Cryogenic Engineering by Russell B. Scott [1] was written between 1955 and 1959 as a text book, reference book, and data book. It covered liquefaction and separation of gases; thermometry; instrumentation; thermal insulation; storage, transport, and transfer of liquids; and properties of fluids and solids. It contains the best detailed description of the liquefier project that was conducted in the early 1950s at the NBS Boulder Laboratories. The book has been reprinted several times, most recently in 1995, and more than 6000 copies have been sold.

The NBS cryogenics program started in 1904 when Congress appropriated funds to purchase the two-literper-hour hydrogen liquefier exhibited at the St. Louis World's Fair by the British Oxygen Company. It was rarely used until 1925, when F. G. Brickwedde, and later Russell Scott, started producing liquid hydrogen for research and as a coolant to liquefy helium. In the early 1930s, Harold C. Urey of Columbia University set out to prove experimentally the existence of an isotope of hydrogen which we now call deuterium. As described elsewhere in this volume, he asked Brickwedde to liquefy hydrogen and, by distillation, to concentrate isotopes for spectroscopic analysis. Urey found deuterium present in the sample [2] and was awarded the Nobel Prize. In 1934, Scott, Brickwedde, Urey, and Wahl [3] published the hydrogen ortho/para uncatalysized conversion rates, and in 1948, Woolly, Scott, and Brickwedde [4] published a compilation and critical evaluation of the thermal properties of the isotopes of hydrogen.

In the 1940s, the emphasis in the field of cryogenics changed dramatically from research to engineering, which stimulated great improvements in system performance. Some of the engineering applications that evolved over the next decades included storage and shipment of gases such as oxygen, nitrogen, hydrogen, helium, and natural gas in liquid form; production of oxygen for making steel; rocket and aircraft fuels; energy transport and storage; electronics; and facilities for high-energy physics. NBS was one of the few U.S. laboratories with equipment, personnel, and experience to meet the national need for information and data.

During World War II, Brickwedde and Scott participated in the Manhattan Project [5], measuring the thermodynamic properties of materials used in the atomic bomb, including uranium. After the war,

Brickwedde became a consultant on cryogenics at the Los Alamos Scientific Laboratory (LASL), working with Edward Hammel and members of the LASL cryogenic group. NBS Director Edward U. Condon, who had played a part in the work at Los Alamos during the war, wanted to expand NBS research in atomic and nuclear physics and encouraged Brickwedde to facilitate collaboration with LASL.

When President Truman authorized the design and testing of a hydrogen bomb in 1950 to counter a threat from the Soviet Union, the U.S. Atomic Energy Commission, through LASL Director Norris Bradbury, asked NBS to participate. He requested that NBS build a large hydrogen-liquefaction plant; set up and run a hydrogen/deuterium electrolysis plant; test prototype dewars for Los Alamos; assist MIT and Arthur D. Little Company (ADL) in the design and construction of dewars and refrigerators; test hydrogen transport dewars; and train personnel in large-scale hydrogen production and hydrogen handling.

Russell Scott, assisted by William Gifford, Victor Johnson, and Dudley Chelton, designed and built the critical components (heat exchangers and gas purifiers) for four 320 L/h hydrogen/deuterium liquefiers in the NBS shops in Washington. The NBS staff quickly expanded to include Bascom Birmingham, Richard Kropschot, Douglas Mann, Robert Powell, Robert Jacobs, Leon Wagner, and Peter Vander Arend. In 1950, the City of Boulder gave NBS a 28-acre site for relocation of the Central Radio Propagation Laboratory and, later, other NBS units from Washington. Under NBS direction, Stearns Roger Engineering erected two of the liquefiers in Boulder. The third liquefier was erected by Holmes and Narver on the Eniwetok Atoll, site of an upcoming nuclear test, under the direction of Herrick Johnston of Ohio State University, with assistance from George Freeman and Leon Wagner of NBS. The fourth liquefier was used for spare parts.

