Decay properties of the very neutron-deficient isotopes [197][198][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 → 201 Fr*. Improved α-decay properties of 199 Fr were determined and the possible existence of two α-decaying states in this nucleus is discussed. For the isotope 198 Fr a broad α-decay energy distribution was detected in the range of (7470-7930) keV and two α-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 α-decay chain yielding E α = 7728(15) keV and T 1/2 = 0.6 +3.0 −0.3 ms. The systematics of reduced α-decay widths are presented for neutron-deficient francium, radon, and astatine isotopes.
Excited states in the highly neutron-deficient nucleus 162 W have been investigated via the 92 Mo( 78 Kr, 2α) 162 W reaction. Prompt γ rays were detected by the JUROGAM II high-purity germanium detector array and the recoiling fusion-evaporation products were separated by the recoil ion transport unit (RITU) gas-filled recoil separator and identified with the gamma recoil electron alpha tagging (GREAT) spectrometer at the focal plane of RITU. γ rays from 162 W were identified uniquely using mother-daughter and mother-daughter-granddaughter α-decay correlations. The observation of a rotational-like ground-state band is interpreted within the framework of total Routhian surface (TRS) calculations, which suggest an axially symmetric ground-state shape with a γ -soft minimum at β 2 ≈ 0.15. Quasiparticle alignment effects are discussed based on cranked shell model calculations. New measurements of the 162 W ground-state α-decay energy and half-life were also performed. The observed α-decay energy agrees with previous measurements. The half-life of 162 W was determined to be t 1/2 = 990(30) ms. This value deviates significantly from the currently adopted value of t 1/2 = 1360(70) ms. In addition, the α-decay energy and half-life of 166 Os were measured and found to agree with the adopted values.
Excited states in the odd-odd, highly neutron-deficient nucleus 166 Re have been investigated via the 92 Mo( 78 Kr, 3p1n) 166 Re reaction. Prompt γ rays were detected by the JUROGAM II γ -ray spectrometer, and the recoiling fusion-evaporation products were separated by the recoil ion transport unit (RITU) gas-filled recoil separator and implanted into the Gamma Recoil Electron Alpha Tagging spectrometer located at the RITU focal plane. The tagging and coincidence techniques were applied to identify the γ -ray transitions in 166 Re, revealing two collective, strongly coupled rotational structures, for the first time. The more strongly populated band structure is assigned to the πh 11/2 [514]9/2 − ⊗ νi 13/2 [660]1/2 + Nilsson configuration, while the weaker structure is assigned to be built on a two-quasiparticle state of mixed πh 11/2 [514]9/2 − ⊗ ν[h 9/2 f 7/2 ]3/2 − character. The configuration assignments are based on the electromagnetic characteristics and rotational properties, in comparison with predictions from total Routhian surface and particle-rotor model calculations.
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