Isomeric States of Po Isotopes in the Nanosecond Range Populated byPb(α, xn)Reactions

Abstract

Isomeric states of Po isotopes from $A=204$ to $A=211$ have been investigated by means of the nanosecond time analysis of $\mathrm{Pb}(\ensuremath{\alpha}, xn)$ $\ensuremath{\gamma}$ rays produced in natural beam bunches of a cyclotron. In addition to those already reported, new isomeric states have been revealed systematically. The following half-lives have been measured: $^{204}\mathrm{Po}$: 190\ifmmode\pm\else\textpm\fi{}20 nsec; $^{206}\mathrm{Po}$: 160\ifmmode\pm\else\textpm\fi{}40 nsec; $^{208}\mathrm{Po}$: 380\ifmmode\pm\else\textpm\fi{}100 nsec; and $^{210}\mathrm{Po}$: 110\ifmmode\pm\else\textpm\fi{}10 nsec. The possibility that such half-lives are associated with the expected 8+ state of predominant configuration ${{h}_{\frac{9}{2}}}^{2}(p)$ is discussed. Another half-life (24 nsec) found in $^{210}\mathrm{Po}$ was assigned as a (${h}_{\frac{9}{2}}{i}_{\frac{13}{2}}$) 11 - isomeric state. Odd isotopes show three-particle isomeric states in addition to the ${i}_{\frac{13}{2}}(n)$ isomeric state. Several characteristic features revealed in this study are discussed.