Alpha-particle and $\gamma$-ray spectral measurements were made for ${}_{}{}^{205-208}{}_{}{}^{}\mathrm{Fr}$. A new $\alpha$ emitter ($T_{\frac{1}{2}}=0.7\mathrm{}\pm 0.1$ sec and $E_{\alpha }=6.930\mathrm{}\pm 0.005$ MeV) was observed and identified with the decay of a previously unknown isomer in ${}_{}{}^{206}{}_{}{}^{}\mathrm{Fr}$. From the $\alpha$ particle and $\gamma$ ray intensities, $\alpha$ decay branching ratios were deduced for ${}_{}{}^{205-208}{}_{}{}^{}\mathrm{Fr}$ utilizing available information concerning the nuclides' (electron capture + positron) decay properties. Reduced widths were calculated and compared with those of neighboring nuclei.

RADIOACTIVITY ${}_{}{}^{205,206,207,208}{}_{}{}^{}\mathrm{Fr}$, measured $E_{\gamma }$, $I_{\gamma }$, $E_{\alpha }$, $I_{\alpha }$; deduced $\alpha$-branching ratios; identified ${}_{}{}^{206}{}_{}{}^{}\mathrm{Fr}_{}^m{}_{}{}^{}$. Mass separation.

• Received 12 January 1981

DOI:https://doi.org/10.1103/PhysRevC.23.2342