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Darleane Hoffman with the instruments she uses to track down heavy elements. Photo courtesy Lawrence Berkeley National Laboratory.
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About Her Life
Darleane Hoffman (born 1926) grew up in Iowa. Her father was a school principal who sometimes taught math and coached girls' basketball as well. After high school she entered Iowa State College (now Iowa State University), where she first majored in applied art but later changed her major to chemistry. She was inspired by her chemistry professor, Nellie Naylor. Hoffman had some qualms because many women who went into science in those days had to choose between having a career and having a family. Naylor herself had chosen career over family and never married. Hoffman knew she wanted a family as well as a career and was inspired by the story of Marie Curie, who made many scientific discoveries, winning two Nobel prizes, and also raised two daughters. Curie's life inspired Hoffman to go ahead with her plans to pursue science.
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After graduation Hoffman stayed at Iowa State to earn her Ph.D. There she met and married her husband, Marvin Hoffman, also a grad student. Darleane graduated first and went to work at Oak Ridge National Laboratory in Tennessee, while Marvin remained in Iowa to finish his Ph.D. This separation was unusual for the time, but the Hoffmans were soon reunited when Marvin finished his doctoral experiments and moved to Oak Ridge to be with Darleane while he wrote his dissertation. When Marvin graduated, both Hoffmans went to work at Los Alamos National Laboratory in New Mexico, where they researched nuclear chemistry.
Hoffman became known for a number of important discoveries. She was the first to discover a naturally occurring element heavier than uranium. Roughly speaking, the “heavy” elements that Hoffman studies are elements with high atomic masses and an atomic number greater than 92; that is, an atomic number greater than that of uranium. Plutonium is one example of a heavy element. Its isotopes (“species” of plutonium) have atomic masses like 244 or 239, and its atomic number is 94. These heavy, transuranium elements generally do not exist in nature; they are created or discovered by scientists in the lab. The first one, neptunium (atomic number 93), was discovered in 1940, and plutonium was discovered in 1941. For years, scientists believed that elements having a higher atomic number than uranium did not occur in nature. But it was Hoffman who discovered small amounts of a plutonium isotope (plutonium-244) in a rock formation that was several billion years old.
Though many transuranium elements have been created in the laboratory, not much is known about their chemistry. Most of these elements are so radioactive that they quickly decay into other elements before they can be studied. Hoffman carried out a rare study of the chemistry of the element hahnium, also called dubnium. Using an isotope called hahnium-262, which has a half-life of only 35 seconds (she had to work fast!), she was able to study how the element behaved both in aqueous solution and in the gas phase. She could be a little more relaxed when she studied the same properties of lawrencium-103. Its half-life is a whopping three minutes!
Along the way, Hoffman also made an important discovery about nuclear fission, that is, the splitting of the nucleus of an atom. It had been known since the late 1930s, when nuclear fission was discovered, that the nuclei of certain elements split when bombarded with neutrons. But in the early 1970s Hoffman discovered that the atoms of one element, fermium, could split spontaneously, without anyone shooting a single neutron at it.
Nuclear safety is also a concern to Hoffman. She helped investigate nuclear weapons test sites to see if dangerous radioactive materials were leaking into the environment. She is also interested in the safety of nuclear power. While nuclear power can be used to generate electricity without producing greenhouse gases or other kinds of air pollution, it does produce solid radioactive waste. Hoffman was part of a team that investigated the possibility of storing this hazardous radioactive waste at a remote desert site deep underneath Yucca Mountain in Nevada.
Hoffman worked at Los Alamos National Lab from 1953 to 1984, when she left to become a professor at the University of California, Berkeley, and researcher at the affiliated Lawrence Berkeley National Laboratory. There she was involved with the discovery of new superheavy elements, including the elements 114 and 116.
Hoffman’s achievements have not gone unnoticed by the scientific community and beyond. She received the National Medal of Science in 1997, the Priestley Medal in 2000 from the American Chemical Society, and numerous other honors. In addition to having a long, productive career, Hoffman has also managed to have a full family life, as she and her husband have two grown children and several grandchildren.
For Further Reading on the Web
Darleane C. Hoffman — Hoffman's faculty page on the University of California, Berkeley, Web site. |
