In 1937, after he unsuccessfully applied for a job with Canada's National Research Council, the University of Chicago accepted Slotin as a research associate. There, he gained his first experience with nuclear chemistry, helping to build the first cyclotron in the midwestern United States. The job paid poorly and Slotin's father had to support him for two years. From 1939 to 1940, Slotin collaborated with Earl Evans, the head of the university's biochemistry department, to produce radiocarbon (carbon-14 and carbon-11) from the cyclotron. While working together, the two men also used carbon‑11 to demonstrate that plant cells had the capacity to use carbon dioxide for carbohydrate synthesis, through carbon fixation.