In order to obtain deuterium, two water electrolyzers were installed in Boulder, heavy water was imported from Canada, and work was begun to produce deuterium gas needed for the upcoming nuclear test. The deuterium was compressed into high-pressure tanks and shipped to the atomic proving station on Eniwetok in the Marshall Islands where it was condensed using the NBS liquefier.

The thermonuclear device was designed at Los Alamos [6]. Liquid hydrogen used to test the components was safely transported from where it was produced in Boulder to Los Alamos in dewars designed and built by the Cambridge Corporation. Because of program priorities, the Cambridge Corporation and LASL took on the primary responsibility for the design and testing of the dewars. In March and April 1952, Herrick Johnston and his staff visited Boulder to participate in liquefier operation as part of the preparation for assembling and operating the liquefier on Eniwetok. On November 1, 1952, the Eniwetok Atoll was evacuated of all personnel, and the "ivy MIKE" shot was detonated. It was the first hydrogen thermonuclear device and was regarded as extremely successful, yielding 10.4 megatons of TNT equivalent and providing scientific data for future tests and development of weapons. The liquefier described in Scott's book played a critical role in the success of this test.

In 1953, the NBS staff (Brickwedde, Scott, Baird, Birmingham, Chelton, Freeman, Gifford, Goddard, Johnson, Kropschot, Powell, and Vander Arend) were

awarded the Department of Commerce Gold Medal for "The design, construction and operation of large and unique hydrogen and nitrogen liquefiers."

As the need for cryogenics in nuclear testing diminished, the NBS cryogenics facilities, led by Russell Scott, turned attention to a growing national need for scientists and engineers to be trained in cryogenics, as well as to the measurement and collection of very low temperature data. Scott organized the Boulder staff into discipline-oriented groups to provide the data necessary for cryogenic design. These groups included Thermodynamic Properties of Cryogenic Fluids; Mechanical and Thermal Properties of Solids; Instrumentation (thermometry, liquid level, pressure); Systems (liquefaction and refrigeration, fluid flow, dewar design, distillation); Data Center (compilation, critical evaluation and dissemination of data); and Production of Cryogenic Fluids (hydrogen, helium, nitrogen).

Scott was committed to on-going training, and in 1954 he initiated the first Cryogenic Engineering Conference (CEC) in Boulder, which attracted more than 400 participants. The technical papers were

published in the first volume of Advances in Cryogenic Engineering (ACE). Since then there have been a total of 40 CEC conferences with commensurate ACE publications involving an estimated 25,000 participants.

An entire generation of engineers and scientists has used Scott's Cryogenic Engineering, which not only outlines fundamentals, but also includes detailed design principles and techniques. It was the first of its kind and is still considered an important reference today. The book begins with a description of how fluids are liquefied and gas mixtures are separated. The examples illustrate the basics of design and operation for all types of cryogenic equipment. Thermometry is fundamental to all of cryogenics. The book includes a discussion of temperature scales and temperature measurements, as well as guidance on how to avoid common errors when making these measurements. It continues with a discussion of representative technology including heat exchangers, valves, transfer lines, expansion engines, and insulation technology-since once gases are liquefied, they are ready for transfer, storage, and transport. Both tables and graphs are used to illustrate typical thermal insulations. The small heats of vaporization coupled with relatively large temperature differences warrant sophisticated insulations. These insulations almost always require double-walled high vacuum designs. The vacuum space is often filled with

low-density powder or multilayers of radiation-reflecting material. The thermodynamic properties of cryogenic fluids-helium, hydrogen, neon, nitrogen, and oxygen-are presented graphically. The book also includes data on the thermal and mechanical properties of some of the more widely used structural materials. Each chapter cites references to handbooks and review articles that are fundamental to cryogenic research. In the preface, Scott acknowledged the assistance of NBS staff members who contributed to the preparation of the book and who helped establish NBS as a world-class research facility and a national resource.

