Interactions of Cadmium-106 with Alpha Particles

Abstract

The excitation functions of the ($\alpha , \gamma$), ($\alpha , n$), ($\alpha , p$), ($\alpha , 2n$), ($\alpha , \mathrm{pn}$), $(\alpha , 3n)+(\alpha , p2n)$, ($\alpha , \alpha n$), and ($\alpha , 2\alpha n$) reactions of reactions of ${\mathrm{Cd}}^{106}$ have been determined with alpha particles of 6-39-MeV kinetic energy. Reactions involving charged-particle emission compete quite favorably with those involving neutron emission only; the large Coulomb barrier for charged-particle emission is partially offset by the relatively low separation energies for these charged particles, as compared to those for neutrons. Thus, some of the peak cross sections (and corresponding alpha-particle energies) are: ($\alpha , n$), 626 mb (19 MeV); ($\alpha , p$), 243 mb (22 MeV); ($\alpha , 2n$), 427 mb (32 MeV); ($\alpha , \mathrm{pn}$), 230 mb (35 MeV); and ($\alpha , \alpha n$), 205 mb (37 MeV). Comparison of these data with the previously determined excitation functions for ${\mathrm{Sn}}^{124}$ clearly demonstrates that the reactions leading to charged-particle emission in neutron-deficient ${\mathrm{Cd}}^{106}$ are much probable than are the analogous reactions on neutron-excess ${\mathrm{Sn}}^{124}$. The ratio of the sum of cross sections involving the emission of at least one charged particle to the sum of cross sections for the emission only of neutrons is more than an order of magnitude greater for ${\mathrm{Cd}}^{106}$ than for ${\mathrm{Sn}}^{124}$. This behavior may be reproduced with the statistical theory of nuclear reactions, by using $r_o=1.7\mathrm{}$ F for the radius parameter and $a=1.8/\mathrm{MeV}$ for the level-density parameter. Detailed comparison of the data with compound nucleus theory shows good agreement for the ($\alpha , n$), ($\alpha , p$), and ($\alpha , \alpha n$) excitation functions. A brief discussion of the principles of $4\pi$ scintillation counting is also presented.