A measurement of the reduced transition probability for the excitation of the ground state to the first 2 þ state in 104 Sn has been performed using relativistic Coulomb excitation at GSI. 104 Sn is the lightest isotope in the Sn chain for which this quantity has been measured. The result is a key point in the discussion of the evolution of nuclear structure in the proximity of the doubly magic nucleus 100 Sn. The properties of many composite quantum objects that represent building blocks of matter, such as hadrons, atomic nuclei, atoms, and molecules are governed by energy gaps between quantum states which originate in the forces between their fermionic constituents. In the case of atomic nuclei, the energy gaps manifest themselves by the existence of specific stable isotopes. These include, e.g., the double shell-closure nuclei 4 He, 16 O,40;48 Ca, and 208 Pb, which are particularly robust against particle separation and intrinsic excitation. The -unstable isotopes 56 Ni, 78 Ni, and 100;132 Sn are also expected to correspond to double shell closures. However, data for 78 Ni and 100 Sn are scarce due to their exotic neutron-to-proton ratios. Therefore, there is considerable interest in finding more proof for the magicity of these isotopes. In addition, the single particle energies relative to 100 Sn are largely unknown experimentally. Data are limited to the energy splitting between the two lowest-energy orbitals [1,2] while extrapolations from nearby nuclei are available with a typical uncertainty of a few hundred keV for the orbitals of higher energy [3]. Since 100 Sn is predicted to be a doubly magic nucleus, it would provide an approximately inert core on top of which simple excitations can be formed by adding few particles or holes. For this reason, it presents an ideal testing ground for fundamental nuclear models. Another cause for increased interest in nuclear structure in this region comes from the rp process of nuclear synthesis [4]. It has been concluded recently that this reaction sequence comes to an end near 100 Sn [4]. In addition, 100 Sn itself is expected to be the heaviest self-conjugate PRL 110,

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In the EXILL campaign a highly efficient array of high purity germanium (HPGe) detectors was operated at the cold neutron beam facility PF1B of the Institut Laue-Langevin (ILL) to carry out nuclear structure studies, via measurements of γ-rays following neutron-induced capture and fission reactions. The setup consisted of a collimation system producing a pencil beam with a thermal capture equivalent flux of about 108 n s−1cm−2 at the target position and negligible neutron halo. The target was surrounded by an array of eight to ten anti-Compton shielded EXOGAM Clover detectors, four to six anti-Compton shielded large coaxial GASP detectors and two standard Clover detectors. For a part of the campaign the array was combined with 16 LaBr3:(Ce) detectors from the FATIMA collaboration. The detectors were arranged in an array of rhombicuboctahedron geometry, providing the possibility to carry out very precise angular correlation and directional-polarization correlation measurements. The triggerless acquisition system allowed a signal collection rate of up to 6 × 105 Hz. The data allowed to set multi-fold coincidences to obtain decay schemes and in combination with the FATIMA array of LaBr3:(Ce) detectors to analyze half-lives of excited levels in the pico- to microsecond range. Precise energy and efficiency calibrations of EXILL were performed using standard calibration sources of 133Ba, 60Co and 152Eu as well as data from the reactions 27Al(n,γ)28Al and 35Cl(n,γ)36Cl in the energy range from 30 keV up to 10 MeV.

The coupling of the giant quadrupole resonance to valence-space configurations is shown to be the origin of the formation of low-lying quadrupole-collective structures in vibrational nuclei with symmetric and mixed-symmetric character with respect to the proton-neutron degree of freedom. For the first time experimental evidence for this picture is obtained from electron- and proton scattering experiments on the nucleus ^{92}Zr that are sensitive to the relative phase of valence-space amplitudes by quantum interference.

The high-spin structure of the 105 Ag nucleus has been studied by using the 100 Mo( 10 B, 5n) 105 Ag reaction to search for chiral doublet bands based on the three-quasiparticle πg 9/2 ν(h 11/2 ) 2 configuration. The level scheme of 105 Ag has been extended. New bands were found and the placement of the yrast πg 9/2 ν(h 11/2 ) 2 band was corrected. No side band to the yrast πg 9/2 ν(h 11/2 ) 2 band could be found in the present experiment. This observation indicates that the γ -soft shape in the 106 Ag changed to a more γ -rigid axially symmetric shape in the yrast 105 Ag configuration. However, a new pair of bands was observed to show the expected properties of a chiral doublet structure.