Alpha-Particle Bombardment ofA36andA40

Abstract

Gas targets (130-kev thick) of natural argon (99.6% ${\mathrm{A}}^{40}$; 0.34% ${\mathrm{A}}^{36}$) and of argon enriched in ${\mathrm{A}}^{36}$ (97.4% ${\mathrm{A}}^{36}$; 2.5% ${\mathrm{A}}^{40}$) have been bombarded with 7.4-Mev alpha particles from the Yale cyclotron. Protons and neutrons at 90° to the incident beam have been studied by means of 50μ Ilford $C-2\mathrm{}$ emulsions, placed 16 cm from the target. The ground-state $Q$-value for the ${\mathrm{A}}^{36}(\alpha , p){\mathrm{K}}^{39}$ reaction is -1.28 Mev, with excited states at 2.50 and 2.87 Mev. The ground state $Q$ for ${\mathrm{A}}^{40}(\alpha , p){\mathrm{K}}^{43}$ is -3.36 Mev, with excited states at 0.65 and 1.18 Mev. The cross sections for these two reactions, as well as for the ${\mathrm{A}}^{40}(\alpha , n){\mathrm{Ca}}^{43}$ reaction, have been measured and are found to be in general agreement with the predictions of simple compound-nucleus theory.