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Cross sections for formation of cesium and rubidium isotopes produced by bombardment of uranium with protons ranging in energy from 0.1 to 6.2 GeV were measured both radiochemical^ and mass spectrometrically. Independent yields were determined for Rb 84 , Rb 86 , Cs m , Cs m , Cs 130 , Cs 131 , Cs 132 , Cs 134 , Cs 136 , and, at some energies, Rb 83 and Cs 136 . In addition, the independent yield of Ba 131 and the chain yields of Cs 126 , Cs 127 , Cs 129 , La 131 , Cs 135 , Cs 137 , Rb 83 , Rb 87 , and Ba 140 were obtained. The formation cross sections of the Cs and Ba products on the neutron-excess side of stability decrease monotonically with increasing energy above 0.1 GeV, whereas the excitation functions for independent formation of the more neutron-deficient products in the Cs-Ba region and of Rb 84 and Rb 86 all go through maxima. The proton energies at which these maxima occur fall on a smooth curve when plotted against the neutron-proton ratio of the product, with the peaks moving to higher energies with decreasing neutron-proton ratio. Under the assumption that the mass-yield curve in the region 125

X-ray fluorescence (XRF) analysis has played an important role in elemental chemical analysis for many years. The synchrotron radiation (SR) X-ray source that has been developed in the last 10-20 years represents a revolutionary improvement in X-ray production technology. By using SR for XRF analysis, researchers can make measurements with improved sensitivity and spatial resolution.Results obtained with SR show that measurements with a spatial resolution of less than 100 ftm2 and a minimum detection limit (MDL) approaching 1 fg can be made in just 300 s. The XRF method traditionally has been used because of its multielement detection capability, minimal sample preparation, minimal damage to the sample, and ability to operate at atmospheric pressure with solid, liquid, or gaseous samples. The substitution of the SR source preserves all these attributes and opens new opportunities for exploiting the XRF method. For example, a trace element X-ray microscope can be used to

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