Ultra-high vacuum techniques

Abstract

Cross sections for the formation of a number of lanthanides by the interaction of 28-GeV protons with uranium, bismuth, and gold were measured by a radiochemical method. Yield-vs.-mass curves and some information concerning the charge dispersion curves were deduced from the independent and cumulative cross sections. The yield-vs.-mass curve for uranium shows a rapid decrease with increasing mass in the region from A = 131 to A ≈ 150. The total isobaric yields appear to reach a valley or flat region at A ≈ 155. Examination of neutron deficient (NZ ⩽ 1·38) and neutron excess products (NZ > 1·38) indicates the observed decrease in the total yields is due primarily to a rapid decrease in yields of the neutron excess products. The charge dispersion curve for products from uranium in the rare earth region is double peaked. The valley separating the neutron excess and neutron deficient peaks is deeper in the europium region than that reported previously in the cesium region. Total isobaric yields in the mass 134–155 region from bismuth and gold targets are approximately constant at ≈11 mb, a higher value than those reported for products in the mass 72–131 region from lead targets. The charge dispersion curves for rare earth products from Bi and Au show single peaks on the neutron deficient side of stability. The results are discussed in terms of fission and spallation as possible mechanism leading to products in the rare earth region.