Interaction of 28-GeV protons with thorium: Study of charge dispersions and mass yields

Abstract

Yields of 53 nuclides ranging from $^{43}\mathrm{Sc}$ to $^{173}\mathrm{Hf}$ (with the majority in the rare-earth region) produced in the interaction of 28-GeV protons with thorium have been measured. Cumulative yields for neutron-rich nuclides with $A\ensuremath{\ge}140$ exhibit similar mass dependence as those in low-energy fission. Charge dispersion curves for $A=146$ and $A=170$ have been constructed based on independent and cumulative yields measured in this work for these masses and the published data on cesium isotopes. Total isobaric yields for 18 mass numbers were evaluated from results obtained in this study and earlier investigations. The overall shape of the mass-yield curve is thus determined. The hump of the mass-yield curve in the middle $50\ensuremath{\le}A\ensuremath{\le}150$ can be attributed mainly to binary fission but the broad background underneath probably cannot be accounted for by spallation alone. The charge dispersion curves and the mass-yield curve for thorium are qualitatively similar to those for uranium. However, the neutron-rich cumulative yields are 3-5 times smaller in thorium than in uranium targets; the fission peak from thorium is shifted to lower mass and the yields are shifted slightly toward higher neutron deficiency when compared with the yields from uranium.NUCLEAR REACTIONS, FISSION $^{232}\mathrm{Th}(p,f)$, ${E}_{p}=28$ GeV; measured $\ensuremath{\sigma}(A,Z)$, 53 products $^{43}\mathrm{Sc}$-$^{173}\mathrm{Hf}$; deduced charge dispersion curves and mass-yield curve. mass, chemically separated samples.