On May 28, 1911, American physicist Alfred Otto Carl Nier was born. Nier pioneered the development of mass spectrometry. He was the first to use mass spectrometry to isolate uranium-235 which was used to demonstrate that 235U could undergo fission and developed the sector mass spectrometer configuration now known as Nier-Johnson geometry.
Alfred Otto Carl Nier attended the University of Minnesota and graduated in electrical engineering in 1931. Nier decided to continue his graduate studies in physics. In 1936, Alfred Nier won, due to his skills on spectroscopy, a fellowship at Harvard University. Two years later, he published measurements of the relative abundance of the isotopes of uranium, measurements that were used by Fritz Houtermans and Arthur Holmes in the 1940s to estimate the age of the Earth.
For mass spectrometry, the molecules to be investigated are transferred into the gas phase (desorption) and ionized. The ions are then accelerated by an electric field and fed to the analyzer, which “sorts” them according to their mass-to-charge ratio, for example spatially into partial beams as in a sector field mass spectrometer. The molecules can be fragmented. Fragmentation is often desired, especially with comparatively complex biopolymers, since the fragments are more easily transferred into the gas phase, for example in the investigation of proteins. Mass spectrometry is used in many areas. It is used in characterization of chemical compounds, in biochemistry for the investigation of biomolecules, in medical chemistry for the identification of substances in body fluids or organs, in forensic investigations, in doping controls, in environmental analysis, in the analysis of chemical warfare agents and explosives.
Alfred Nier moved back to Minnesota in 1938 in order to be closer to his parents. However, two years later Enrico Fermi requested Nier and a few students to prepare a pure sample of uranium-235 using an early mass spectrograph designed by Nier, for John R. Dunning‘s team at Columbia University. It was then sent by US Postal Mail to Dunning’s team. They were then able to show that U-235 was the isotope responsible for nuclear fission, rather than the more abundant uranium-238. This achievement is considered a critical step in the development of the atomic bomb. During World War II, Alfred Nier and the Kellex Corporation in New York City researched on the design and development of efficient and effective mass spectrographs for use in the Manhattan Project to build the atomic bomb in the war.
After World War II, Nier returned to Minnesota where he worked on geochronology, the upper atmosphere, space science and noble gases. He further designed the miniature mass spectrometers used by the Viking Landers to sample the atmosphere of Mars. Alfred Nier became a member of the National Academy of Sciences as well as a foreign scientific member of the Max Planck Society. The Nier Prize is awarded annually by the Meteoritical Society and recognizes outstanding research in meteoritics and closely allied fields by young scientists.
References and Further Reading:
-  Alfred Nier, 82; Physicist Helped Foster A-Bomb at the NY Times
-  Alfred Nier Interview at Voices of the Manhattan Project
-  Alfred Nier at the National Academy of Sciences
-  Arthur Holmes and the Age of the Earth, SciHi Blog
-  Viking 1 and the Mission to Mars, SciHi Blog
-  Alfred Nier at Wikidata