In 1960, Scott was invited by the director of the UCLA Engineering Extension Division to teach a twoweek short course using Cryogenic Engineering as the text. Assisted by R. H. Kropschot, Scott presented his first course in December 1960. The UCLA course was taught annually for more than 35 years by a variety of instructors from the NBS Boulder Laboratories. Other courses followed in Boulder, at various NASA facilities, universities, National Laboratories, and other institutions. Over the years, an estimated 5,000 students have taken these NBS-initiated short courses. In 1967, Scott received the Department of Commerce Gold Medal for Exceptional Service for "Exceptional Leadership and Meritorious Authorship in the Development of Cryogenic Engineering."

Scott's legacy is more than a book and the organization that he helped to build at NBS. Members of his staff participated in all the major U.S. cryogenic engineering programs for more than 25 years. Some examples of his legacy may be mentioned. In his Nobel acceptance speech, Luis Alvarez (University of California, Berkeley) acknowledged the work of Chelton, Mann, and Birmingham for design contributions to the Lawrence Berkeley Laboratory hydrogen bubble chamber. NBS programs funded by NASA supported Centaur, the first hydrogen/oxygen space vehicle; storage of hydrogen and oxygen for fuel cells and breathing oxygen; hydrogen/oxygen safety; fluid and solid properties; instrumentation; and fluid flow. Measurements, compilation, and critical evaluation of the thermodynamic properties of fluids by NBS scientists (Corruccini, Goodwin, McCarty, Strobridge, Roder, Diller, Weber, and Younglove) have fulfilled governmental and industrial requirements for engineering design. They assisted in the design and construction of the NASA hydrogen liquefiers (the Bear Plants-Baby, Mama, and Papa); design of high energy physics accelerators and detectors; and the formulation of LNG safety procedures. A data book describing safety regulations and thermodynamic properties [7] was developed for the liquefiednatural-gas (LNG) industry. And finally, one of Scott's legacies most often cited is that of technology transfer, which has had a wide impact as former NBS employees move into new positions in industry and academia.

Russell B. Scott was born in Ludlow, Kentucky, on April 17, 1902. He received his B.S. (1926) and M.S. (1928) in physics from the University of Kentucky and joined NBS immediately afterward. He was Director of the Boulder Cryogenics Laboratory from 1952 to 1962 and Director of NBS Boulder Laboratories from 1962 to 1965. He died September 24, 1967 in Boulder.

Prepared by Richard H. Kropschot.

Bibliography

[1] Russell B. Scott, Cryogenic Engineering, D. Van Nostrand Co., Princeton, New Jersey (1959); reprinted Oct. 1959, Aug. 1960, May 1962, and in 1995.

[2] H. C. Urey, F. G. Brickwedde, and G. M. Murphy, A Hydrogen Isotope of Mass 2, Phys. Rev. 39, 164-165 (1932).

[3] R. B. Scott, F. G. Brickwedde, Harold C. Urey, and M. H. Wahl, The Vapor Pressures and Derived Thermal Properties of Hydrogen and Deuterium, J. Chem. Phys. 2, 454-464 (1934).

[4] Harold W. Woolley, Russell B. Scott, and F. G. Brickwedde, Compilation of Thermal Properties of Hydrogen in Its Various Isotopic and Ortho-Para Modifications, J. Res. Natl. Bur. Stand. 41, 379475 (1948).

[5] Richard Rhodes, The Making of the Atomic Bomb, Simon and Schuster, New York (1986).

[6] Richard Rhodes, Dark Sun: The Making of the Hydrogen Bomb, Simon and Schuster, New York (1995).

[7] Douglas B. Mann, LNG Materials and Fluids: A User's Manual of Property Data in Graphic Format, NBS Cryogenics Division, National Bureau of Standards, Boulder, Colorado (1977).

