In the midst of World War II, fears that Germany might be on the cusp of developing an atomic bomb fueled the United States’s nuclear research. But how close were the Germans to actually developing such a weapon? A new study argues not that close, Forbes reports. In research published online before print in Angewandte Chemie, the scientists investigated uranium samples from 1940s German nuclear projects and found no evidence of a self-sustained nuclear chain reaction—the chemical foundations of an atomic bomb. Specifically, the team measured amounts of uranium-236 and plutonium-239—isotopes that occur in small amounts naturally but can be produced in nuclear reactors—and found only minor amounts, the researchers say.