetic repulsion) by theorist Hideki Yukawa in 1934 and they were first observed by Bibha Chowdhuri (1913-1991) and her supervisor Debendra Mohan Bose in 1940. In the early days of particle physics, before physicists were accelerating and smashing particles together at incredible speed and energies, the easiest way to observe these particles was in naturally occurring cosmic rays or high-energy ionizing radiation from space which rains down on our atmosphere. Physicists literally climbed mountains and used hot air balloons to get as much altitude as possible to measure these particles. At the time, Chowdhuri, Bose and others called these particles they observed in cosmic rays "mesotron showers" but we now know them as mesons. Seven years after Chowdhuri and Bose published their discovery another physicist, Cecil Powell performed similar experiments. He was granted the 1950 Nobel Prize for working on photographic methods of studying nuclear processes and his subsequent "discovery" of the pi-meson. He had access to higher quality of photo emulsion than his Indian colleagues did during WWII, but his measured mass for the particle was very similar to their results. He did acknowledge their work during his Nobel acceptance (well, he called her "Chaudhuri") but essentially, he repeated their discovery with somewhat higher precision, as well as observing muons decay into electrons. The photographic emulsion method itself, in turn, was pioneered by another under-appreciated woman, Marietta Blau (and her student Hertha Wambacher). Blau was also nominated for, but did not win, the 1950 Nobel Prize. Blau discovered what she called "disintegration stars" which were particle tracks of high-energy cosmic rays nuclear reactions recorded in photographic plates; as a Jewish Austrian scientist, her research was interrupted in 1938; mercifully, she was able to secure a position in Oslo and leave Austria, but having to flee for her safety negatively impacted her career and delayed recognition of her research. One could easily argue that Chowdhuri, Bose, and Blau were at least as qualified to win the 1950 Nobel as Powell.
Bibha was born in Kolkata, to a family of the landlord Zamindar class. Her father Banku Behari Chowdhuri was a doctor. Her mother, Urmila Devi's family were followers of Brahmoism, a reformist religion which branched off of Hinduism, rejecting polytheism, rituals and the caste system. To marry her mother, Banku had to convert and was outcast from Hindu society. He even lost the right to his parent's property. Education of women in India at that time was quite rare, but Brahmo Samaj, the societal aspect of the Brahmoist religion, promoted education, especially of women and girls. Several of the Chowdhuri children (Bibha had four sisters and one brother) were highly and equally educated, while in pre-independence India, the education of girls was so extremely rare as to be virtually non-existent; their expected role was to marry and serve their husbands. None of the Chowdhuri siblings married, which was a rare privilege at the time for the girls.
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| Detail of my screen print "Cloud Chamber" showing particle trails in yellow as recorded in a Wilson Cloud Chamber against a cloudy blue sky. |
She studied physics at the Rajabazar Science College of Calcutta University, where she was the only woman in a class of 24 to graduate with an M.Sc. in 1936. She joined the Bose Institute in 1939 to study cosmic rays with the legendary Debendra Mohan Bose, who had worked with C.T.R. Wilson to build the Wilson Cloud Chamber (a tool for recording the tracks of high energy particles in a supersaturated cloud-like vapour or water or alcohol). He has been reluctant to take her on as a student, and told her he did not have any projects suitable for a woman, but she persisted. He had built a cloud chamber on his return to India, and was building his reputation as India's first cosmic ray physicist. She published her paper in the Transactions of the Bose Institute based on photographic plates exposed to cosmic rays for four months at an altitude of 12,000 feet (3600 m) atop Sandakphu, a mountain peak in Nepal, shown in my portrait. She set up the instrumentation at each site and gathered the exposed plates afterwards for analysis, travelling on horseback - a potentially scandalous action for an unmarried Indian woman in the 1930's. Her research showed the superiority of using photographic plates to employing cloud chambers, and the Bose Institute thenceforth adopted photographic plates.
Next, she proceeded to expose Ilford R2 and the new halftone photographic plates at three different altitudes at Darjeeling at 7000 feet (2000m), Sandakphu at 12,000 feet (3600 m) and Pharijong at 14,000 feet (4300 m), to study what they called "mesotron showers." Yukawa had proposed the particles we now call mesons, to explain the strong nuclear forces which confine protons and neutrons within the nucleus, just a few years previous, and the race was on to confirm their existence. She exposed plates directly to air, and some under paraffin wax or water. Plates were exposed for 150 to 202 days. Using a high-power microscope, she and Bose examined the lengths, spacing and scattering of the recorded tracks to determine the mass, energy and momentum of the particles they recorded. Scattering angle could be linked to mean energy, and the mean grain spacings along tracks could be used to calculate velocities. They found that most tracks were from particles of higher velocities and lower kinetic energies than protons, suggesting, importantly that they were lower mass than protons, as expected fro Yukawa's theoretically proposed particle. She published four papers in Nature from 1940-1942 with her results. Bibha Chowdhuri was the first person to measure the mass of a meson and she quickly published even more precise results. She realized they would need improved photographic plates to continue the research, but these were unavailable due to imposed WWII restrictions. Cosmic ray research at the Bose Institute stopped.
Chowdhuri went to England to pursue her doctorate and join the cosmic ray research laboratory of Patrick Blackett in 1945, with thesis advisor J.G. Wilson, when extensive air showers in cosmic rays was the hot topic in particle physics. She recorded the spectrum of penetrating extensive air showers taking photographic plates within a cloud chamber surrounded by Geiger counters. She defended her thesis, "Extensive Air Showers associated with Penetrating Particles," in 1949. Extensive Air Showers refers to the cascade of subatomic and ionized nuclei particles that we get when cosmic rays enter our atmosphere from space and collide with the nuclei of various air molecules (discovered by Bruno Rossi in 1934); it then extends itself through several more generations of collisions as shown in my portrait. Interviewed by the Manchester Herald, Bibha said, "Women are terrified of physics - that is the trouble. It is a tragedy that we have so few women physicists today. In this age when science, and physics particularly, is more important than ever, women should study atomic power; if they don't understand how it works, how can they decide how it should be used? I can count the women physicists I know, both in India and England, on the fingers of one hand." The same year, Blackett had won the Nobel for "his development of the Wilson cloud chamber method, and his discoveries therewith in the fields of nuclear physics and cosmic radiation."
