Named in honor of Robert M. Walker (1929– ), a leading figure in the study of radiation damage in solids and in the investigation of interstellar grains recovered from meteorites. His work on fission tracks with others opened a new approach to the dating of rocks on the earth and the moon and led to new information on the energy spectrum, composition and flux of solar and galactic cosmic rays. He founded whole new methods of scientific study and created a premier center for research in these new fields at Washington University, where he has provided inspiring leadership to a host of students and post-doctoral fellows. (M 34623) _ _.