Radioactive Decay of the Isomers of Americium-242

The decay characteristics of the two isomers of ${\mathrm{Am}}^{242}$ have been investigated. The beta decay of the 16-hour ${\mathrm{Am}}^{242m}$ has a branching ratio of 51±5% to the first-excited state (42.3 kev) of ${\mathrm{Cm}}^{242}$ with the remainder of the decay going to the ground state. The electron capture decay of ${\mathrm{Am}}^{242m}$ has a branching ratio of approximately 60% to first-excited state (44.8 kev) of ${\mathrm{Pu}}^{242}$. An upper limit of 6% has been set for the fraction of ${\mathrm{Am}}^{242m}$ decay via isomeric transition. The beta decay of the 100-year ${\mathrm{Am}}^{242}$ has a branching ratio of 45±5% to the first-excited state of ${\mathrm{Cm}}^{242}$ with the remainder of the decay going to the ground state. The beta-spectrum end points for ${\mathrm{Am}}^{242m}$ and ${\mathrm{Am}}^{242}$ have been measured to be 620±10 kev and 585±10 kev, respectively. A decay scheme for the two isomers has been proposed. $\mathrm{Log}\mathrm{ft}$ values have been calculated for beta and electron capture decay of the isomers and are discussed in conjunction with spin and parity assignments.