National Medal of Science Winners

Nuclear Chemist Darleane Hoffman and Atmospheric Chemist Harold Johnston

by Robert Sanders

Atmospheric chemist Harold S. Johnston and nuclear chemist Darleane C. Hoffman, Berkeley professors and researchers at Lawrence Berkeley National Laboratory, are among nine winners of the prestigious National Medal of Science announced April 30 by the White House and the National Science Foundation.

The two chemists will receive the medal later this year during a ceremony at the White House, along with the other recipients of the Medal of Science and recipients of the National Medal of Technology.

  The two chemists will receive the medal later this year during a ceremony at the White House.

Johnston, 76, professor emeritus of chemistry, was among the first to sound the alarm in the 1970s that human activities can harm the Earth's atmosphere.

His scientific concerns about the effects of man-made chemicals on the ozone layer, heatedly attacked at the time, have been borne out by the subsequent discovery of ozone holes over the Earth's poles.

Hoffman, 70, a professor in the graduate school at Berkeley and a faculty senior scientist at LBNL, is internationally recognized for her studies of the chemistry of very heavy elements - most recently the heaviest elements known, 104, 105 and 106.

The National Medal of Science, established by Congress in 1959 and administered by the National Science Foundation, honors individuals who have made a major impact on the present state of knowledge in the fields of physical, biological, mathematical, engineering or social and behavioral sciences. Since it was first awarded in 1962, 22 Berkeley faculty members have received the medal.

Johnston's research concerned the chemical reactions that take place in a mixture of gases, and also how light affects these reactions. In particular he looked at oxides of nitrogen-referred to as NOx, the major constituents of smog-as well as ozone, fluorine, chlorine and various highly reactive free radicals.

His work on NOx reactions first led him to question a proposal of the late 1960s that the country build a fleet of supersonic transport planes to fly in the stratosphere.

His calculations in 1971 indicated that NOx spewed into the stratosphere from the airplanes' exhaust could reduce global ozone by 3 to 23 percent.

Following publication of his findings and the associated publicity, Congress set up its first major program of stratospheric research.

From this beginning came warnings about other ozone destroyers including chlorofluorocarbons, which have since been banned in the United States and many other countries.

As a result the SST fell by the wayside, partly because of economic concerns. In 1982 the Federal Aviation Agency awarded Johnston its citation for "Service in Aviation" for his work on high altitude aircraft pollution.

Johnston is a pioneer in chemical kinetics as well as environmental science. He is the author of a book on gas phase reactions and has published 160 research papers.

Hoffman has devoted her career to the so-called transuranic elements-chemical elements heavier than uranium that typically decay to lighter elements in seconds to milliseconds.

Among these is element 106, the heaviest element discovered so far and recently named seaborgium after the Nobel Prize-winning chemist Glenn T. Seaborg, her long-time colleague.

In 1993 she was among the researchers who confirmed the existence of the element.

"She has been a pioneer in the nuclear chemistry of the transuranic elements since the early 1950s. This is a well-deserved honor," said Seaborg.

Before coming to Berkeley, Hoffman spent 31 years (1953-1984) at Los Alamos National Laboratory. From its inception in 1991 until she retired last year, Hoffman directed the Glenn T. Seaborg Institute for Transactinium Science.

She currently is involved in an international collaboration to study the chemistry of elements 104 (rutherfordium), 105 (hahnium) and 106 (seaborgium), using "atom-at-a-time" techniques that she and her colleagues developed.



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