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The shell structure of atomic nuclei is associated with 'magic numbers' and originates in the nearly independent motion of neutrons and protons in a mean potential generated by all nucleons. During ?+-decay, a proton transforms into a neutron in a previously not fully occupied orbital, emitting a positron-neutrino pair with either parallel or antiparallel spins, in a Gamow-Teller or Fermi transition, respectively. The transition probability, or strength, of a Gamow-Teller transition depends sensitively on the underlying shell structure and is usually distributed among many states in the neighbouring nucleus. Here we report measurements of the half-life and decay energy for the decay of 100Sn, the heaviest doubly magic nucleus with equal numbers of protons and neutrons. In the ?-decay of 100Sn, a large fraction of the strength is observable because of the large decay energy. We determine the largest Gamow-Teller strength so far measured in allowed nuclear ?-decay, establishing the 'superallowed' nature of this Gamow-Teller transition. The large strength and the low-energy states in the daughter nucleus, 100In, are well reproduced by modern, large-scale shell model calculations. [ABSTRACT FROM AUTHOR]

Heavy neutron-rich nuclei have been populated through the relativistic fragmentation of a $\ensuremath ^{208}_{\ 82}{\rm Pb}$ beam at $\ensuremath E/A = 1$ GeV on a $\ensuremath 2.5 {\rm g/cm^2}$ thick Be target. The synthesised nuclei were selected and identified in-flight using the fragment separator at GSI. Approximately 300 ns after production, the selected nuclei were implanted in an $\ensuremath \sim 8$ mm thick perspex stopper, positioned at the centre of the RISING $\ensuremath \gamma$ -ray detector spectrometer array. A previously unreported isomer with a half-life $\ensuremath T_{1/2} = 163(5)$ ns has been observed in the N = 126 closed-shell nucleus $\ensuremath ^{205}_{\ 79}{\rm Au}$ . Through $ \gamma$ -ray singles and $ \gamma$ - $ \gamma$ coincidence analysis a level scheme was established. The comparison with a shell model calculation tentatively identifies the spin-parity of the excited states, including the isomer itself, which is found to be $\ensuremath I^{\pi} = (19/2^+)$ . [ABSTRACT FROM AUTHOR]

Heavy neutron-rich nuclei were populated via relativistic energy fragmentation of a E/A = 1 GeV208Pb beam. The nuclei of interest were selected and identified by a fragment separator and then implanted in a passive plastic stopper. Delayed γ rays following internal isomeric decays were detected by the RISING array. Experimental information was obtained on a number of nuclei with Z = 73-80 (Ta-Hg), providing new information both on the prolate-oblate transitional region as well as on the N = 126 closed shell nuclei. [ABSTRACT FROM AUTHOR]

Nuclear spectroscopy using radioactive isotope beams requires dedicated set-ups. At the SIS/FRS facility at GSI exotic beams at relativistic energies were employed for Coulomb excitation and secondary fragmentation experiments with the fast beam RISING set-up. Shell evolution far off stability, pn-pairing, symmetries and nuclear shapes were studied in nuclei ranging from 36Ca to 136Nd. In another Ge-detector configuration a series of g-factor experiments was performed. Recently the compact detector arrangement of RISING -- providing about 15% full energy efficiency -- went into operation. Seniority isomers in medium heavy nuclei at the proton drip line have been investigated as well as new isomers found in neutron rich nuclei, e.g. 204Pt. Most recently the decay properties of 100Sn were investigated successfully. At future FAIR/GSI the Super-FRS facility within the NUSTAR project will provide an enormously enlarged variety of exotic beams. To fully exploit these beams the HISPEC/DESPEC project aims to develop, build and operate optimized experimental set-ups. Based on the experience with RISING novel particle identification and tracking detectors will be employed. For in-beam γ detection AGATA detectors are foreseen as well as a dedicated compact Ge tracking and imaging array for decay experiments. Well before the Super-FRS facility will become operational, detectors developed for HISPEC/DESPEC will be commissioned and employed for experimental campaigns within the PRESPEC project at the FRS facility at GSI. [ABSTRACT FROM AUTHOR]

Decays of neutron-rich A ~ 190 nuclei have been studied following projectile fragmentation of a 208Pb beam on a 9Be target at the GSI Fragment Separator. Gamma-ray decays from previously reported isomeric states in 188Ta, 190W and 192,193Re were used as internal calibrations for the particle identification analysis, together with the identification of previously unreported isomeric decays in 189Ta and 191W. The current work also identifies β-delayed γ rays following the decay of 188Ta to 188W for the first time. [ABSTRACT FROM AUTHOR]

Relativistic fragmentation of 208Pb has been used to produce excited states in neutron-rich nuclei with N ≈ 126. Spectroscopic information for a range of nuclei has been obtained through observing delayed γ-ray emissions from isomeric states. Preliminary results for 203,204Pt nuclei are presented. For the first time, excited states have been observed in 203Pt and 204Pt. The yrast structure of 204Pt up to spin-parity, Iπ = (10+) has been tentatively inferred from the internal decay of two isomeric states. [ABSTRACT FROM AUTHOR]

