(b. Brooklyn, New York, 21 June 1916; d. Arlington, Virginia, 9 September 2000)
solid-state physics, x-ray diagnostics and radiation detection, solar physics, astrophysics, space science.
Friedman was the first to develop and apply reliable electronic detection devices to the study of the high-energy radiation from the Sun by carrying them into space on a succession of sounding rockets and satellites. His team pioneered x-ray solar astronomy from rockets and became the first to detect x-ray emission from the Sun and were among the first to explore nonsolar x-ray sources in the night sky. He is remembered as one of the founders of x-ray astronomy.
Early Life and Training . Friedman was the second of three children of fine-art framer and dealer Samuel Friedman and Rebecca Seligson and grew up near his birthplace in Brooklyn, New York. His family was of modest means, but even during the Great Depression insisted that Herb get a college education. He therefore entered Brooklyn College choosing art initially, partly because his father had at one time encouraged him to seek out an apprenticeship to an Israeli artist. He spent two years in the major, finally becoming disillusioned about a career, and switched to physics partly because of a fine teacher. This change was acceptable to his family, for whom Albert Einstein was, as Friedman recalls “a folk figure, a hero figure” (Friedman oral history, 2 September 1983, NASM, p. 5).
He came under the direction of the physicist Bernhard Kurrelmeyer, a specialist in photoelectricity, photo-conductivity, and secondary emission phenomena, and who was married to the Columbia University physics professor Lucy Julia Hayner. Friedman graduated in physics in 1936 after spending considerable time in Kurrelmeyer’s laboratory, who then directed him to a student instructorship at the Johns Hopkins University, Kurrelmeyer’s alma mater.
Friedman continued to specialize in laboratory physics, working at first for James Franck, head of the Physics Department and corecipient of the 1925 Nobel Prize in Physics. Franck soon left for the University of Chicago, so Friedman found a place in x-ray spectroscopist Joyce Alvin Bearden’s laboratory and learned how to interpret the detailed signatures of x-ray absorption edges (found at spectral series limits) to determine the binding energies of the electrons in metals and hence explore their structure. Friedman’s task was to develop an improved detector, based upon the classic Geiger counter design, but using thin metallic entrance windows that would admit soft x-rays and then get them to discharge inside an argon gas–filled chamber, producing an electric current that could be measured. Friedman’s photoelectric amplifier circuits consisted of cylindrical metal chambers with a thin wire running on the axis, insulated from the chamber walls. The chambers would be evacuated and then filled with a halogen, typically argon, using alcohol as a quenching agent. An entrance window at the end of the cylinder held a variety of thin metallic windows to admit x-radiation and isolate the tube from other radiations. Its composition and thickness determined the energy threshold desired. After just a few weeks of building and testing these tubes, Friedman found them to be reliable and highly linear detectors of soft x-rays. The metallic windows permitted almost one atmosphere of pressure, which simplified manufacture and ensured high sensitivity.
Employing Bearden’s large double-crystal x-ray spectrometer and his improved detector, Friedman contributed to a better understanding of the nature of a group of metals (from iron to germanium) on the periodic chart known as the transition metals, elements whose second outer atomic levels are not completely filled with electrons. He was able to relate his observations to new theories of the metallic solid state, and received his PhD for this work in 1940. With Bearden he applied his techniques and new detectors to a number of metallic alloys.
At graduation, Friedman hoped to get an industry job and interviewed at both General Electric and at Bell Laboratories, but even though the scientists there were receptive, he never got beyond the personnel offices. So he stayed at Johns Hopkins for another year as an instructor performing contract research under Bearden on electrolytic polishing. Meanwhile the senior Johns Hopkins spectroscopic physicist August Herman Pfund steered Friedman into the civil service sector, where anti-Semitism was less entrenched, and soon found him a job at the Naval Research Laboratory (NRL), which had strong Johns Hopkins connections. Finally permanently employed, Friedman was ready to marry, asking Gertrude Miller, who had been an instructor at Brooklyn College, to be his wife. They raised two sons.
