Observation ofTm149decay toEr149levels andβ-delayed proton emission

With the use of an on-line isotope separator, ${}_{}{}^{149}{}_{}{}^{}\mathrm{Tm}$ ($T_{1/2}$=0.9±0.2 s) was identified in ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ bombardments of ${}_{}{}^{94}{}_{}{}^{}\mathrm{Mo}$. Seven γ rays were observed to follow the isotope’s (${\beta }^{+}$+electron capture) decay, including the 111.3-keV transition known from ${}_{}{}^{149}{}_{}{}^{}\mathrm{Er}_{}^{\mathrm{m}}{}_{}{}^{}$ isomeric decay to be the $d_{3/2}$ (111.3 keV)→$s_{1/2}$ (0.0 keV) γ ray in ${}_{}{}^{149}{}_{}{}^{}\mathrm{Er}$. In addition to the previously known levels at 111.3 ($d_{3/2}$) and 741.5 ($h_{11/2}$) keV in ${}_{}{}^{149}{}_{}{}^{}\mathrm{Er}$, our data establish three other excited states, at 907.4 ${\left(\right(5/2\mathrm{}}^{+}$), 1066.2 ${\left(\right(7/2\mathrm{}}^{\mathrm{-}}$), and 1482.9 ${\left(\right(9/2\mathrm{}}^{\mathrm{-}}$, ${(11/2\mathrm{}}^{\mathrm{-}}$) keV. Coincidences observed between Er K x rays and protons in the A=149 mass chain show that ${}_{}{}^{149}{}_{}{}^{}\mathrm{Tm}$ is a β-delayed proton precursor.