Chowdhuri applied to do post-doctoral work in Paris at École Polytechnic with Louis Leprince-Ringuet on photo emulsions, seeking financial support from the government of India. She had a letter of recommendation from J.G. Wilson who was one of her thesis examiners. Her application was sent to Homi Babha for comment and he wrote Wilson to inquire whether it would really be worth the investment for her to study photo emulsions for 6 months when her doctorate was on extensive air showers. Both men seem to have forgotten her prior world-class research on photographic methods with Bose, and Wilson backed off his prior recommendation and replied that, "Miss Chowdhuri cannot be regarded as a first-class physicist but she can make good progress under fairly done guidance" and as she had done good work on air showers, she should "not be encouraged to go into a new field of work." Yet, it was photo emulsion work which led to Powell's Nobel.
After her brief stay in Paris she returned to India to work at the Tata Institute of Fundamental Research (TIFR), with a glowing recommendation from Blackett (in complete contrast with Wilson's lukewarm support). She worked as a Research Fellow with the Experimental Physics Group for 5 years, the first woman at TIFR. This was the lowest rank at which they could hire her; all the contracts were written with the presumed pronoun for a physicist of "he." She was in charge of the Cloud Chamber Group investigating penetrating particles in extensive air showers.
She decided to apply for a Senior Research Fellow position in the cosmic-ray project at Bengal Engineering College, Shibpur in 1954. The post had a lower salary and the college was not known for basic research. Her reasons for this decision are unclear, as are Bhabha's for writing her a letter or recommendation but not trying to persuade her to stay. Perhaps she wished to be closer to home, but within a year she left for Paris where she worked with Leprince-Ringuet and studied many new K mesons in cloud chambers in the Alps. While in Paris, her American colleague, a Visiting Fullbright Scholar Wayne Hazen invited her to teach at the University of Michigan. She spent two years working with him and as a Visting Lecturer in physics at the University of Michigan, then worked briefly in Bruno Rossi's MIT lab working on Plastic Scintillators for detecting large air shows and collaborating on planning a new extensive shower array in New Mexico.
In 1961 she joined the Physical Research Laboratory (PRL) in Ahmedabad. Despite her two decades of experience she was only offered a temporary position as a Senior Research Fellow but she was interested and took the job. After beginning her career studying extensive air showers high in the Himalayas, at PRL she investigated high energy muons in cosmic rays at a depth of 700 feet (2000 m) in the Kolar Gold Field with simultaneous measurements at ground level at TIFR in collaboration with Vikram Sarabhai, director of PRL. She and her students and technicians donned miner's hats to descend daily in the elevator cage down to their instruments, sometimes carrying their own oxygen if conditions were unsafe. Sarabhai's untimely death interrupted her future research plans. Once again she saw her research interrupted by factors beyond her control.
After retiring from PRL she returned to Kolkata and continued her research, collaborating with colleagues at Calcutta University, the Saha Institute of Nuclear Physics, the Variable energy Cyclotron Centre and the Indian Association for the Cultivation of Science looking at nucleus-nucleus interactions at relativistic energies to learn about astrophysics and cosmic rays.
She was publishing research until the end of her life, though after returning to India, she chose to publish only in Indian journals. She was never made a fellow of any of the Indian scientific societies. She was woefully under-appreciated during her lifetime; it seems likely she faced gender discrimination and was underestimated by her male peers. She became less and less remembered internationally, and when she died in 1991 no obituary appeared in any scientific journal, but her story and accomplishments have begun to be recognized posthumously. In 2019, the International Astronomical Union named a star "Bibha," Bengali for "ray of light," in her honour. In 2020, when then Indian government decided to establish 11 named research chairs after famous women scientists, the physics chair was named after Bibha Chowdhuri.
References
Bibha Chowdhuri, Wikipedia, accessed December, 2025
Bibha Chowdhuri, Mirror Wellesley Blog, accessed December, 2025
Bhattacharya, Amitabha. The woman who could have won a Nobel. The Telegraph, November 28, 2018.
Jacob, Julie. Bibha Chowdhuri: A Missed Nobel Prize and an Unfulfilled Prophecy. The Lovepost. January 14, 2021.
Mondal, Naba K. Bibha Chowdhuri and Her Remarkable Scientific Endeavours. Resonance. Vol. 28, no. 10, DOI: https://doi.org/10.1007/s12045-023-1686-1. October, 2023
Nagarajan, Archana. Bibha Chowdhuri. Sci-Illustrate. August 8, 2019.
Sinha, Atreyee and Ritam Sinha, Bibha Chowdhuri: A Ray of Light. Building from Diversity, CTAO News. November 30, 2022.
Roy, S.C. and Rajinder Singh. Bibha Chowdhuri - Her Cosmic Ray Studies in Manchester. Indian Journal of History of Science. 53.3 (2018) 356-373. DOI: 10.16943/ijhs/2018/v53i3/49466
Roy, Suprakesh and Rajinder Singh. Bibha Chowdhuri - The First Woman Scientist at the TIFR. Physics News Tata Institute of Fundamental Research, Vol 51 (1-2), Jan-June, 2005
The Nobel Prize in Physics 1948, NobelPrize.org, accessed December, 2025
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