How has he transformed the scene?
When Alfred Nier graduated from St. Paul's Humboldt High School 1927, he could not in his wildest dreams have imagined the career that lay before him: that he would one day design scientific instruments to accompany spacecraft landing on Mars; that his research on isotopic composition of the elements would provide the basis for more accurate assessments of the Earth's age; that he would be called upon in a future war—the war after "the war to end all wars"— to perform the first uranium isotope separation in history using a mass spectrometer of his own design and making; that in so doing, he would provide the first evidence of the isotope responsible for slow neutron fission (U235) and thus influence the course of history. Young Alfred could not have foreseen that the name Nier would become part of the lexicon of physics: linked to scientific instrumentation, theory, methodology, and exquisitely executed research that revolutionized many disciplines and helped launch whole new fields of study.
Alfred "Al" Nier was just sixteen when he enrolled at the University of Minnesota with the intent of becoming an electrical engineer. But the Great Depression intervened, and with few job prospects upon completion of his undergraduate degree, Nier went on to complete his MS in Electrical Engineering followed by a Ph.D. in Physics in 1936. Nier's introduction to mass spectrometry came in the lab of his graduate study advisor, the highly respected physicist John Tate, whose team was using the instrument for electron impact phenomena. Nier carved out his own territory, electing to focus his doctoral thesis on investigation of the elements and their constituent isotopes with the use of mass spectrometry. It was a specialty that would come to define his career and in many respects, his life.
"One of the things you have to remember is that there were only a handful of people in the entire world who had ever worked or even seen a mass spectrometer, so it was kind of a wide open field…I said, well, this instrument that I have has got such beautiful performance. Why don't I see what I can with isotopes? Because at that time, isotopes had just been discovered, and there was a lot of uncertainty about the relative abundances and around rare isotopes existing, so this instrument lent itself just beautifully to this problem."
Nier, in oral history interview with Konrad Mauersberger, Dec. 7, 1991
Mass spectrometers have been loosely compared to prisms. Whereas a prism separates visible light into its component wavelengths, a mass spectrometer separates the components of a sample material (converted to ionized particles) on the basis of varying mass, as measured by weight. The resulting mass spectrum may reveal, among other things, the existence, identity, abundance, structure, and chemical properties of atoms and molecules present in the sample. In the hands of Alfred Nier, the instrument would perform as never before, revealing clues in the smallest of particles that could answer some of the largest of questions posed by modern science.
As Nier entered the physics arena at the U of MN in his early twenties, mass spectrometry was in many respects an emerging technology, and he found his electrical engineering training to be an important asset. Expanding upon the work of his predecessors, he introduced what have been called "deceptively simple" but were, in fact, profound design changes: constructing mass spectrometers that provided better performance, better resolution, and better stability than other instruments in existence at the time. In so doing, he not only advanced the potential of his own research, he increased the capabilities of scientists around the world.
The improvements opened the door to a host of applications in subject areas ranging from medicine to space science. Equally important, this more powerful tool could be used to re-examine the basic building blocks of matter—atoms, as expressed in the elements and their isotopes—with unprecedented precision and speed. Some of Nier's earliest forays into the periodic table produced exciting results, including the discovery—before he had even completed his PhD—of a new isotope of potassium (K40) and the first quantitative measurements of the isotopes of argon.
Nier received a 2-year post-doctoral National Research Council fellowship to work with Kenneth Bainbridge at Harvard, where he constructed a high resolution mass spectrometer and determined the isotopic composition of nineteen elements, in the process discovering four new isotopes (36S, 46Ca, 48Ca,186Os). Of particular note were his findings on the variations of common lead and the isotopic composition of uranium, which together advanced the field of geochronology by offering a new conceptual basis for determining the Earth's age. Together with colleagues, he also made the surprising determination that the ratio of carbon isotopes 12C and 13C varied in nature and were not constant as had been believed, thus laying the foundation for modern geochemistry.
Despite an offer to stay on at Harvard following his fellowship, in 1938 he returned to the University of Minnesota to accept an assistant professorship in the Physics Department. For the next 56 years he retained his affiliation with the University, mentoring the next generation of scientists, further developing the capabilities of mass spectrometry instrumentation, and conducting his own research. He would rise through the ranks to full professorship, then Chairman of the School of Physics and Astronomy, then Regents Professor of Physics. He retired from the faculty in 1980 but continued to maintain an office and lab, pursuing research interests as Regents Professor Emeritus.
Throughout his more than half-century tenure, Nier helped to build the reputation of the University of Minnesota for scientific excellence of the highest caliber, driven by his own insatiable curiosity and by the unfolding events of the era.
"For all practical purposes, we were in the war before December 7, 1941."
Nier, in 1989 oral history interview with Michael Grayson and Thomas Krick
When nuclear fission was discovered by Berlin scientists in 1938—and its chain reaction potential came to be understood—Nier was caught up in the resulting swirl of activity in the international scientific community. How might the power of fission be harnessed, to what end, and by whom? The potential for use in weaponry was clear.
