[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] Cross-sections for nuclide production in fast-neutron induced fission of natural uranium are part of the input for predictions of yields of neutron-rich nuclides obtainable at Radioactive Ion Beam facilities. We first describe the neutron spectra produced according to the scheme once envisaged for SPES (protons on an enriched "1"3C target) and the one adopted for SPIRAL2 (deuterons on natural carbon), which both have been measured at JYFL. We then present the measurements of Z-splits in isobaric chains performed at IGISOL. When coupled with the fission cross-section and A-splits for the relevant neutron spectrum, they allow estimates of nuclide cross-sections. It looks that calculations, even those based on modern libraries, are too optimistic by about a factor of two. (authors)

[en] The study of β-delayed neutron emission plays a major role in different fields such as nuclear technology, nuclear astrophysics and nuclear structure. However the quality of the existing experimental data nowadays is not sufficient for the various technical and scientific applications and new high precision measurements are necessary to improve the data bases. One key aspect to the success of these high precision measurements is the use of a very pure ion beam that ensures that only the ion of interest is produced. The combination of the IGISOL mass separator with the JYFLTRAP Penning trap is an excellent tool for this type of measurement because of the ability to deliver isobarically and even isomerically clean beams. Another key feature of the installation is the non-chemical selectivity of the IGISOL ion source which allows measurements in the important region of refractory elements. This paper summarises the β-delayed neutron emission studies that have been carried out at the IGISOL facility with two different neutron detectors based on "3He counters in a polyethylene moderator: the Mainz neutron detector and the Beta delayed Neutron detector. (authors)

[en] The Moessbauer effect of ⁵⁷Fe implanted into diamond structure semiconductors, Ge, Si and C, has been studied by in-beam implantation of ⁵⁷Fe ions, which were excited to the 14 keV state by a ³⁵Cl beam from a tandem Van de Graaff accelerator. The time between the stopping of the ⁵⁷Fe nucleus and the emission of the 14 keV γ-ray is determined by the lifetime (140 ns) of the 14 keV state. In each material the Moessbauer spectrum exhibits a doublet with velocity coordinates (in mm/s) at room temperature, relative to a sodium ferrocyanide absorber, as follows: diamond (-0.99, 1.10), silicon (-0.80, 0.21), and germanium (-0.88, -0.02). In silicon and germanium crystals the spectra were observed over the temperature range between 13 K and 870 K. The relative line intensities changed dramatically and the positions of the lines shifted systematically with temperature. In addition, channelling studies were made on iron that had been implanted into silicon. (orig.)

[en] In order to determine whether the doublet observed in the Moessbauer spectra of ⁵⁷Fe after in-beam, recoil implantation into Ge is due to a quadrupole interaction or corresponds to two implantation sites, this implantation experiment was performed in the presence of a 35 kG external magnetic field. The resulting Moessbauer spectrum favors a dominant quadrupole interaction hypothesis. (orig.)

[en] A tabulation of NMR/ON experiments is given. Results published or communicated up to August 1980 were considered. (orig.)

[en] ¹⁹⁷Hg, ¹⁹⁹Tl and ¹⁹⁹Au ions were implanted into Zn single crystals. From time differential perturbed e^--γ and β-γ angular correlation experiments with the 5/2^- states in ¹⁹⁷Hg and ¹⁹⁹Hg, respectively, the quadrupole interaction for Hg in Zn is reinvestigated. Only the data for the ¹⁹⁹Au sample exhibit a single unique quadrupole precession pattern in agreement with the result of the lattice location studies by use of the channeling technique, which show Hg to occupy random lattice sites in Zn while Au is substitutional. From the measured interaction frequency, sign and magnitude of the effective electric field gradient for Hg on the substitutional site in Zn is determined as Vsup(eff)sub(zz) = +15.2(1.8) x 10¹⁷V x cm^-2. By comparison of this value to the corresponding lattice field gradient contribution an electronic enhancement factor of K(HgZn) = 2.6 is deduced in disagreement with a previous derivation of this quantity, but which supports the proposal that the electronic field gradient depends linearly upon the valence of the impurity probe atom. (orig.)

[en] The quadrupole frequencies, e²qQ/h, for sup(186,188-190)Ir in a Re single crystal have been determined by nuclear orientation at temperatures down to 2 mK. Using a model-dependent value of + 1.0 b for the quadrupole moment of the ground state of ¹⁸⁹Ir, the electric field gradient of IrRe at 0 K is found to be -3.6 x 10¹⁷ V x cm^-2. The value is consistent with systematics proposed by Raghavan et al. Using this EFG, quadrupole moments are deduced for sup(186,188,190)Ir. (orig.)

[en] The radiation damage effects on the electric quadrupole interaction (QI) for the system SnCd were investigated with the time-differential perturbed angular distribution (TDPAD) method and three nuclear reaction recoil Sn probes, in the temperature range from 80 to 590 K. The obtained results are consistent with a static defect QI strength distribution (delta approx. equal to 10%) around a mean value comparable with the unique QI strength corresponding to the undistorted crystal lattice. (orig.)

[en] The half-life of ⁶⁴Cu in Cu-Au solid solutions has been measured as a function of the Cu concentration. Relative changes of electron densities Δrho(0)/rho(0) at the Cu nucleus are deduced. The observed nonlinear concentration dependence of Δrho(0)/rho(0) is discussed in terms of volume and charge transfer effects. (Auth.)