Since 1981, six new elements have been added to the Periodic Table found in every chemistry textbook. We talk with Darleane Hoffman — a pioneer in the search for rare, unstable elements.
Darleane Hoffman is a world-renowned nuclear chemist. But when she enrolled in Iowa State College in the 1940s, her plan was to study art.
Darleane Hoffman: And one of the required courses you had to take was freshman chemistry. And that was taught by a marvelous woman, professor Nelly Naylor . . .And chemistry seemed so beautifully logical. But also she pointed out the applications of the chemistry we were learning and how chemistry was a part of everyday life in all respects . . .
Hoffman decided to switch to chemistry, and in the early 1950s began working at Los Alamos National Laboratory in New Mexico. That was around the time of the first nuclear weapons tests in the Pacific, and she helped look for new chemical elements in the debris.
In the 1970s, she headed a team that was the first to discover in nature a rare form of plutonium — plutonium 244. Her team confirmed the existence of element 106 — seaborgium — in 1993. She’s now based at Lawrence Berkeley National Laboratory in Berkeley, California.
She’s now trying to discover a certain new kind of element predicted by experimental chemists — what are called “superheavy elements.”
Darleane Hoffman and her team of graduate students pioneered a technique for studying the chemical properties of just a few atoms of elements that decay in less than a minute.
Darleane Hoffman studies very heavy, very unstable elements at the edge of the Periodic Table — elements that may only exist for seconds before breaking apart into more stable components.
Hoffman’s group is currently working on a set of new elements called the superheavy elements or SHEs. The existence of these elements was predicted as early as 1955, but the search was all but abandoned in the 1980s, when there was still no confirmed evidence for their existence. Scientists were spurred along in their search for the SHEs by the theoretical predictions of an “island of stability” — a zone in the periodic table where the electron configuration in the nuclear shells should make the elements stable. The zone was predicted to be around the atomic numbers 114 or 126. Flanked by neighboring elements with extremely short half-lives, these elements were predicted to have half- lives as long as a billion years. However, although an isotope of element 114 was discovered in 1999, its half-life is on the order of 5 seconds. Two new isotopes of 114 have since been discovered, but none yet demonstrate the predicted stability.
Hoffman received the President’s Medal of Science in 1997. And in 2000, she received the Priestley Medal — the highest honor from the American Chemical Society.
Hoffman’s love of nuclear and radiochemistry began when she entered the college of Home Economics at Iowa State College (later University) as an art major, and took a required course in freshman chemistry. Her professor, Ms. Nellie Naylor, was an inspiration. In Hoffman’s words, Ms. Naylor taught all of chemistry’s applications along with its theories, and “made it seem so beautifully logical.”
After switching her major to chemistry, Hoffman began work as an undergraduate researcher at the Institute for Atomic Energy, on the Iowa State campus. She went on to a Ph.D. program in chemistry and used the synchrotron at the IAE to irradiate organic metal complexes with photons and look for new isotopes and elements.
Hoffman graduated from her Ph.D. program a year earlier than her new husband, Marvin, and she went to work at Oak Ridge National Laboratory for a year while he finished up. “I went off to Oak Ridge to accept a position, because frankly I needed the money. My father had passed away very suddenly during, of a heart attack, during my second year in graduate school. My little brother was five years younger, so I essentially became sort of the family manager, and I felt that I needed to take a job, and left Marvin behind to finish his Ph.D. And in those days everyone thought that was rather scandalous, that I would go off and take a job somewhere else while he stayed there.” Indeed, during that time, Marvin’s advisor warned him that the marriage was a “horrible mistake” and that it would never work out. But work out, it did. The Hoffmans have been married for more than 50 years.
In the early 1950s, Hoffman was invited to help look for new chemical elements in the debris from the first nuclear weapons tests in the Pacific. But her security clearance was lost during the hiring process, and she was sidelined from research for three agonizing months. Darleane Hoffman says, “So by the time they called the FBI to start my clearance over, in March, the two new elements Einsteinium and Fermium, elements 99 and 100, had been discovered in the debris from that test and I had missed being a discoverer, because of that. I’ve never gotten over it.”
In a recent email, Hoffman wrote a brief biography of her achievements: “She headed a team in the 1970s that first discovered in nature a rare form of plutonium — plutonium 244, the longest-lived isotope of plutonium. In 1984, she went to Berkeley to head the Heavy Element Nuclear & Radiochemistry Group (formerly led by Prof. Glenn T. Seaborg) at the Lawrence Berkeley National Laboratory and be Professor in the Department of Chemistry at the University of California in Berkeley. She and her group (primarily graduate students) pioneered techniques for studying the nuclear and chemical properties of just a few atoms of elements that decay in a minute or less. In 1985 they performed the first aqueous chemistry of element 105 whose half-life is only 35 seconds. Her team also confirmed the discovery of element 106 in 1993. This allowed the 1974 discoverers to propose the name “seaborgium” for element 106 which was approved by the International Union of Pure & Applied Chemistry (IUPAC) in 1997. Between 1996 and 2002 she and her group participated in international collaborations both at Berkeley and in Europe to perform the first studies of the chemical properties of elements 106, 107, and 108. These studies showed the proper placement of these very short-lived elements in the periodic table of the elements.”
Excerpts from Interview with Dr. Hoffman:
Darleane Hoffman: “And one of the required courses you had to take was freshman chemistry. And that was taught by a marvelous woman, Professor Nelly Naylor, whom I later corresponded with. At the time all I knew was that she was an incredibly good teacher and that chemistry appealed to me more than anything else I was taking at the time. So after two quarters of chemistry, and two quarters of applied art, I decided, A, I had no talent for applied art and B, chemistry — or maybe I should have put that as A — chemistry was the thing I really liked and wanted to continue to study. And I have to say it was primarily because professor Naylor was such and inspiring teacher. And chemistry seemed so beautifully logical. But also she pointed out the applications of the chemistry we were learning and how chemistry was a part of everyday life in all respects. And I think she really was way ahead of her time in teaching, because now in recent years we again are trying to point out the applications of chemistry when we’re trying to teach it to beginning chemistry students. So anyway, I decided to switch to chemistry and when I told my applied art teacher who was also my advisor, my freshman advisor. She said, ‘Well, do you think chemistry is a suitable profession for a woman?’, which I thought was a strange comment coming from her as a woman professor. And I said, of course, because my chemistry professor was a woman.”