The NRL . Friedman, “elated to get a job,” (Friedman oral history, 2 September 1983, NASM, p. 16) started to work in the Metallurgy Department under Richard Canfield, hoping to apply his thesis knowledge, essentially his expertise at the forefront of the study of the solid state, to stress-analysis problems such as low expansion alloys and high tensile strength alloys that would be useful for things like turbine blades. Canfield soon left, however, and though Friedman worked among Johns Hopkins graduates and found the general atmosphere at the NRL stimulating, he felt he was being constrained to less exciting areas of testing, although he still managed to apply his expertise, developing nondestructive testing techniques using sensors in different sensitivity ranges from Geiger counters and proportional counters to ion chambers.
During his first year in Metallurgy, Friedman responded to wartime orders to develop new and more efficient techniques to manufacture oscillator plates using quartz crystalline plates, an essential ingredient in radio communications gear. The problem was to find a way to orient raw crystals in a cutting machine quickly and accurately. He immediately knew from his x-ray spectroscopy experience that one could rapidly determine crystalline orientation using x-ray diffraction, and it would be far quicker to employ a photoelectric detector than the usual photographic methods. One could orient the crystal in real time, controlling the process by monitoring the Bragg reflections from the crystals, and make the cut then and there. Friedman was able to create a prototype device literally overnight, which impressed the Signal Corps and industry inspectors and led to the immediate production, under Friedman’s direction at NRL, of some two hundred proportional counters for use in industry. In 1945 Friedman was recognized for this work by the U.S. Navy’s Distinguished Civilian Service Award.
But more important, this early achievement gave Friedman increased leverage to apply his techniques and detectors to a wide range of uses. Industry provided him with better facilities at NRL, and so he set about various projects converting all types of detection devices, diagnos tic systems, and maintenance procedures that heretofore used photography or mechanical methods, to employ his high-energy x-ray detectors. He developed electronic analogues for a wide variety of applications including a diffractometer that used x-ray diffraction patterns to improve an antifouling ship-bottom paint formula that would resist the growth of barnacles. With the diffractometer he found that he could discriminate between different copper paint alloys that had very different resistances to barnacles. He also found that his techniques could be used to maintain the consistency of pigments and to determine the minimum amount of silver required to create an efficient electrical contact.
Friedman applied his improved x-ray detectors to a very broad range of applications. His laboratory notebooks during this time attest to his constant search for new uses, from the examination of thin films, x-ray fluorescence analysis, radiation exposure surveys, and ultimately, in the late 1940s, an extensive radiation monitoring system that detected Soviet nuclear tests in 1949.
By the end of the war Friedman was head of an electron-optics branch in the Optics Division of NRL, working directly under Edward O. Hulburt. He made the transition in 1942 when Hulburt set up the new branch, mainly to accommodate Friedman and to grab a new electron microscope that had been slated for the Chemistry Division. The Chemistry Division had balked at taking in Friedman, so Friedman, disgruntled, was well along looking for another job at the National Bureau of Standards when Hulburt made his move. Hulburt acted quickly and effectively setting up the new branch and Friedman spent the rest of the war years developing techniques in x-ray analysis and diagnostics. After the war he continued in radiation detection ranging from electronic aircraft fuel tank gauges to long-range nuclear bomb detection. He directed the development of the navy’s “Project Rainbarrel,” a network of detectors at air weather stations that sensed trace radioactivity in rainwater. When increased radiation was detected, aluminum hydroxide–doped water samples were collected and rushed back to the NRL for precise determination of the spectral signature of the Russian tests.
Research with Rockets . Early in 1946, Friedman and other members of Hulburt’s Optics Division became aware of the possibility of performing research with captured German V-2 rockets. Friedman, however, remained in x-ray analysis, but in July 1947 he was alerted to the fact that his Rainbarrel system had recorded radiation that was linked to a giant solar flare. This was a fascinating coincidence, merely a sidelight at the time, but it sparked an interest in solar phenomena. He had already studied natural radiation sources to calibrate Rainbarrel, but now knew that the Sun could be an x-ray emitter as well. Eventually, Hulburt drew Friedman into the rocket sonde work by 1949. By then, one of the branches led by Richard Tousey had been successful obtaining photographic ultra-violet spectra, but they had still not penetrated down to the high-energy region of the solar spectrum, especially where the source of ionizing radiation in Earth’s upper atmosphere was thought to lurk. Doing this was critical to the navy’s mission because it was thought to be the natural agent governing long-range radio communications.
