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Dr. Alfred O. C. Nier


(1911 - 1994) Minnesota born and educated, Dr. Nier is the states most renowned physicist. His specialty was instrumentation and he had a unique talent for developing sophisticated instruments to do science. In the 1930s, he was the only scientist in the world who could build and use a mass spectrometer, a device that weighs atoms. Each type of atom has its own particular weight, so the spectrometers that Nier built in the basement of the University’s physics building gave him a unique window on the atomic world. As the world authority in weighting atoms with his ingenious mass spectrometer, he measured the masses of most of the elements of the periodic table and discovered the isotopes of potassium, sulfur, calcium, osmium and other elements.

While studying at Harvard, he became interested in applying mass spectrometry to the measurement of geological age. In 1938, while still in his 20s, he used a mass spectrometer to measure the isotopes of lead, which allowed him to determine the age of the Earth. His work, extended by others, led to our present knowledge that the solar system is around 4.5 billion years old rather than 2.0 billion as previously thought.

Nier’s most famous, and fateful, discovery came in 1940, just four years after he had received a doctorate in physics from the University of Minnesota. He was asked by scientists with the Manhattan Project, the code name for the atomic bomb effort, to determine which of two isotopes of uranium was capable of sustaining a nuclear reaction. He was the first to separate the radioactive isotopes uranium-238 and uranium-235. Using a mass spectrometer of his own design, he performed a key experiment showing that uranium-235 could be made into an atomic bomb, then taped the results in the form of two small spectrometer targets to the margin of a letter he sent to the other scientists. His discoveries proved to be of critical importance in unleashing the power of the atom, and a major contribution to the development of the atomic bomb and the launching of the atomic age. He also helped develop mass spectrometers and helium-leak detectors that were instrumental in the success of the Manhattan Project.

He helped design miniature mass spectrometers that could be launched by rockets to study the Earth’s atmosphere, and he led a group that determined the composition of the thermosphere, the part of the upper atmosphere in which the temperature increases continuously with altitude.

In the 1970s, Nier again came to the scientific forefront when he was one of 38 American scientists asked by NASA to work on the Viking mission to Mars. He headed NASA’s entry science team and helped devise experiments and design equipment for the Mars landing. He designed compact instrumentation used to determine the atmospheric elements on Mars. He also analyzed data from the 1976 Viking landing on the planet, which demonstrated that the Martian atmosphere could not support life as we know it. At the time of his death he was overseeing a NASA-financed project to determine the composition and origin of cosmic dust.

His research extended into the fields of geology, chemistry, biology, medicine and astronomy. Besides holding many patents, Nier authored or co-authored over 150 publications. During his long career, Nier received many honors, including over 30 honorary awards and doctorates, and election to the prestigious National Academy of Sciences. Several of his colleagues believe his work was worthy of a Nobel Prize. They say his decision to leave Harvard University in 1938 to accept a position at his alma mater, the University of Minnesota, cost him the highest prize in science. Widely regarded as the best physicist who ever worked there, he is the first to hold the distinctive title of Regents Professor of Physics at the University of Minnesota.

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