Interaction of 28-GeV protons with tantalum: Charge dispersion and mass yields of light rare-earth nuclides

Abstract

Independent and cumulative yields of 24 light rare-earth nuclides between mass 143 and mass 157 produced in the interaction of 28-GeV protons with tantalum have been measured. Charge dispersion (CD) curves for masses 146, 148, and 149 have been constructed based on the results obtained from this work with the aid of some previously published data. The importance of feeding by $\ensuremath{\alpha}$ decay is discussed in detail. The difference between the position of the peak of the CD curve and that of $\ensuremath{\beta}$ stability ${Z}_{p}\ensuremath{-}{Z}_{A}$ appears to decrease from \ensuremath{\sim}3.4 at $A=146 \mathrm{to} \ensuremath{\sim}2.5$ at $A=149$. The total yields at these masses and at $A=123$ were evaluated from measured yields and CD curves. The trend of the mass yields over this range is a monotonic decrease with decreasing mass, consistent with a spallation mechanism. Comparison with Rudstam's spallation systematics shows fair agreement regarding the shapes of the CD and mass-yield curves, but with Rudstam's parameter choices the cross sections are overestimated and the ${Z}_{p}\ensuremath{-}{Z}_{A}$ values are not accurately reproduced. Comparison is made between the CD curves obtained in this work and those previously reported for $U$ interactions. The observations are consistent with the interpretation that the light rare-earth products from tantalum results from a spallation-like process, whereas there must be some fission contribution to the slightly neutron-deficient nuclides produced from uranium.NUCLEAR REACTIONS $^{181}\mathrm{Ta}(p, \mathrm{spallation})$, ${E}_{p}=28$ GeV; measured $\ensuremath{\sigma}(A;Z)$ for light rare-earth nuclides.