Photoprotons fromMo100andMo92

Abstract

The absolute yield and the energy and angular distributions of protons emitted from targets of concentrated isotopes ${\mathrm{Mo}}^{92}$ and ${\mathrm{Mo}}^{100}$, under betatron x-ray radiation of maximum energy 22.5 Mev, have been determined with nuclear emulsions as detector of protons.For ${\mathrm{Mo}}^{92}$ the proton is less tightly bound than the neutron by 5.0 Mev; for ${\mathrm{Mo}}^{100}$ the proton is more tightly bound by 2.4 Mev. Comparison of the large yield and the energy distribution of protons from ${\mathrm{Mo}}^{92}$ with those calculated from the statistical model shows good agreement except for an observed excess of high energy protons, which are also anisotropic. They are presumably due to a direct emission process with which neutron emission does not compete in the normal way.With ${\mathrm{Mo}}^{100}$, however, the yield, though 20 times smaller, exceeds the yield predicted on the statistical model by 20 to 125 times depending upon the processes and parameters assumed in the calculation. Most of the protons, therefore, must come from a direct process. The observed energy distribution is similar to one computed using the experimental ($\ensuremath{\gamma}, p$) cross section if it is assumed that the residual nucleus is left with a typical exponential energy level density distribution. The angular distribution is strongly anisotropic with a maximum near 45\ifmmode^\circ\else\textdegree\fi{}, for protons of energy greater than 5 Mev.