In late 1956, experiments at the National Bureau of Standards demonstrated that the quantum mechanical law of conservation of parity does not hold in the beta decay of Co nuclei. This result, reported in the paper An experimental test of parity conservation in beta decay [1], together with ensuing experiments on parity conservation in μ-meson decay at Columbia University, shattered a fundamental concept of nuclear physics that had been universally accepted for the previous 30 years. It thus cleared the way for a reconsideration of physical theories, especially those relating to symmetry, and led to new, far-reaching discoveries regarding the nature of matter and the universe. In particular, removal of the restrictions imposed by parity conservation first resolved a serious conflict in the theory of subatomic particles, known at the time as the tau-theta puzzle, and later led to a fuller understanding of the strong, electromagnetic, and weak interactions. The better understanding of their characteristics has led to a more unified theory of the fundamental forces.

The beta-decay experiments were carried out by C. S. Wu of Columbia University in collaboration with NBS staff members Ernest Ambler, Raymond W. Hayward, Dale D. Hoppes, and Ralph P. Hudson. The Bureau's low temperature laboratory was chosen for the experiments because of its millikelvin-region research capability [2] and the staff''s experience in the spatial orientation of atomic nuclei [3], an essential feature of the beta-decay study.

Basically, parity conservation in quantum mechanics means that two physical systems, one of which is a mirror image of the other, must behave in identical fashion. In other words, parity conservation implies that Nature is symmetrical and makes no distinction between right- and left-handed rotations, or between opposite sides of a subatomic particle. Thus, for example, in beta decay there should be no preferential direction of emission with respect to the direction of the spin of the emitting nucleus, i.e., no (nuclear) spin-(electron) momentum correlation.

Since 1925, physicists had accepted the principle that parity is conserved in all types of interactions. During the 1950s, however, phenomena were found in highenergy physics that could not be explained by existing theories. The available accelerators produced a variety of subatomic particles. One such particle is the shortlived K meson emitted in the collision of a high-energy

proton with an atomic nucleus. The K meson seemed to arise in two distinct versions, one decaying into two π mesons, the other decaying into three pions, with the two versions being identical in all other characteristics. A mathematical analysis showed that the two-pion and the three-pion systems have opposite parity; hence, according to the prevalent theory, these two versions of the K meson had to be different particles.

60

Early in 1956, T. D. Lee of Columbia University and C. N. Yang of the Institute for Advanced Study, Princeton University, made a survey [4] of experimental information on the question of parity. They concluded that the evidence then existing neither supported nor refuted parity conservation in the "weak interactions" responsible for the emission of beta particles, K-meson decay, and such. They thus proposed that the K-meson itself may have definite parity, and the observed opposite parity of the two systems of decay products may be the manifestation of parity non-conservation in its decay. They suggested that parity may not be conserved. in weak interactions, saw that there was no experimental evidence that proved that this was or was not true, and proposed a number of experiments that would provide the necessary evidence. One of the proposed experiments, which involved measuring the directional intensity of beta radiation from oriented Co nuclei, seemed to them to be the best prospect for success in testing their hypothesis. Yang and Lee had turned to betaspectroscopist and Columbia University friend and colleague Chien-Shiung Wu for advice on how to pursue their preferred suggestion. Wu, in turn, approached Henry Boorse of Columbia and his close associate Mark W. Zemansky of the City College of New York, who together ran a modest research program in cryophysics at Columbia. Although these scientists lacked the "parity-required" facilities, they were active members in the international low-temperature-physics community, well acquainted with the NBS program and the recent move thereto of Ernest Ambler, a graduate from the Oxford (UK) "cryonuclear physics" research program [5]. It was they who suggested that Wu make initial contact with Ambler and, in fairly short order, arrangements were made to carry out this experiment in the Bureau's low-temperature laboratory.

The envisaged experiment was far from routine and involved many unknowns at the outset. The source of the B-rays would have to be in intimate contact with the