Oral histories in meteoritics and planetary science: IV. James R. Arnold

James Arnold, a nuclear chemist, reports in this interview, taped during th e Meteoritical Society meeting in Chicago in 2000, that he became intereste d in meteorites when one of his graduate students chose to search for the c osmogenic isotope, Mn-53, in an iron meteorite. This project led to analyse s of what became the standard four cosmogenic isotopes (Mn-53, Cl-36, Al-26 , and Be-10) in meteorites and to the first determinations of their terrest rial ages. These in turn paved the way for analyses of a broad set of short - and long-lived isotopes in lunar samples returned by the Apollo astronaut s, providing insight into lunar surface processes and the history of cosmic radiation. Arnold also mounted gamma-ray spectrometers on the command modu les of the Apollo 15 and 16 missions and obtained chemical maps of the surf ace materials in mare and highlands regions. In 1958 Arnold began his resea rch and teaching at the University of California at San Diego where from 19 83 to his retirement in 1993 he served as the Harold C. Urey Professor of C hemistry. In 1976, the Meteoritical Society honored James Arnold with its L eonard Medal.