No abstract available

[en] We review structure data obtained by decay spectroscopy of neutron-rich nuclei of mass close to 100. Emphasis is put on the contribution of experiments at IGISOL in the nineties. They confirmed the earlier postulated shape coexistence in the fast shape-transition region between N = 58 (spherical ground states and low collectivity) and N = 60 (strong axial deformation). A detailed spectroscopic study of the A = 99 chain established the upper-Z limit of the N = 56 shell closure region with "9"9Nb, owing to striking similarities with "9"7Y. A consequence of the N = 56 closure is that the s_1_/_2 odd-neutron becomes the ground state of the most neutron-rich N = 57 isotones, starting with "9"9Mo, instead of the degenerated d_5_/_2 and g_7_/_2 subshells familiar in the tin region. Consequences on the change of spin on astrophysical r process calculations are briefly discussed. Finally, we say a few words about neutron rich rhodium and palladium isotopes near the neutron mid-shell where regular and intruder states coexist very close to each other. (authors)

[en] The retention behavior of volatile chlorides and oxychlorides of short-lived isotopes of group 5 elements Nb and 105 (Ha=hahnium) in quartz columns was studied using on-line isothermal gas chromatography. The 15-s ^99gNb was produced from a ²³⁵U-fission target at a reactor neutron beam line and 34-s ²⁶²Ha in fusion reactions of ¹⁸O+²⁴⁹Bk. Volatile chloride molecules were formed in a 900 C reaction oven by adding HCl as reactive gas. Depending on trace amounts of O₂ in the system, either the pentachlorides or the oxytrichlorides, or a mixture thereof, were formed. The isotopes ^99gNb and ²⁶²Ha were unambiguously identified after gas chromatographic separation by measuring the characteristic γ-lines of ^99gNb and by registering ²⁶²Ha-²⁵⁸Lr mother-daughter α-α correlations as well as spontaneous fission decays, respectively. The adsorption enthalpies of the investigated species on quartz surfaces were determined by analyzing the measured retention curves iwth a Monte Carlo model. Using an empirical correlation, the adsorption enthalpies were converted to sublimation enthalpies. The sublimation enthalpies of 95±16 kJ.mol^-1 and 124±16 kJ.mol^-1 determined for NbCl₅ and NbOCl₃, respectively, were in good agreement with literature data. In experiments with Ha-chlorides a yield curve with two components was observed. Sublimation enthalpies of ≤120 kJ.mol^-1 and 152±18 kJ.mol^-1 were estimated for HaCl₅ and HaOCl₃, rspectively. The estimated sublimation enthalpies were compared with theoretical predictions from relativistic calculations and with empirical extrapolations of chemical properties. In agreement with empirical extrapolations, a lower volatility was found for HaOCl₃ than for NbOCl₃. (orig.)

[en] The β-decays of ⁹⁹Y and ⁹⁹Zr have been investigated with the two recoil fission product separators JOSEF and LOHENGRIN. Half-lives of 1.51+-0.08 s and 2.1+-0.1 s respectively, have been determined. A β-decaying isomeric state has been observed in ⁹⁹Y. The level schemes of ⁹⁹₄₀Zr₅₉ and ⁹⁹₄₁Nb₅₈ have been established from γ-ray spectroscopy. Absolute γ-intensities have been obtained by means of two independent techniques. Half-lives of 293+-10 ns for the 251.9 keV state and 10.2+-1.5 ns for the 614.0 or 667.2 keV level in ⁹⁹Zr have been measured through delayed β,γ- and γ,γ-coincidence experiments. Values for the spins and parities of the low lying levels in ⁹⁹Zr are proposed in accordance with the systematics of lighter odd Zr isotopes. Spins and parities are assigned to some levels in ⁹⁹Nb from γ,γ-angular correlation measurements. In this nucleus there is evidence for three-particle configurations of some excited states, where the odd proton is coupled to two neutrons which are in different orbits. (orig.)

No abstract available

No abstract available

No abstract available

[en] The half-lives of the 469-keV level in ⁹⁹Nb and the 236-keV state in ⁹⁹Mo have been determined to (0.21 +- 0.06) ns and (0.87 +- 0.15) ns, respectively, from β, γ-delayed concidences. Values of B(E2) = (89 +- 28) e²fm⁴ and B(M1) = (0.017 +- 0.003)μsub(N)² are deduced for the 469-keV transition in ⁹⁹Nb and the 138-keV transition in ⁹⁹Mo. The result for the E2-transition probability seems to be in accordance with the particle-core coupling interpretation of the low-lying levels in ⁹⁹Nb if ⁹⁸Zr is used as the core. The M1 probability for ⁹⁹Mo agrees with the systematics for ''1-forbidden 1gsub(7/2) → 2dsub(5/2) neutron transitions. (orig.)

No abstract available

[en] Highlights: • Fourier transform (FT) spectra were used to extend the study of the hyperfine structure (HFS) of Nb I And Nb II energy levels. • HFS constants A for 68 levels of Nb I from 11,524.65 to 45,719.07 cm−1 were determined, of which 26 results are reported for the first time, as far as we know. Our study increased the total number of HFS constants A to 349 Nb I levels. • HFS constants A for 57 levels of Nb II from 2356.816 to 73,869.773 cm−1 were determined, of which 46 results are reported for the first time, as far as we know. Our study increased the total number of HFS constants A to 99 Nb II levels. Some of the archival data derived from the Fourier transform spectrometer (FTS) at the US National Solar Observatory ranging from 0 − 36,947 cm⁻¹ were investigated to study the hyperfine structure (HFS) patterns of Nb I and Nb II lines. The analysis of 155 lines in the FTS spectra was performed by a least squares fitting to derive values of the magnetic dipole HFS constant A. In total, the HFS constant A was determined for 68 levels of Nb I between 11,524.65 and 45,719.07 cm⁻¹ and for 57 levels of Nb II between 2356.816 and 73,869.773 cm⁻¹. 26 results for Nb I and 46 results for Nb II are reported for the first time, as far as we know.