Decay properties of the very neutron-deficient isotopes ${}^{197–199}$Fr were studied at the velocity filter Separator for Heavy Ion reaction Products (SHIP) at GSI in Darmstadt. The isotopes were produced in the $2n–4n$ evaporation channels of the fusion-evaporation reaction ${}^{60}$Ni+${}^{141}$Pr $\to$ ${}^{201}$Fr*. Improved $\alpha$-decay properties of ${}^{199}$Fr were determined and the possible existence of two $\alpha$-decaying states in this nucleus is discussed. For the isotope ${}^{198}$Fr a broad $\alpha$-decay energy distribution was detected in the range of $(7470–7930)$ keV and two $\alpha$-decaying states were observed with half-lives of 1.1(7) and 15(3) ms. The new isotope ${}^{197}$Fr was identified based on the observation of one $\alpha$-decay chain yielding $E_{\alpha }=7728\left(15\right)$ keV and $T_{1/2}=0.6_{-0.3}^{+3.0}$ ms. The systematics of reduced $\alpha$-decay widths are presented for neutron-deficient francium, radon, and astatine isotopes.

• Received 29 January 2013

DOI:https://doi.org/10.1103/PhysRevC.87.044335