In the wake of the Second World War—and the nuclear bombing of Hiroshima and Nagasaki—there was a flourish of scientific interest in the potential health effects of radiation exposure. Among the experts to probe this topic was Liane Russell, a geneticist who researched the impact of radiation on developing mice embryos. Thanks in large part to Russell, who died on July 20 at the age of 95, medical professionals today take careful precautions when administering radiological procedures to women of child-bearing age.

According to Emily Langer of the Washington Post, Russell died of pneumonia after undergoing chemotherapy for lung cancer. In an obituary, her family remembered her “heroic spirit, lively curiosity, intelligence, optimism, sense of humor, and love of chocolate.”

Russell was born Liane Brauch in Vienna in 1923. Her mother was a singing teacher, and her father was a chemical engineer. According to the family obituary, Russell’s parents “encouraged [her] inquiring mind, treated her as a rational being, and convinced her that girls could do anything boys could.” But it was a dangerous time for the Brauchs and other Europeans with Jewish heritage. Russell was 14 years old when the Nazis invaded Austria. She and her family were able to flee to London, though they had no choice but to relinquish their home, all their possessions and Russell’s father’s business.

The family survived the London Blitz and eventually immigrated to the United States. Lee studied chemistry and biology at Hunter College and, in 1943, secured a summer job at the Jackson Laboratory, a biomedical research facility in Bar Harbor, Maine. Her supervisor there was William Russell, a prominent geneticist who would become Russell’s husband and her research partner.

In 1947, the couple moved to Tennessee to work at the Oak Ridge National Laboratory (ORNL), formerly a secret Manhattan Project site where scientists conducted nuclear research. Liane and William decided to accept jobs at this particular lab because it allowed them to work together, and they quickly set about studying the effects of radiation exposure on mice. The rodents share around 80 percent of their genes with humans and undergo a number of similar biological processes, which is why they are often used as human proxies by medical scientists. At Oak Ridge, Liane and William established the “Mouse House,” which eventually came to hold 200,000 mice used for genetics research.

As part of Liane’s graduate dissertation—she obtained her Ph.D. in zoology from the University of Chicago in 1949, according to Katharine Q. Seelye of the New York Times—she was investigating the harmful impacts of radiation exposure on mice embryos at various stages of development. She observed, for instance, that exposure to radiation on a specific day of development led to one foot deformity, and to another foot deformity when the embryos were exposed to radiation the following day. At yet another point, radiation exposure seemed to cause truncated tails.

Based on these and other findings, the Russells determined that the most critical period of human gestation spans from two to six weeks, when many women do not yet know that they are pregnant. In 1952, the couple published a paper in the journal Radiology recommending that women who might become pregnant only undergo radiological procedures—like X-rays—during the two weeks after the onset of their last menstrual cycle, when they are unlikely to be pregnant.

Such precautions are now ubiquitous in the medical field. But at the time, the couple’s findings were controversial. “These recommendations, published in 1952, brought the wrath of radiologists down upon our heads, and unleashed a series of letters to the editor,” Liane once wrote, according to the ORNL. “Before long, however, the so-called 14-day (sometimes 10-day) rule became internationally accepted in radiological practice.”

Liane Russell’s research also led to the crucial discovery that the Y-chromosome determines maleness in mice. Her research marked the first time that this phenomenon had been shown to occur in mammals and, according to Seelye, set off “a scramble among scientists to see if this was the case in humans too, which it was.”

Russell was well-decorated for her pioneering work. She was awarded the Roentgen Medal in 1973, became a member of the National Academy of Sciences in 1986 and, in 1994, received the prestigious Enrico Fermi Award from the Department of Energy.

She never took for granted that, as a woman working in the 1940s, she had been able to forge a fulfilling career in the scientific field. “In my life, I was very fortunate in being given opportunities to pursue my own ideas in exciting research areas,” Russell once said. “But this is, sadly, not the case for many young women hoping for scientific careers and ending up in merely supporting roles, perhaps doing only routine jobs.”

In 2013, the ORNL honored Russell by creating the Liane B. Russell Distinguished Early Career Fellowship, a three-year program that seeks to foster long-term career opportunities at the lab—particularly for minority and female scientists.