Absolute yields of radionuclides produced in the spallation of cesium with 240-Mev protons have been measured from barium to ruthenium. The yields are based on the known cross section for the monitor reaction ${\mathrm{Al}}^{27}(p, 3pn){\mathrm{Na}}^{24}$. In agreement with the well-established pattern for high-energy spallation yields, the results indicate that the majority of reactions occur as primary knock-on collisions in which the incident proton interacts with only a few nucleons. This primary interaction is followed by a dissipation of the residual nuclear excitation, whose energy spread is very broad, leading to a distribution of products which reach far down the nuclide chart.

Measurement of absolute x-ray counting efficiencies for the $K$ x-rays of ${\mathrm{Xe}}^{131}$ and ${\mathrm{Mn}}^{55}$ in a methane beta-proportional counter and in a helium-alcohol G-M tube is also reported.

• Received 23 February 1954

DOI:https://doi.org/10.1103/PhysRev.94.1357