Preliminary results from the first experiment of the Stopped Beam RISING campaign are presented. The relativistic projectile fragmentation of a 750 MeV/u beam of 107Ag populated isomeric states in very neutron deficient nuclei at the proton dripline around mass 80-90. Nuclei were unambiguously identified using the FRagment Separator (FRS) and its ancillary detectors located at GSI. The ions produced were slowed down from relativistic energies by means of an Al degrader and implanted in the centre of the high-efficiency Stopped RISING array. This allowed the identification of new excited states in the N = Z = 43 nucleus, 86Tc, populated following the de-excitation of a microsecond isomer. Preliminary results of this analysis, as well as previously unobserved isomeric states in 87,88Tc, are reported. [ABSTRACT FROM AUTHOR]

Within the RISING (Rare ISotope INvestigations @ GSI) Collaboration at GSI, g factor measurements have been performed on isomeric states in neutron-rich isotopes approaching 132Sn and in the neutron deficient Pb-region (the g-RISING campaign). We present the experimental technique and some typical aspects related to such studies on relativistic beams selected with the FRS fragment separator. First results are presented for the (19/2+) 4.5 µs isomeric state in 127Sn, which has been produced by means of fission of a relativistic 238U beam on the one hand, and by the fragmentation of a relativistic 136Xe beam on the other hand. Spin-alignment has been observed in both reactions. It was the first time that spin-alignment has been established in a relativistic fission reaction. [ABSTRACT FROM AUTHOR]

Breakup reactions were used to study the ground-state configuration of the neutron-rich isotope 23O. The 22O fragments produced in one-nucleon removal from 23O at 938 MeV/nucleon in a carbon target were detected in coincidence with de-exciting γ rays, allowing to discern between 22O ground-state and excited-states contributions. From the comparison of exclusive experimental momentum distributions for the one-neutron removal channel to theoretical momentum distributions calculated in an Eikonal model for the knockout process, and spin and parity assignment of Iπ = 1/2+ was deduced for the 23O ground state. This result solved the existent experimental discrepancy. [ABSTRACT FROM AUTHOR]

The projectile fragmentation of a 92 Mo beam onto a beryllium target at an incident energy of 500 A MeV has been studied at the high-resolution spectrometer FRS at GSI. The isotopic production cross-sections of the projectile fragments produced in the reaction have been determined. The data have been compared to the empirical parameterisation, EPAX, and to a microscopic nuclear reaction model, ABRABLA. [ABSTRACT FROM AUTHOR]

Relativistic projectile fragmentation of208Pb has been used to produce isomers in neutron-rich,A˜ 190 nuclides. A forward-focusing spectrometer provided ion-by-ion mass and charge identification. The detection of ?-rays emitted by stopped ions has led to the assignment of isomers in188Ta,190W,192Re,193Re,195Os,197Ir,198Ir,200Pt,201Pt,202Pt and203Au, with half-lives ranging from approximately 10 ns to 1 ms. Tentative isomer information has been found also for174Er,175Er,185Hf,191Re,194Re and199Ir. In most cases, time-correlated, singles ?-ray events provided the first spectroscopic data on excited states for each nuclide. In200Pt and201Pt, the assignments are supported by ?-? coincidences. Isomeric ratios provide additional information, such as half-life and transition energy constraints in particular cases. The level structures of the platinum isotopes are discussed, and comparisons are made with isomer systematics. [ABSTRACT FROM AUTHOR]

The neutron transfer in a very heavy asymmetric nuclear system, in 206Pb + 118Sn has been measured using particle-γ coincidence techniques with position-sensitive detectors, 5 EUROBALL-Cluster detectors (EB) and the Heidelberg-Darmstadt Nal-CIRYSTAL BALL (CB). The fragments are identified via the known γ-decays of the lowest excited states using the high resolution of EB. Using the unique feature of the set-up with the CB, transfer to well-defined final channels with known quantum numbers is selected using the high-efficiency multiplicity filter of the CB with no second γ-ray, i. e. without feeding. The enhancement in the two-neutron transfer is deduced, for population of the low-lying super-fluid 2+ states in 120Sn and 116Sn, while the 2n-transition remains in the ground state for the recoiling 20XPb-nuclei Large enhancements up to EF ≃ 10³ are observed. This is the first observation of neutron pair-transfer enhancement for a heavy nuclear binary system with superfluid properties with experimentally separated levels. [ABSTRACT FROM AUTHOR]

