Proton Decay of an Intruder State in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>B</mml:mi></mml:mrow><mml:mprescripts/><mml:mrow/><mml:mrow><mml:mn>185</mml:mn></mml:mrow><mml:mrow/><mml:mrow/></mml:mmultiscripts></mml:mrow><mml:mi>i</mml:mi></mml:math>

The new proton radioactivity ${}^{185m}\mathrm{Bi}$ has been observed, produced via the ${}^{95}\mathrm{Mo}{(}^{92}\mathrm{Mo},pn{)}^{185}\mathrm{Bi}$ reaction. Its decay proceeds from the low-lying ${\frac{1}{2}}^{+}$ intruder state in ${}^{185}\mathrm{Bi}$ to the ${}^{184}\mathrm{Pb}$ ground state with the emission of a proton of energy $1.585\ifmmode\pm\else\textpm\fi{}0.009\mathrm{MeV}$ and a half-life of $44\ifmmode\pm\else\textpm\fi{}16\ensuremath{\mu}\mathrm{s}$. This marks the first observation of proton radioactivity above the $Z\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}82$ closed shell, and it has been used to obtain the admixture of a ${0}^{+}$ intruder state in ${}^{184}\mathrm{Pb}$ into the ${}^{184}\mathrm{Pb}$ ground-state wave function.