Radiotracer Measurement of the Desorption Energy of Silver from Molybdenum and Nickel

When Cd107 undergoes decay by electron capture, the radioactive daughter Ag107m is given sufficient energy by neutrino recoil to enable it to escape from adsorbed sites. Sources of Cd107 were made of sufficient strength and cleanliness to enable use of the recoiling Ag107m as a very pure beam of tracer atoms to study surface interactions of silver with thermally cleaned polycrystalline foils of molybdenum and nickel. Constant beams of Ag107m with intensities greater than 106 particles per minute were attained in 1% geometry. The desorption energy of silver on molybdenum was found to be 1.9±0.3 eV, and of silver on nickel, 1.6±0.3 eV. All measurements were made under ultra-high-vacuum conditions, and techniques were developed to permit using a volatile isotope in a baked-out system.