Robert M. Walker, PhD, Professor of Physics in Arts & Sciences and a faculty fellow of the McDonnell Center for the Space Sciences, died of stomach cancer Thursday, 12 February 2004, in Brussels, Belgium. He was 75. Walker worked on the frontiers of space research for more than four decades.
Robert Walker was born in Philadelphia on 6 February 1929. His mother was Dorothy Potter and he considered Roger Potter his father though he was not his biological father. His early years were spent in New York City and in upstate New York. He attended the Bronx High School of Science, earned his BS in physics from Union College and in 1954, he received his PhD in particle physics from Yale University. He subsequently joined the General Electric Laboratory in Schenectady, New York where he studied the radiation effects in solids. His work on defects in irradiated copper is still regarded as the definitive work on the topic. In the early 1960s, Walker's discovery of fossil nuclear particle tracks in minerals was instrumental to new developments in geo-chronology and cosmic ray physics. In particular, his discovery of tracks from nuclei heavier than iron opened a new frontier of cosmic ray physics. He subsequently pioneered the use of plastics to detect and count such nuclei in cosmic ray balloon flights.
Beginning in 1966, when he moved to Washington University and became the first McDonnell Professor of Physics, his research interests turned more toward space physics. He was the inaugural director of the McDonnell Center, which was established in 1975 by a gift from aerospace pioneer James S. McDonnell.
Walker was a member of the NASA committee that allocated samples of the first returned lunar materials, and his laboratory led the way in deciphering their record of lunar, solar system and galactic evolution. Together with Ghislaine Crozaz and other colleagues, Walker made path breaking laboratory studies of the first moon rocks revealing the history of solar radiation and cosmic rays within these samples. He and Dr. Crozaz were married in 1973. In the past two decades, he was a world leader of microanalytical studies of tiny grains preserved for eons in meteorites, culminating in their identification as stardust. More recent achievements include the design of micrometeorite capture cells that were flown aboard NASA's Long Duration Exposure Facility; verification of the extraterrestrial origin of dust particles collected in the upper atmosphere; and the successful search for interstellar grains in meteorites.
"Bob was such a dominant force for excellence in our department and the University over so many years, it is hard to grasp that he is gone," said John W. Clark, PhD, chair of physics, the Wayman Crow Professor and a faculty fellow of the McDonnell Center. "His passion for life and science was an inspiration to us all, and his legacy will endure in the work of his many colleagues and the extended family of his former students."
Walker led the McDonnell Center, which includes one of the world's largest research groups dedicated to the search for and investigation of extraterrestrial materials, until 1999. "Washington University would be a lesser institution without the contributions of Bob Walker," said William H. Danforth, chancellor emeritus and vice chairman of the Board of Trustees. "He gave us inspiration, enthusiasm, great science and visionary leadership. He built the strength of the McDonnell Center for the Space Sciences. He convinced others of the potential for the modern Department of Earth and Planetary Sciences. He had always the respect and affection of us all."
The last two decades of Walker's career were driven by his remarkable vision and his excitement at the prospect of profound discovery. His recognition of the potential importance of the ion microprobe for making isotopic measurements on microscopic samples, and his acquisition in 1982 of a state-of-the-art instrument for the University, led directly to a series of spectacular results. Chief among these was the identification and characterization of stellar condensates in meteorites, which opened a window into stellar evolution and the creation of the heavier elements.
Always in pursuit of more powerful ways to analyze small amounts of material, Walker devoted the last years of his life to the implementation of nanoscale secondary-ion mass spectrometry (NanoSIMS) promoting the development, acquisition and application of the most advanced instrument of its kind. This effort was rewarded with the discovery, which he had forecast years earlier, of presolar silicate grains in interplanetary dust particles.
The Robert M. Walker Symposium at the University in March 2003 honored his contributions and achievements. He was elected to the National Academy of Sciences in 1973. Among his other honors are the E.O. Lawrence Memorial Award of the U.S. Atomic Energy Commission, the J. Lawrence Smith medal of the National Academy of Sciences, the Leonard medal of the Meteoritical Society and the Antarctic Service Medal. He received honorary doctorates from Union College (1967), the French University of Clermont-Ferrand (1975) and Washington University (2004). He was also one of the founders, and first president, of VITA (Volunteers in Technical Assistance), an organization that provides technological expertise to third world countries.
Walker and his wife maintained a residence in St. Louis County but in 2001, Bob became a part time visiting professor at the University of Brussels. It was in Brussels that his fatal illness was correctly diagnosed. In addition to his wife, Walker is survived by his sons, Eric and Mark Walker; and three grandchildren. His most important legacy will remain the sizable number of students, postdocs, and colleagues within the meteoritic and cosmochemist communities that he mentored and inspired.
Portions of this obituary are based upon one given in the on-line Record of Washington University and another published by Floss, Sandford and Zinner in Meteoritics and Planetary Science (39:1409-1411, 2004).