Once again, Friedman had the ideal detector system. Not only could it reach the extreme-ultraviolet and x-ray regions easily, but it was electronic and so could send its information back to Earth by radio. So Friedman formed a small group within his electron optics branch to build and fly banks of counters on V-2 rockets and soon provided the first observations that led to a detailed understanding of the relative importance of solar ultraviolet and x-ray radiation as ionizing agents upon different layers in Earth’s atmosphere. This new application was especially appealing to Friedman as it was for members of his group, especially Edward Taylor Byram, who had a specific interest in astronomy. The evident success of their first 1949 flight convinced Friedman to move heavily into space research. He recalled not being able to resist it, “because it was just too rich, too exciting” (Friedman oral history, 2 September 1983, NASM, p. 60). He had gained more than enough equity in the navy to pursue this professionally risky work, he felt, and Hulburt was very supportive. Although he recalled this as a watershed time in his life, breaking away from solid-state physics and moving into geophysical and astrophysical areas, in fact much of his electron-optics group remained in the original problem area for some time.
After the V-2s ran out, Friedman’s rocket team continued flying detectors on the navy’s Viking rocket as well as on Aerobees and even smaller balloon/rocket combinations called Rockoons. They performed a wide range of solar observations in the far ultraviolet through the hard x-ray region. In 1952, from an especially ambitious array of detectors they built and flew on a Viking, they obtained data that confirmed the type of radiation that created Earth’s ionospheric E layer. The economical Rockoons became their favored transport system, however, because these vehicles could be launched from shipboard to anywhere over a great range of latitude to study provide geophysical information.
Friedman became a major contributor to x-ray detector and instrumentation development for space research during the late 1950s and 1960s. His team was literally the only one working in the field before Sputnik, and was by far the largest. Among many accomplishments, they found that solar flares emit hard, or extreme high-energy, x-radiation that can produce radio blackouts, and they also used a total solar eclipse to study the spatial structure of x-radiation in the solar corona. They were also the first to successfully image the Sun in x-rays, using a simple pinhole camera design. Starting in 1955, members of his group started performing nighttime stellar ultraviolet observations from Aerobee rockets. In 1958, Friedman became superintendent of a new atmospheric and astrophysics division at the NRL.
Friedman was always dedicated to mentoring and training, and constantly invited graduates and postdoctoral students to assist his team at the NRL. Under his guidance his core team for rocketry, Byram, Talbot Chubb, and Robert Kreplin, guided numerous students. In 1962, Friedman secured funding from the National Science Foundation to establish the E. O. Hulburt Center for Space Research at the NRL, which provided a formal means of mentoring younger professional workers interested in learning the art and craft of the space sciences. In another reorganization in 1963 he was designated superintendent of a new Space Science Division and made chief scientist in the E. O. Hulburt Center for Space Research. He held these positions concurrently until his retirement in 1980.
The Satellite Era . The seniority and equity Friedman enjoyed by the time Sputnik flew and the National Aeronautics and Space Administration (NASA) was formed led him to remain within the navy. NASA had invited him to take the position of chief physicist at the Goddard Space Flight Center, to make the move along with many of his NRL colleagues, but, as he implied in an interview, he was not interested in moving from one administrative position that allowed him to continue research, to another where the personal research option was unknown or unlikely. At least, thinking about those among his colleagues who did leave for NASA, such as Homer Newell, he rationalized their decisions as being promoted by the chance to move up the administrative ladder. He was as far as he wanted to go on that ladder.
Friedman and his staff not only set the stage for scientific research with sounding rockets and then satellites in the 1960s, but they provided a means through which a broader population of workers might gain needed hands-on experience in the complex and demanding technical and organizational enterprise, carrying this experience back into the academic world. Friedman’s team was unparalleled in its ability to devise counters that worked reliably and consistently in the very hostile environment of the payload of a rocket or satellite. They developed both dispersive and nondispersive systems for a wide range of applications, flying them on balloons, sounding rockets, and many navy and NASA satellite missions.
