[en] The decays of seniority isomers in the N=82 nuclei ¹⁵⁰Er and ¹⁵²Yb and in their respective N=81 isotopes ¹⁴⁹Er and ¹⁵¹Yb were studied following mass separation by the Argonne Fragment Mass Analyzer. Conversion electrons were detected with Si p-i-n diodes operated at room temperature. The low-energy isomeric transitions in ^151,152Yb have been observed for the first time in the electron spectra. Multipolarity assignments were made for many of the decay γ rays of the four nuclei

[en] With the use of mass separators, on-line at heavy-ion accelerators, they have investigated the particle-decay properties of nuclei at and near closed shells. They find that the proximity of magic configurations leads to interesting effects on delayed-proton spectra that follow the β decays of N = 81 precursors and on the α-decay half-lives of neutron-deficient lead isotopes. Pronounced peaks were observed in the proton spectra of ¹⁴⁷Dy, ¹⁴⁹Er, and ¹⁵¹Yb. Experimental decomposition of these spectra showed that this structure is due to a low density of 1/2 and 3/2 states at excitation energies of ∼ 4.5 MeV in the respective N = 82 β-decay daughters. In the case of the light lead nuclei, ^{186,188,190,192}Pb, it was determined that, contrary to the expectation of a shell effect at Z = 82, their α-decay rates are faster than those of neighboring mercury isotopes. Midway between the N = 82 and N = 126 shells it would appear that the Z = 82 configuration is not magic

[en] The Fragment Mass Analyzer (FMA) at the ATLAS accelerator has been operational for about one year. During that period a number of test runs and experiments have been carried out. The test runs have verified that the ion optics of the FMA are essentially as calculated. A brief facility description is followed by recent experimental results

[en] The experimental program at the Fragment Mass Analyzer (FMA) at the ATLAS accelerator is well under way. Experiments have been carried out at the target position and at the focal plane. After a brief facility description, some recent experimental results are presented

[en] The Fragment Mass Analyzer (FMA) at the ATLAS accelerator has been operational for about one year. During that period a number of test runs and experiments have been carried out. The test runs have verified that the ion optics of the FMA are essentially as calculated. A brief facility description is followed by recent experimental results

[en] Experimental and theoretical studies of exotic nuclei, i.e., very short-lived nuclei far away from the valley of stability in the chart of nuclides, present a unique and important way to gain general understanding of the atomic nucleus and the governing interactions of its constituents. There is an intriguing interplay of strong, weak, and Coulomb interaction, yet the contributions from all fundamental forces (except gravitation) are integrated in the mass of a nucleus. This makes the mass one of its key properties, allowing to study nuclear structure and basic interactions. Studying exotic nuclei is challenging since they need to be produced first, they are short-lived (many of them have half-lives of only few seconds or even far below), they can only be produced in small quantities, and often the interesting ones are accompanied by a full zoo of other, less exotic and more abundantly produced nuclei. Therefore, powerful separation methods are needed to deal with huge amounts of non-interesting 'by-products' and simultaneously obtain reliable results even for the few nuclei of interest. Moreover, the goal to extract information on basic interactions and nuclear structure requires high accuracies despite low statistics. In this work, improvements and measurements have been implemented and performed at two experiments at different accelerator facilities. In both experiments, a Multiple-Reflection Time-of-Flight Mass-Spectrometer (MR-TOF-MS), which has been build at Gießen University, is used. At the FRS Ion Catcher (FRS-IC) at GSI, Darmstadt, the improvements enabled unprecedented mass accuracies; at TRIUMF’s Ion Trap for Atomic and Nuclear sciences (TITAN) at TRIUMF, Vancouver, Canada, a novel method for mass separation was used to facilitate measurement with previously unknown nuclei. Within these measurements, a new isotope was discovered. This is the first discovery of a new isotope using a time-of-flight mass spectrometer. This demonstrates the advance of the frontier in mass measurements of exotic nuclei and the understanding of nuclear structure at the extremes. At the FRS-IC, several hardware and software elements have been upgraded. The new slow control system at the FRS-IC is running stable and ready to control, monitor and log existing and also various planned extensions of the detector setup. A procedure for systematically tuning the ion optics to unprecedented mass resolving powers R = m/∆m = 1 000 000 and beyond has been established. This enabled the measurement of several exotic nuclei with mass numbers around A = 70 close to the N = Z line. Among these measurements was the first direct mass measurements of 69-As, with only 10 events and with reduced uncertainty compared to the average of the previous indirect measurements. For one measued molecule, an accuracy of δm/m = 1.7 × 10e${}^{-<!--\; ???\; -->8}$ was reached, which is the highest accuracy for MR-TOF-MS world-wide. The techniques applied at the FRS-IC have since been used at the TITAN MR-TOF-MS as well, also there leading to improved mass resolving powers. For TITAN, mass-selective re-trapping was characterized and for the first time used with exotic nuclei, enabling the direct measurement of 2 new and 2 improved ground state masses for neutron deficient Yb isotopes, the first measurement of the excitation energy of the J${}^{\mathrm{\pi <!--\; ??\; -->}}$ = 11/2${}^{-<!--\; ???\; -->}$ isomeric state in 151-Yb and the indirect determination of 11 more ground state masses connected via α- and p-decays to two of the newly measured masses. The measurement of the mass of 150-Yb is at the same time the first discovery of a new isotope with an MR-TOF-MS. The direct ground state mass measurements of the Yb isotopes and the subsequent determination of masses of Lu isotopes have established the N = 82 neutron shell closure farthest from the valley of β-stability with unmodified shell gap; the shell structure far from the valley of stability is a key question of modern nuclear physics. The measurement of the J${}^{\mathrm{\pi <!--\; ??\; -->}}$ = 11/2${}^{-<!--\; ???\; -->}$ isomeric state excitation energy extends a series of constant excitation energies in these odd N = 81 states, which could now be explained by deformation of the ground and isomeric states in collaboration with theorists employing state-of-the-art nuclear mean field.