Although the United States was still years from official entry into WWII, in 1939, at the urging of Albert Einstein and others, President Franklin Roosevelt established a scientific committee to undertake the so-called "uranium project." At the time, Nier's lab at the University of Minnesota was the only one in the world with both the instrumentation and expertise to conduct a separation of the isotopes of uranium. Accordingly, in 1940, he was called upon by Enrico Fermi to perform the first-ever separation of 235U and 238U. Nier famously sent his resulting samples (their weights expressed in nanograms) via U.S. mail to the lab of John Dunning, a colleague of Fermi's at Columbia University. It had been theorized, but now they had their proof: 235U was indeed the isotope responsible for slow neutron fission.
"After Pearl Harbor, he (John Tate) said, "Look, you're not going to be doing anything normal for the next few years."
Nier, in 1989 oral history interview with Michael Grayson and Thomas Krick
Nier's involvement in the wartime applications of mass spectrometry intensified after the bombing of Pearl Harbor, when the uranium project was reframed as the military Manhattan Project. Much of his work in his University of Minnesota lab became classified, as he built mass spectrometers for distribution to other labs and conducted analyses to monitor the results of other scientists running trials on uranium separation methods.
Although he was among the top physicists invited by Oppenheimer to consult on development of the atomic bomb at Los Alamos, Nier believed that his best contribution could be made in the effort to produce sufficient enriched uranium. In the years 1943-45, he relocated to New York City and set up an instrument development lab within Kellex—the corporation charged with building the primary gas diffusion plant for uranium enrichment at Oak Ridge, Tennessee. Among the instruments Nier designed was a helium leak detector that proved vital to the war effort by increasing the speed, safety, and efficiency of the plant's operation. Like many of the 130,000+ people employed in the Manhattan Project, Nier returned home in autumn of 1945, relieved at the war's end but sobered by the power of what had been wrought and its human cost.
"I started flying (rocket flights) in about 1960. I decided, Gee, this is the space age that's coming along, we ought to get into that. And so the problem of studying the composition of the upper atmosphere was an interesting challenge. So I thought, "With all of the experience we have, we ought to build mass spectrometers to do this." And so we built miniature instruments."
Nier, in 1989 oral history interview with Michael Grayson and Thomas Krick
Returning to the University of Minnesota and a full professorship, Nier resumed his teaching schedule and vigorous research agenda. He turned his lab's attention to basic science, among other pursuits conducting remarkable precision mass work that enabled the identification of molecules from their exact molecular weight. In the following decades he collaborated with colleagues and students on research topics of a breadth almost beyond belief. He separated isotopes with a thermal diffusion column, and supported the research of his colleagues in the biological sciences by enriching carbon for use in tracer studies; devised the potassium/argon method of geological dating; analyzed noble gases produced by cosmic rays in meteors; designed new instrumentation such as the sector magnet mass spectrometer and double-focusing mass spectrometer; used miniature rocket-mounted mass spectrometers to obtain the first reliable data on the composition, velocity, and thermal profiles of ions and molecules in Earth's upper atmosphere; was a key figure in the International Commission on Atomic Weights and the adoption of the unified carbon-12 standard; and was engaged by NASA to adapt mass spectrometry instrumentation for the 1976 Viking Mars mission (resulting in detection of argon and nitrogen in the Martian atmosphere). In 1991—some eleven years into his "retirement"—he was studying the isotopes of neon and helium (in particular, the 3H/4H ratio) for clues to the origin of interplanetary dust particles collected from the stratosphere by the U-2 airplanes once used as spy planes.
"…You try to untangle all of these processes to get at the primordial ratio of the heliums in the cosmic dust—it tells you what the solar system was like 5 billion years ago."
Nier, in 1989 oral history interview with Michael Grayson and Thomas Krick
Nier's 218th and final paper was published in the year of his death in 1994, on the subject of noble gases in lunar dust grains. He was just shy of his 83rd birthday, and still peering with interest into the cosmos.
It would take a physicist to fully comprehend the significance of Nier's contributions. But even non-scholars will be inspired by the more worthy accounting of his work—and his numerous collaborators—available in the biographic memoir of Nier written by John Reynolds for the Academy of Sciences Press, and the remarkable transcript of his 1989 interview with Michael Grayson and Thomas Krick at the University of Minnesota (see selected resources).
No one who speaks of Alfred Nier would fail to remark on his character, for he was known for making life-long friends of his colleagues and collaborators around the world. In the often competitive world of science, he was quick to remark on the elegance of a fellow-scientist's research, to give credit where it was due (whether to his predecessors, advisors, grad students, collaborators, or—especially—the machinists from the shop who helped construct his instruments); to say "we" rather than "I" when speaking of landmark discoveries; to voice his admiration for the accomplishments of others who endeavored, as he did, to better understand the primordial character and nature of the universe. Nier's speeches and writings are sparked by words such as "marvelous," and "wonderful" and "beautiful," and references to colleagues as "my dear friend." He was known for his sense of humor and a certain gentle humility, downplaying his own role in successful outcomes with a smile and a shrug, saying, "Being born at the right time helped."
Those who knew him personally counted themselves as fortunate. But those who did not are still fortunate, in that Alfred Nier left a remarkable legacy available to all, in his body of work, in his expansive nature, and in his fine spirit of discovery, which—unlike the meteors he studied—remain undiminished by travel and time. Nier's value is simply beyond measure, no matter how precise the instrument.
