αdecay of the very neutron-deficient isotopes197–199Fr

Decay properties of the very neutron-deficient isotopes ${}^{197\char21{}199}$Fr were studied at the velocity filter Separator for Heavy Ion reaction Products (SHIP) at GSI in Darmstadt. The isotopes were produced in the $2n\char21{}4n$ evaporation channels of the fusion-evaporation reaction ${}^{60}$Ni+${}^{141}$Pr $\ensuremath{\rightarrow}$ ${}^{201}$Fr*. Improved $\ensuremath{\alpha}$-decay properties of ${}^{199}$Fr were determined and the possible existence of two $\ensuremath{\alpha}$-decaying states in this nucleus is discussed. For the isotope ${}^{198}$Fr a broad $\ensuremath{\alpha}$-decay energy distribution was detected in the range of $(7470\char21{}7930)$ keV and two $\ensuremath{\alpha}$-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 $\ensuremath{\alpha}$-decay chain yielding ${E}_{\ensuremath{\alpha}}=7728(15)$ keV and ${T}_{1/2}=0.{6}_{\ensuremath{-}0.3}^{+3.0}$ ms. The systematics of reduced $\ensuremath{\alpha}$-decay widths are presented for neutron-deficient francium, radon, and astatine isotopes.