The Calutron Girls were a group of young women, mostly high school graduates, who joined the

Manhattan Project The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...

, the

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...

efforts to develop nuclear weapons at the United States government facility located at Oak Ridge, Tennessee, between 1943 and 1945. Although they were not allowed to know at the time, they were monitoring dials and watching meters for

calutron A calutron is a mass spectrometer originally designed and used for separating the isotopes of uranium. It was developed by Ernest Lawrence during the Manhattan Project and was based on his earlier invention, the cyclotron. Its name was derive ...

mass spectrometer Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a '' mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is us ...

s adapted for separation of

uranium isotopes Uranium (92U) is a naturally occurring radioactive element that has no stable isotope. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in the Earth's crust. The decay ...

. The

enriched uranium Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (238U ...

was used to make the "

Little Boy "Little Boy" was the type of atomic bomb dropped on the Japanese city of Hiroshima on 6 August 1945 during World War II, making it the first nuclear weapon used in warfare. The bomb was dropped by the Boeing B-29 Superfortress ''Enola Gay'' p ...

" atomic bomb for the Hiroshima nuclear bombing on August 6, 1945.

Background

During

, the United States established the

to develop nuclear weapons. This required

uranium-235 Uranium-235 (235U or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exi ...

, the fissionable isotope of uranium. However, the vast majority of uranium mined from the ground is uranium-238, while only 0.7% is U²³⁵. Scientists developed several processes for separating the isotopes of uranium, including electromagnetic separation and gaseous diffusion. The Y-12 factory was built in Oak Ridge, Tennessee to house 1,152

s, a machine used for isotope separation. The word "calutron" is a

portmanteau A portmanteau word, or portmanteau (, ) is a blend of wordsCalifornia University

Cyclotron A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Jan ...

. Calutrons, a variation on mass spectrometers, work by combining uranium with chlorine to make

uranium tetrachloride Uranium tetrachloride is an inorganic compound, a salt of uranium and chlorine, with the formula UCl4. It is a hygroscopic olive-green solid. It was used in the electromagnetic isotope separation (EMIS) process of uranium enrichment. It is one o ...

, which is then ionized and put in a

vacuum chamber A vacuum chamber is a rigid enclosure from which air and other gases are removed by a vacuum pump. This results in a low-pressure environment within the chamber, commonly referred to as a vacuum. A vacuum environment allows researchers to con ...

with a magnetic field. When the charged particles move through the magnetic field, they move in a curve, the radius of which is proportional to the mass of the particles. The two isotopes differ in mass by about 1% and can thus be separated. The operation was relatively simple, but it required people to constantly monitor the calutrons. Due to a labor shortage, there were not enough scientists to operate all of them, and many young men were fighting in the war overseas, so the government recruited farm girls to operate the calutrons instead. Local women were recruited because they were readily available, used to hard work, and were expected not to ask too many questions and to be loyal and docile.

Recruitment and training

The Tennessee Eastman Company, which ran the Y-12 site, recruited around 10,000 local women between 1943 and 1945 to operate the calutrons. They used a large local advertising campaign to recruit workers. One ad read, "When you're a grandmother you'll brag about working at Tennessee Eastman". Several workers heard about the jobs from friends. Reasons for applying included needing the money, having few other employment opportunities, and wanting to help the war effort. Training lasted three weeks.

Life at work

Secrecy and confidentiality were a strict requirement of their employment. According to Gladys Owens, who was one of the Calutron Girls, a manager at the facility once told them: "We can train you how to do what is needed, but cannot tell you what you are doing. I can only tell you that if our enemies beat us to it, God have mercy on us!" Testimonies said women who talked about what they were doing disappeared. One young woman who disappeared was said to have "died from drinking some poison moonshine". If they were too nosy about what they were working on, they were replaced. Cars going in and out were searched, and letters were opened and read. The workers sat on high stools for 8-hour shifts, seven days a week, monitoring gauges and adjusting knobs to keep the needles where they were supposed to be and recording readings. The knobs were labeled with cryptic letters. The women did not know what the letters stood for, but they learned rules such as "if you got your M voltage up and your G voltage up, then Product would hit the birdcage in the E box at the top of the unit and if that happened, you'd get the Q and R you wanted". They had to make sure the machine remained at the correct temperature; if it got too hot, they used liquid nitrogen to cool it down. If the needles reached a point where they could not control them, they had to call someone else to come help. Former Calutron Girl Wynona Arrington Butler said, "We all wore little fountain-pen-sized

dosimeter A radiation dosimeter is a device that measures dose uptake of external ionizing radiation. It is worn by the person being monitored when used as a personal dosimeter, and is a record of the radiation dose received. Modern electronic personal d ...

s. Part of signing out of the plant was to check the amount of radiation that you had absorbed every day." Another calutron device existed at the time in a laboratory at the

University of California at Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant uni ...

, led by physicist

Ernest O. Lawrence Ernest Orlando Lawrence (August 8, 1901 – August 27, 1958) was an American nuclear physicist and winner of the Nobel Prize in Physics in 1939 for his invention of the cyclotron. He is known for his work on uranium-isotope separation f ...

. The facility there was operated by trained professional physicists. As the Y-12 calutron facility at Oak Ridge became operational, Lawrence desired that it be also run by physicists. Because of the labor shortage during World War II, the staffing went to farm girls instead. In a weeklong contest, the women outperformed the scientists in efficiency of calutron operation. The better performance of the women was attributed to their intense focus to maintaining precise control, as opposed to the physicists, who were distracted by chasing operational problems. Some Calutron Girls had more of a sense of what they were working on than others. Wynona Arrington Butler, who had some training in chemistry, said she and others with a similar background had some sense of what they were doing. They knew they were producing "the Product", and they guessed it was somewhere near the bottom of the periodic table. Willie Baker, on the other hand, said, "Even when somebody let it slip that we were building a bomb, I didn’t know what they meant. I was just a country girl. I had no understanding of what an atomic bomb was."

Bombing and aftermath

Over two years, the calutrons at Y-12 had produced about of U²³⁵. This was enough to make the first atomic bomb. On August 6, 1945, when the US dropped the first bomb, "Little Boy," on Hiroshima, Japan, the Calutron Girls were finally told what they had been working on. Some women were working and others were in their dorm rooms when someone came and told them that an atomic bomb had been dropped on Japan, and everyone there had played a part in making it. Several Calutron Girls had mixed feelings about their part in the bomb. Ruth Huddleston said she was really happy at the time, because her boyfriend was stationed in Germany, and this would bring him back. It bothered her that she had a part in killing so many people, but she accepted that "if the bomb hadn’t been dropped, then probably more people would have been killed. ... But even today, if I think too much about it, it bothers me." Wynona Arrington Butler had a similar experience: at the time, she was happy that the war was over and people she knew in the service could come home, but over time, she began to question whether it was the right thing to do. As of 2020, only a few elderly Calutron Girls remained. Some, such as Ruth Huddleston, regularly shared their stories with the public, often alongside Oak Ridge historian Ray Smith. The women are the subject of the nonfiction book ''The Girls of Atomic City'' by Denise Kiernan and the novel ''The Atomic City Girls'' by Janet Beard.

Background

Recruitment and training

Life at work

Bombing and aftermath

See also

References

Further reading