At energies below the Coulomb barrier, neutron transfer and Coulomb excitation have been measured in a very heavy asymmetric nuclear system, in206Pb +118Sn. These are semi-magic nuclei showing super-fluid properties. Particle-γ coincidence techniques using 5 Euroball Cluster detectors (EB), combined in a set-up with the Heidelberg-Darmstadt NaI Crystal Ball (CB), have been used. Position-sensitive detectors allowed the observation of scattering processes covering angles from 110 up to 150 degrees. The fragments are identified via the known γ-decays of the lowest excited states using the high resolution of EB. Using the unique feature of the set-up with the CB, transfer to well-defined final channels with known quantum numbers is selected using the high-efficiency multiplicity filter of the CB with no second γ-ray, i.e. without feeding. The data are analysed using the semi-classical approach and transfer probabilities are obtained. Coulomb excitation has been analysed using known transition probabilities. The enhancement is deduced for the two-neutron transfer populating the low-lying super-fluid 2+ states in120Sn and116Sn, while the 2n transition remains in the ground state for the20NPb nuclei. Large enhancements up to EF ≃ 103 are observed. This is the first observation of neutron pair transfer enhancement for a heavy nuclear binary system with super-fluid properties with experimentally separated levels. The calculations with microscopic 2-neutron wave functions, with configuration mixing over six shell model configurations and using the coupled reaction channels approach, reproduce well the observed probabilities and the enhancement. [ABSTRACT FROM AUTHOR]

The neutron-rich nucleus 117Rh was synthesized in the fission of a relativistic 238U beam produced at the GSI laboratory in Darmstadt, Germany. An isomeric state with t1/2 = 138(17) ns decaying by a single y ray was observed, providing the first information on the excited states in this nucleus. The experimental data are discussed in terms of systematics and interpreted by using the Woods-Saxon deformed shell model and triaxial-rotor-plus-particle calculations. The origin of the isomer is explained as being due to a hindered E2 transition to the ground state. [ABSTRACT FROM AUTHOR]

New measurements of the interaction cross sections of 22,230 at 900A MeV performed at the GSI, Darmstadt are reported that address the unsolved puzzle of the large cross section previously observed for 230. The matter radii for these oxygen isotopes extracted through a Glauber model analysis are in good agreement with the new predictions of the ab initio coupled-cluster theory reported here. They are consistent with a 220 + neutron description of 230 as well. [ABSTRACT FROM AUTHOR]

The interaction cross sections of 32-35Mg at 900A MeV have been measurmed using the fragment separator at GSI. The deviation from the r0A1/3 trend is slightly larger for 35Mg, signaling the possible formation of a longer tail in the neutron distribution for 35Mg. The radii extracted from a Glauber model analysis with Fermi densities are consistent with models predicting the development of neutron skins. [ABSTRACT FROM AUTHOR]

Abstract: We report on the g factor measurement of the isomeric state (, ) in the neutron-rich 126Sn nucleus. The nucleus was produced by the fission of a relativistic 238U beam and reaction products were selected by the FRS fragment separator at GSI. For the first time, spin-alignment was observed after relativistic fission. It was used to deduce the g factor of the isomeric state, , from the measured perturbed angular distribution of its γ decay using the RISING Cluster detectors. The observed value confirms the suggested dominant configuration, which has been proposed for the isomers in neutron-rich Sn isotopes. The failure of the g factor additivity rule and the importance of core polarization evolution with increasing distance from the doubly-magic 132Sn is discussed. The first observation of 18(8)% of spin-alignment produced by the relativistic fission of a 238U beam paves the way to study moments of neutron-rich (sub-)microsecond isomers, which are difficult to align by other means. [Copyright &y& Elsevier]

Heavy neutron-rich nuclei have been populated through the relativistic fragmentation of a $\ensuremath ^{208}_{\ 82}{\rm Pb}$ beam at $\ensuremath E/A = 1$ GeV on a $\ensuremath 2.5 {\rm g/cm^2}$ thick Be target. The synthesised nuclei were selected and identified in-flight using the fragment separator at GSI. Approximately 300 ns after production, the selected nuclei were implanted in an $\ensuremath \sim 8$ mm thick perspex stopper, positioned at the centre of the RISING $\ensuremath \gamma$ -ray detector spectrometer array. A previously unreported isomer with a half-life $\ensuremath T_{1/2} = 163(5)$ ns has been observed in the N = 126 closed-shell nucleus $\ensuremath ^{205}_{\ 79}{\rm Au}$ . Through $ \gamma$ -ray singles and $ \gamma$ - $ \gamma$ coincidence analysis a level scheme was established. The comparison with a shell model calculation tentatively identifies the spin-parity of the excited states, including the isomer itself, which is found to be $\ensuremath I^{\pi} = (19/2^+)$ . [ABSTRACT FROM AUTHOR]

Abstract: The first excited states in 54,56,58Cr were populated by Coulomb excitation at relativistic energies and γ rays were measured using the RISING setup at GSI. For 56Cr and 58Cr the values relative to the previously known value for 54Cr are determined as 8.7(3.0) and 14.8(4.2) W.u., respectively. The results are consistent with a subshell closure at neutron number which was already indicated by the higher energy of the state in 56Cr. Recent large-scale shell model calculations using effective interactions reproduce the trend in the excitation energies, but fail to account for the minimum in the values at . [Copyright &y& Elsevier]