Howard Ecker, Ray Hopper, and Alfred O.C. Nier examine a 60 degrees mass spectrometer that was the prototype for the Consolidated-Nier commercial instrument. Photograph courtesy of the University of Minnesota Archives, University of Minnesota - Twin Cities.
But Nier’s mass-spectrometry work during the Manhattan Project was not just relegated to identifying and regulating uranium separation. He also designed a portable helium-leak detector for use in the gaseous-diffusion plant in Oak Ridge, Tennessee, which proved important. With diffusion being the primary method of uranium enrichment, certain measures had to be put in place to ensure the process worked efficiently with problems detected immediately: during the war any problem or loss in efficiency was deemed critical. Mass spectrometers as designed by Nier came to the rescue here too:
Because of the pumping, the UF6 got hot so you had to have all kinds of refrigeration equipment to cool the gases. Also because of the size and complexity of the plant you had miles of welded joints. Then the question came up, “How can you find leaks if you’re going to have miles of welded pipes and joints and couplings?” There must have been—maybe a million joints is too many, but the number of joints that had to be welded was way, way up in the tens or hundreds of thousands. So how do you test all this stuff? Well, you had to find some way to do it. You could use the usual stunt—you could pump down and have an ionization gauge and read the pressure; or you let it stand and watch the pressure rise with a bourdon gauge. Well, these were all far too crude. So in kicking this around, and I don’t know exactly whose idea it was, but in one of many brain-storming sessions the question came up, “Could you use a mass spectrometer as a leak detector? [...] In practice you used the leak detector as a sophisticated ionization gauge. You tuned it to helium. There isn’t much helium in the air and you could sniff around with helium. Well, at the time, we were building the hydrogen instruments, which were for light masses. So it was simple for us to adopt a hydrogen instrument for the purpose. In a month or so we threw together a portable instrument that could do analysis. (Nier, 102)
Nier’s ideas and discussion with colleagues brought about his invention of the leak detector.
Everybody was concerned; how can we help K-25—that was the name of the plant, K-25. How can we help K-25? The feeling was they had to have many hundreds of helium leak detectors. GE had the contract, a blanket contract for instruments of that kind. So they got the contract for building helium leak detectors. Now before that, they had received the contract for building uranium-analysis mass spectrometers. I should have mentioned that, after we built those first ones, one of the seven we built went to GE as a prototype. (Nier, 103)
During the Manhattan Project, Nier worked alongside other innovators in early mass spectrometry, including Kenneth Bainbridge of Harvard University. Bainbridge went to work as head of the instrumentation-development section of the Manhattan Project; he later worked on test preparation for the atomic bomb. Bainbridge’s efforts played a large role in the success of early testing of the bomb, including the first U.S. test of atomic weapons, the Trinity Test. Nier’s work also provided building blocks for other larger efforts and more elaborate instruments during the war. Ernest Lawrence, a physicist working out of the University of California, Berkeley, saw the need for a bigger, better mass spectrometer—one that could be used to analyze substantially larger known quantities of isotopes than the models available at the time. Lawrence thus invented the calutron, which he manufactured for isotope-separation plants at Oak Ridge. The calutron method of separation was used in conjunction with the gaseous-diffusion method and was especially necessary in the period before the gaseous-diffusion procedure reached its design goals.
Nier was not the only mass spectrometrist to work on the atomic bomb. The project required many individuals in physics, chemistry, and engineering, and Seymour Meyerson was part of the Manhattan Engineer District, the division of the Manhattan Project created by the army to accommodate engineering work. Meyerson recalls, “Now, in the laboratory at the pilot plant that was operated where I spent my time, there was the first mass spectrometer that I ever met face to face. [...] This was 1944 or 1945; 1944 I would guess” (Meyerson, 7). Meyerson’s work, like the work of so many others involved in the bomb, was classified. The project was, obviously, shrouded in secrecy, and that secrecy extended even to staff:
Hear Seymour Meyerson: In any case, I recall vividly that even the technical people on that project had essentially no information. They were given no information, except the technical aspects of their particular job there. [...] At least formally, they had no idea. Obviously, people did a lot of speculating, and several of the technical people had a pretty good notion of what it was all aimed at, what it was part of. But they were not encouraged to talk about their speculations. (Meyerson, 9)
After the War mass spectrometers became commercially available. A page from the manual for the CEC Type 21-104 Mass Spectrometer. CHF Collections. Click here for full size.
Meyerson at least knew he was using a mass spectrometer to monitor isotopic composition, but the instrument was mysterious in many ways. It was part of classified work, which limited the number of people who knew about its existence and use within the work on the atomic bomb. And the instrument itself was new to chemists like Meyerson; so its capabilities had not been fully explored. Meyerson’s work with the mass spectrometer was a precursor to a postwar career at Standard Oil Company, where the mass spectrometer became an integral part of his research. In fact, the mass spectrometer was quickly becoming an integral part of many areas of chemistry and physics research.
War’s End, Mass Spectrometry’s Foundation
World War II demonstrated the utility and problem-solving ability of science, with mass spectrometry among the useful new techniques. In the Manhattan Project mass spectrometry had solved a definable problem: how to measure and identify uranium isotopes, which was no small task in and of itself. In doing so, it also developed into a serious tool not only of physicists but of chemists as well.
The war’s science boom had yet another lasting impact on mass spectrometry: the heavily leaned-upon petroleum industries developed new processes for handling the pressures of wartime research, and those new, often complicated processes required just the kind of analysis that a mass spectrometer could provide. Concurrently with the Manhattan Project, the mass spectrometer was making inroads in the petroleum and chemical industries. Unsurprisingly, the technology of mass spectrometry had advanced rapidly during the war with focused and increased use. Increased demand for fast analyses and better instrumentation led to a rising desire for the previously unknown and mysterious field of mass spectrometry. And without the analysis of such minute things as isotopes that mass spectrometry could provide, something so massive as the bomb would not have become a reality.