The Lost Women of the Manhattan Project

We recently launched Lost Women of the Manhattan Project, a miniseries about some of the forgotten women who made significant contributions to the three-year effort during World War II to create a bomb that would end the war. We’ve timed the series to coincide with the release of the film Oppenheimer. After releasing our third episode, we received this email from William Brigham, an astute listener:

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‍Almost 20 years ago I read "American Prometheus," the Oppenheimer biography which served as the basis for the current film. As if to prove the obvious I pulled the book off my shelves and checked the index for any of the women scientists you are now featuring. No surprise--and to the very point of your podcast--only one is mentioned in the book, and there is one man with the same last name of one of the women, presumably her husband, whose work was deemed qualified for recognition.

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‍It’s notes like this that reinforce our belief that we’re onto something important here. For every woman we’re profiling in this series, we know there are many more whose stories we’ve yet to tell. Here are a few of them, whose names we’ve culled from “Their Day in the Sun: Women of the Manhattan Project” by Ruth Howes and Caroline Herzenberg. The book has become perhaps the most definitive work on the topic of women who worked on the Manhattan Project.

When Howes and Herzenberg called Joan Hinton to request an interview in 1990, the 69-year-old Hinton told them she had just repaired her car on a solo cross-country bird-watching trip.¹ It was perfectly characteristic of Hinton, who was chronically curious and a natural problem solver.

In 1942, Hinton graduated from Bennington College in Vermont.² For her sophomore project she had created a cloud chamber, a particle detector that visualizes the passage of ionizing radiation. Hinton also spent time at Cornell University, and when its particle accelerator broke down, Hinton eagerly helped repair it — working alongside the very physicists who later recruited her to Los Alamos.³

Hinton flourished both within physics and beyond it. She was known as a dauntless skier at the University of Wisconsin, where she earned her doctorate in 1944, and was constantly in motion. This boded well for her Manhattan Project group, which was headed by Italian physicist Enrico Fermi. Fermi encouraged his young team to play as hard as they worked, leading them on daylong hikes and ski trips.⁴

Fermi’s team built two reactors to test uranium and plutonium. The first was a low-power reactor they made from scratch. When the team first tested it, they guessed how much uranium was needed for a self-sustaining reaction. There were no formal predictions; they just guessed “for fun,” Hinton recalled. “In the spirit of the test, many of the ‘big shots’ came down” — Hinton’s team worked down a cliff from the main laboratory — “and signed their initials on the graph at the place they expected it to ‘go critical,’” the state at which a nuclear chain reaction becomes self-sustaining.⁵

The second reactor was high-powered, stronger than the first and nicknamed “the water boiler” to describe the water that cooled it. Hinton helped design and build its control rods, piled beryllium blocks around its core, and assembled electronic circuits to measure radiation.

At Los Alamos, information was distributed sparingly. When Hinton discovered details of the Trinity detonation test, she snuck to a hill 25 miles from ground zero on the back of a friend’s motor scooter. When the bomb went off just before dawn, “it was like being at the bottom of an ocean of light,” Hinton described.⁶ “Then suddenly the sound reached us. It was very sharp and rumbled and all the mountains were rubbing with it.”

Hinton’s days weren’t always filled with wonder. The detonation destroyed the 100-foot metal tower that held the bomb and turned sand to glass, called trinitite.⁷ She and some colleagues sent the trinitite to mayors, asking if they wanted their cities to suffer the same destruction.⁸ When the U.S. dropped the atomic bombs on Japan, killing hundreds of thousands of Japanese civilians, Hinton was appalled. She advocated against military control of nuclear weapons and became an outspoken peace activist.  

Two weeks after the bombing, Los Alamos physicist Harry Daghlian dropped a piece of tungsten carbide brick directly on a plutonium core.⁹ When he pushed off the radioactive brick, his hand went numb. Hinton drove him to the site hospital, where the doctors took all the metal objects out of his pockets and asked Hinton to measure their radioactivity. “They were so ‘hot’ the counters just jammed,” Hinton said.¹⁰ Within a month Daghlian was dead. For Los Alamos scientists, this event personally underscored the devastating impact of nuclear weapons. As Hinton recalled: “When 150,000 Japanese disappeared into a huge lethal mushroom of radiation, Harry’s death helped bring the lesson home.”

For two years after Los Alamos, Hinton studied at the University of Chicago with Fermi and other Manhattan Project scientists. But she was frustrated with the militarized direction physics had taken. She traveled to China in 1948, where her brother was a dairy farmer with his friend Erwin Engst. She found that designing and building farm equipment quite suited her. Hinton married Engst and they remained in China, raising their three children outside Beijing.

The earliest image Isabella Karle remembers is the back room of a restaurant.¹¹ It served breakfast and lunch and was run by her mom, who taught her reading and arithmetic. At six years old, Isabel Lugoski calculated how much they owed the butcher each week and entered kindergarten at the top of her class despite only speaking Polish. She quickly picked up English and sped through elementary school, skipping a few grades along the way. Her high school chemistry teacher was a woman — rare at the time — who inspired her to become a chemist.

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Isabella attended a post-high school institution, today Wayne State University, for students who wanted to attend college but could not afford to leave home because of the Great Depression. In her chemistry class of 45 students, she stood out as an exceptional student — and the only woman. “Of course you’re going to graduate school,” her professor told Isabella who before then had never even heard of graduate school. She set a new goal for herself: earn a Ph.D.

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After her first semester, one of her former high school teachers told Isabella about a statewide exam for University of Michigan scholarships. The teacher drove her to the exam site and Isabella placed fourth in the state. She transferred to the University of Michigan with a four-year scholarship and stayed for her master’s and Ph.D., which she completed at age 23. Along the way she met and married her husband, Jerome Karle. He was recruited to a Manhattan Project team at the University of Chicago and Isabella joined him after finishing her Ph.D.

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Isabella Karle’s mission for the Manhattan Project was to purify plutonium. She was part of a team that made halites, commonly known as rock salt.¹² Each week Oak Ridge sent her a few lumps of plutonium oxide, which she heated to 1,000 degrees Celsius before collecting its vapor. The vacuum lines that held the material were made of silica, one of the only materials that could withstand the heat. Karle’s Ph.D. research made her uniquely familiar with vacuum lines and equipped for the job.

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“There were, of course, no rules,” Karle said of her Metallurgical Lab (Met Lab) research.¹³ “This was a new element; its chemistry was unknown.” Karle recalled taking the Illinois Central train to a technical library in downtown Chicago, where she looked up what she needed. This included research on uranium, which is chemically similar to plutonium. Ultimately, Karle said she synthesized plutonium chloride in about a dozen different ways. She pioneered the process for growing plutonium chloride crystals and proved that the new compound was stable.¹⁴

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^‍Karle was the most distinguished female chemist the Met Lab employed.¹⁵ Among her honors, she was awarded the Hildenbrandt Award in 1970, the Garvan Medal of the American Chemical Society in 1976, and the Bower Award in 1993. She was the first woman to receive the Bower Award, which recognized her lifetime achievement in three-dimensional molecular modeling.