Alpha-Emitting Isomeric State ofTb149

Abstract

Bombardment of ${\mathrm{La}}^{139}$ targets with 80- to 140-Mev ${\mathrm{O}}^{16}$ ions has resulted in the identification of a new alpha activity decaying with a half-life of 4.3±0.2 min and an alpha-particle energy of 3.99±0.03 Mev. Subsequent experiments have established that the activity is due to an isomeric state of ${\mathrm{Tb}}^{149}$. It is proposed that the isomerism due to the filling of an $h_{\frac{11}{2}}$ proton state for the spherical Tb isotopes.