Half-lives ofRn199andRnm199

Abstract

The nuclide $^{199}\mathrm{Rn}$ and the isomer $^{199}\mathrm{Rn}^{m}$ were produced in the reaction $^{169}\mathrm{Tm}(^{35}\mathrm{Cl},5n)^{199}\mathrm{Rn}$. An electromagnetic velocity filter separated the recoiling residual nuclei from the beam at zero degree. The nuclei were embedded into a surface-barrier detector recording both the arrival pulse and the alpha-decay event. The half-life for $^{199}\mathrm{Rn}$ in its presumed ground state (${E}_{a}=6.99$ MeV) has been determined as 0.5 \ifmmode\pm\else\textpm\fi{} 0.2 sec and the half-life of $^{199}\mathrm{Rm}^{m}$ (${E}_{a}=7.06$ MeV) is 0.29 \ifmmode\pm\else\textpm\fi{} 0.05 sec.[RADIOACTIVITY $^{199}\mathrm{Rn}$ and $^{199}\mathrm{Rn}^{m}$; measured half-lives.]