Friedman’s group instrumented the navy’s Solar Radiation Satellite (SOLRAD) series that, first launched in 1960, was dedicated to long-term monitoring of the high-energy radiation from the Sun and could detect local sources of high-energy radiation as well. About a year after the first launch Friedman recalled, he was asked by the President’s Science Advisory Committee (PSAC) to examine SOLRAD monitoring records to see if any anomalous radiation had been detected, as well as to discuss with them the feasibility of monitoring for nuclear tests using satellites. SOLRAD had apparently detected nonsolar sources as “noise,” but their origins remained undetermined and were probably celestial. Nevertheless, SOLRAD showed that it was feasible, which led to the VELA (Spanish for “vigil”) program based at Los Alamos, a program he would have been happy to acquire for the navy.
The great challenge for Friedman in the late 1950s and early 1960s was to adapt his detectors for night operations and to detect nonsolar diffuse and discrete x-ray sources. His team increased collecting aperture and gas volume in the detectors and added small collimators and telescopic devices to try and detect and then isolate spatially the discrete sources. Initial broadband nondispersive studies yielded confusing results at first that could not be reproduced, but Friedman believed they were detecting emissions from diffuse sources within the Milky Way. Meanwhile, in 1962, another x-ray group that grew out of cosmic-ray physics, led by Bruno Rossi and Riccardo Giacconi from American Science and Engineering and the Massachusetts Institute of Technology (MIT), succeeded in detecting the first nonsolar x-ray source, in the constellation of Scorpius, so dubbed Sco X-1.
In rapid response, Friedman flew an instrument with a better collimating system that pinned down the position of the source, and then went on to find other point sources, confirming as well the existence of a diffuse x-ray background. In 1963 they confirmed that the Crab Nebula in Taurus was a strong emitter of x-rays, and then in 1964, again using a naturally occurring celestial occultation, the passage of the lunar limb over the source on 7 July, they further localized the x-ray source and determined its structure and size. During the five-minute data-gathering window offered by the Moon and rocket flight trajectory, they thought the source would disappear quickly, but it dimmed gradually, which told them that the x-rays were coming from an extended source, the nebula itself in a volume at least one light year in extent, and not from the suspected central neutron star. And then in 1966, in a highly cited paper resulting from an Aerobee flight in 1965, Friedman’s group was the first to announce x-ray emission from an extragalactic source, the giant elliptical galaxy M[essier] 87.
NASA frequently consulted Friedman for long-range planning in x-ray astronomy. In the mid-1960s he suggested the possibility of using surplus Apollo-era hardware to create a huge crewed x-ray telescope in orbit as well as an “x-ray fence” on the Moon using the horizon as an occulting disk. His largest-scale endeavor was as a principal investigator in the High Energy Astrophysics Observatory (HEAO) mission series, which NASA began conceptualizing in the early 1960s. This was originally envisioned as a huge Titan launch platform carrying a wealth of instrumentation, equivalent to or greater than what could be carried aloft by high-altitude balloons and aircraft. Friedman was among those lobbying for this capability since the early 1960s. By 1970 the HEAO program was funded, and after various setbacks, its scope diminished by 1974. Friedman’s instrumentation survived severe cost-cutting measures and finally his bank of seven traylike thin-window collimated x-ray proportional counters, the NRL’s Large Area Sky Survey Experiment, flew on the first HEAO (A-1) launched in August 1977. In seventeen months of observations, in almost three full scans of the sky, it produced a sensitive map of the x-ray sky that added some 1,500 new sources beyond those already known from sounding rocket studies and from the Uhuru satellite, launched in 1970. HEAO A-1 data included spectrum, intensity, and time variations of sources in the 0.25 to 25 KeV energy range. These observations were accumulated into a vast databank on galactic and extragalactic sources that Friedman’s team, among others, mined for decades, resulting in scores of professional papers.
In the 1970s Friedman remained active in research and administration, but also began to write for the popular market. He had long been an active voice in scientific Washington, lending his expertise to policy issues through numerous venues including Richard Nixon’s PSAC, the Atomic Energy Commission, and the Space Science Board of the National Academy of Sciences. He received many honors and academic distinctions, and in 1968 won the National Medal of Science followed by the Wolf Foundation Prize in Physics in 1987 for cofounding x-ray astronomy. Herbert Friedman died of cancer at his home in Arlington, Virginia.
