Decay of mass-separated 199Pom and 199Pog.

Abstract

Sources of $^{199}\mathrm{Po}^{\mathrm{m}}$ and $^{199}\mathrm{Po}^{\mathrm{g}}$ have been produced and mass separated on line. Multiscaled spectra of \ensuremath{\gamma} rays, x rays, and conversion electrons, and \ensuremath{\gamma}-\ensuremath{\gamma} and \ensuremath{\gamma}-x-ray coincidences were measured. The M4 isomeric transition of the ${(13/2)}^{+}$ state of $^{199}\mathrm{Po}$, with a half-life of 4.17 min, was observed for the first time, permitting the placement of the ${(13/2)}^{+}$ and ${(5/2)}^{\mathrm{\ensuremath{-}}}$ levels above the ${(3/2)}^{\mathrm{\ensuremath{-}}}$ ground state. Also, the placement of the ${(13/2)}^{+}$ state in Po together with previously reported \ensuremath{\alpha}-decay Q values made possible the location of the ${(13/2)}^{+}$ isomeric state in $^{195}\mathrm{Pb}$. From an analysis of \ensuremath{\gamma}-\ensuremath{\gamma}-t coincidence data and energy sums, 26 transitions were placed in a decay scheme between 23 levels in $^{199}\mathrm{Bi}$. On the basis of systematics the population of a ${(1/2)}^{+}$ isomeric state in $^{199}\mathrm{Bi}$ was deduced. The isomeric (M4) transition to the ${(9/2)}^{\mathrm{\ensuremath{-}}}$ ground state was not observable in the present data; its rate is at least 390 times less than the Weisskopf single particle estimate.