Mass Spectrometric Studies of the Interaction of Gold with 3.0-Bev Protons

Gold targets have been irradiated with 3.0-Bev protons and the yields of cesium, barium, and rubidium nuclides investigated by mass spectrometry. A high-sensitivity surface-ionization technique, using a multiple filament source arrangement and capable of determining (within 5%) 10⁸ alkali metal atoms, was developed. The separation of products from the gold target was accomplished by extracting the gold into diethyl ether. The contamination level of stable Cs¹³³ in the gold foil and reagents was determined by isotope dilution methods to be {~}9×{}10⁹ atoms. Ratios of production cross sections for neutron-deficient cesium isotopes and their barium parents were calculated from mass spectra. Cross sections were placed on an absolute scale by a radiochemical determination of the Cs¹²⁷ cross section. No cesium isotopes with $A>128$ are formed in appreciable independent yield. An upper limit of 0.002 mb was placed on cross sections for Cs¹³² and the neutron-excess cesium isotopes. No stable cesium resulting from nuclear reactions was detected above the natural contamination background. Ratios of production cross sections for rubidium radioisotopes were determined. The natural contamination of rubidium was too large to place a meaningful limit on stable rubidium production.