Oral and video histories with Herbert Friedman and his team members are housed at the American Institute of Physics Center for History of Physics, at the National Air and Space Museum (NASM), and at the Smithsonian Institution Archives. His papers are housed at the NRL and at the American Philosophical Society.
WORKS BY FRIEDMAN
“The X-ray K Absorption Edges of the Elements Iron to Germanium.” PhD diss., Johns Hopkins University, 1940.
With S. W. Lichtman and Edward Taylor Byram. “Photon Counter Measurements of Solar X-rays and Extreme Ultraviolet Light.” Physical Review 83 (1951): 1025–1030.
With Edward Taylor Byram, Talbot Chubb, and J. Kupperian. “Far Ultraviolet Radiation in the Night Sky.” In The Threshold of Space: The Proceedings of the Conference on Chemical Aeronomy, edited by M. Zelikoff. New York: Pergamon Press, 1957.
With Talbot Chubb and J. Kupperian. “A Lyman Alpha Experiment for the Vanguard Satellite.” In Scientific Uses of Earth Satellites, edited by James A. Van Allen. 2nd rev. ed. Ann Arbor: University of Michigan Press, 1958.
“X-ray and Ultraviolet Radiation Measurements from Rockets.” In Space Astrophysics, edited by William Liller. New York: McGraw-Hill, 1961.
With S. Bowyer, Edward Taylor Byram, and Talbot Chubb. “Lunar Occultation of X-ray Emission from the Crab Nebula.” Science, n.s., 146 (13 November 1964): 912–917.
———. “Cosmic X-ray Sources.” Science, n.s., 147 (22 January 1965): 394–398.
With Edward Taylor Byram and Talbot Chubb. “Cosmic X-ray Sources, Galactic and Extragalactic.” Science, n.s., 152 (1 April 1966): 66–71.
With Edward Taylor Byram. “X-rays from Sources 3C 273 and M 87.” Science, n.s., 158 (October 1967): 257–259.
With Edward Taylor Byram and Talbot Chubb. “Distribution and Variability of Cosmic X-ray Sources.” Science, n.s., 156 (April 1967): 374–378.
With A. Davidsen, S. Shulman, G. Fritz, et al. “Observations of the Soft X-ray Background.” Astrophysical Journal 177 (November 1972): 629–642.
The Amazing Universe. Washington, DC: National Geographic Society, 1975.
With R. Lucke, D. Yentis, G. Fritz, et al. “Discovery of X-ray Pulsations in SMC X-1.” Astrophysical Journal 206, pt. 2 (15 May 1976): L25–L28.
Reminiscences of 30 Years of Space Research. NRL Report 8113. Washington, DC: Department of Defense, Navy Research Laboratory, 1977.
With M. P. Ulmer, et al. “A Search for Extended Halos of Hot Gas in the Perseus, Virgo, and Coma Clusters.” Astrophysical Journal, 236, pt. 1 (15 February 1980): 58–62.
With Kent S. Wood. “The HEAO A-1 X-ray Source Catalog.” Astrophysical Journal Supplement 56 (December 1984): 507–649.
Sun and Earth. San Francisco: Scientific American Books, 1986.
The Astronomer’s Universe: Stars, Galaxies, and Cosmos. New York:W.W. Norton, 1990. Revised and updated, 1998.
DeVorkin, David. Science with a Vengeance: How the Military Created the US Space Sciences after World War II. New York: Springer-Verlag, 1992.
———. “Where Did X-ray Astronomy Come From?” Rittenhouse 10 (1996): 33–42.
Gursky, Herbert. “Herbert Friedman, 1916–2000.” Bulletin of the American Astronomical Society 32 (2000): 1665–1666.
Gursky, Herbert, and Frank Press. “Herbert Friedman.” Proceedings of the American Philosophical Society 146, no. 2 (2002): 195–203.
Hirsh, Richard F. Glimpsing an Invisible Universe: The Emergence of X-ray Astronomy. New York: Cambridge University Press, 1983.
Tucker, Wallace, and Riccardo Giacconi. The X-ray Universe. Cambridge, MA: Harvard University Press, 1985.