[en] Ion guide-based isotope separator has been used in order to study the superasymmetric fission mode at intermediate proton energies. These results, together with the fission fragment mass distributions obtained with HENDES array, indicate that fission at intermediate proton energies is a potential tool in producing nuclei near doubly magic ⁷⁸Ni. Furthermore the beta-decay of ⁶⁹Co has been identified for the first time and its half life has been measured. (author)

[en] The decays of ¹¹²Rh^g and ¹¹²Rh^m obtained as on-line mass separated fission products have been investigated by standard β and γ spectroscopic techniques and γ-γ angular correlations. Low-lying 0⁺ and 2⁺ states are identified in the daughter nucleus ¹¹²Pd. Systematics suggests the existence of an intruder band which is the lowest in ¹¹⁰Pd, i.e. two neutrons before the midshell. (orig.)

[en] Precise determination of the registration efficiency is an important part of each experiment. This task is especially difficult in case of neutrons. The only readily available calibration source is the continues neutron spectrum associated with spontaneous fission of Cf. This kind of a source is useful for verification of the efficiency data but for practical purposes one needs help from model calculations. For that purpose we have developed a new Monte- Carlo code BARBARA. The calculations are based on the neutron cross section libraries JENDL-3.2 and ENDF/B-VI. The main part of the code is devoted to the calculation of intrinsic efficiency for neutron detection. The simulation includes energy threshold for proton recoil energy (E_th). At least 10⁵ simulations were made for each efficiency point with a step of 100 keV from the threshold up to the energy of 5 MeV. The contribution of multiple neutron scattering was also simulated. Some of the results obtained for the NE102 detector are shown in figures. One of the conclusions of our simulations is that about 5.5% of the total of registered neutrons will suffer from diaphonic effect, shifting TOF deduced energies toward smaller values; typically about 40% of the original energy. At the same time, there will be a small shift (±1 cm) in apparent position. (authors)

[en] The nuclear structure studies performed since 1994 at the IGISOL online mass separator in Jyvaeskylae are reviewed and prospects for future studies are mentioned briefly

[en] The beta-decay of the neutron-rich nucleus ¹¹⁰Mo, separated by the IGISOL on-line mass separator from other fission products, has been investigated by using beta-gamma and gamma-gamma coincidence techniques. The decay scheme of ¹¹⁰Mo has been revised, including 3 new excited states and 7 new γ transitions in ¹¹⁰Tc. The β-feedings were measured and log ft values and B(GT) values were deduced based on a Q_β-value from systematics. Three excited 1⁺ states in ¹¹⁰Tc fed by spin-flip allowed-unhindered beta transitions were identified. The deduced beta-decay strengths are compared with the Gamow-Teller strength distribution obtained from a macroscopic-microscopic calculation. The role of the asymptotic quantum numbers in the context of the allowed beta-decay is discussed. (orig.)

[en] The primary fission fragment mass and kinetic energy distributions, and neutron multiplicities as function of fragment mass have been measured in the proton-induced fission of ²³⁸U at energies E_p=20, 35, 50 and 60 MeV using time-of-flight technique. Pre-scission and post-scission neutron multiplicities have been extracted from double differential distributions. The fragment mass dependence of the post-scission neutron multiplicities reveals the gross nuclear shell structure effect even at the higher proton energies we measured. The yields of neutron-rich fission products in the fission of ²³⁸U by 25 MeV protons were measured using an ion guide-based isotope separator technique. The results indicate enhancement for superasymmetric mass division at intermediate excitation energy of the fissioning nucleus. The experimental results have been analysed in the framework of a time-dependent statistical model with inclusion of nuclear friction effects in the fission process

[en] Presently, the Jyvaeskylae IGISOL facility delivers mass-separated beams of fission products with an intensity of 2700 ions/s per mb cross section. A further increase in yield is expected from the ongoing investigations into improving the design and understanding better the behavior of the fission ion guide. The study of new neutron-rich nuclei is hindered by the presence of different kinds of contaminants in the mass-separated beam: isobaric isotopes, isotopes of neighboring masses and doubly-charged ions. These problems will be solved by producing isotopically pure beams. We are developing an ion beam cooler+ion trap combination for this purpose

[en] For more than 10 years, neutron-rich nuclei produced in light-ion induced fission have been studied at the Ion Guide Isotope Separator On-Line (IGISOL) facility of the Department of Physics, University of Jyvaeskylae. The present performance of the system is briefly discussed. Some recent results concerning superasymmetric fission and β-delayed neutron emission are presented. The plans for producing isotopically pure beams are summarized

[en] The decays of the 9/2⁺ and of the three-quasiparticle high spin isomer in ⁹⁷Y have been investigated following on-line mass separation with the ion-guide technique. Spins and parities for several of the lowest-lying levels in the daughter nucleus ⁹⁷Zr are revised and configurations are proposed. In particular, the 2264 keV level is identified as the h_11/2 single-neutron level. The population of a cascade on top of the h_11/2 level provides evidence for Gamow-Teller β decay of the high-spin ⁹⁷Y isomer. Levels and transition rates are qualitatively well reproduced by regarding ⁹⁷Zr as a single-neutron nucleus with respect to the doubly closed ⁹⁶Zr core. copyright 1996 The American Physical Society

[en] The decay of ¹¹¹Ru obtained from fast on-line chemical and mass separation has been investigated by β-γ-t and γ-γ coincidence techniques. Earlier spin and parity assignments of ¹¹¹Rh levels based on extrapolations of level systematics are confirmed. In particular, the K=1/2 intruder band is supported by the hindrance of E2 transitions between deformed and spherical states and enhancement of intraband E2 transitions. The excitation energies of intruder band members in Rh isotopes show a minimum at ¹⁰⁹Rh₆₄, with two neutrons less than ¹¹¹Rh at the N=66 midshell. This trend, which differs from the one in the higher-Z neighbouring elements Ag and Cd with minima at N=66, follows the evolution of deformation observed in the lower-Z elements Ru and Mo. (orig.)