[en] Progress is reported for a collaborative program, involving researchers from the Lawrence Berkeley and Oak Ridge National Laboratories, which has now been in progress at the SuperHILAC OASIS on-line facility for more than two years. In these investigations properties of short lived nuclei near the N = 82 neutron shell have been studied, their decays being assayed with particle, gamma ray, x ray, and positron detectors. Nuclides investigated so far were produced in ⁵⁸Ni bombardments of ⁹⁶Ru, ⁹⁴Mo, and ⁹²Mo. The focus of the study has been primarily two-fold: (1) to gain insight into the nature of the sharp peaks seen in the delayed proton spectra that accompany the beta decays of N = 81 even Z precursors, and (2) to investigate low lying states in nuclei near N = 82, levels whose structures should be describable by shell model analyses. 9 refs., 2 figs

[en] The Fragment Mass Analyzer (FMA) at the ATLAS accelerator has been operational for about one year. During that period a number of test runs and experiments have been ran. The test runs have verified that the ion optics of the FMA are essentially as calculated. Experiments have been carried out on sub-Coulomb transfer reactions, alpha decay of neutron-deficient Pt isotopes. in-beam gamma rays from^202--204Rn, and the study of yrast isomers in ¹⁵¹Yb. Recent results are presented, along with a brief facility desorption

[en] We have been involved in the investgation of nuclear structure properties of nuclei close to the proton drip line. In these studies we have used on-line isotope separators at Oak Ridge (UNISOR) and Berkeley (OASIS), the ORNL velocity filter, and a fast helium-gas-jet transport system at the LBL 88-in. cyclotron. We describe briefly three areas of our research that have dealt with particle decays: 1. α-decay in medium-weight nuclei, 2. α-decay rates for even-even isotopes, and 3. β-delayed-proton decay of N = 81 precursors. (orig.)

[en] Unexpected similarities between the superdeformed bands found recently in many nuclei of the mass A ∼ 150 and A ∼ 190 regions and the physical sense of this discovery are discussed. These similarities manifest themselves through the existence of nearly identical sequences of transitions belonging to two neighboring nuclei, and by now numerous nuclear pairs manifesting this feature have been found. The underlying microscopic mechanism is traced back to two independent effects: a readjustment of nuclear deformation diminishing the role of alignment of the least bound nucleus, and, the pseudospin symmetry, responsible for an approximate decoupling of the orbital and the intrinsic (pseudo) spin-degrees of freedom. 9 figs