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The pygmy dipole resonance has been studied in the proton-magic nucleus 124 Sn with the (α, α ′ γ) coincidence method at Eα = 136 MeV. The comparison with results of photon-scattering experiments reveals a splitting into two components with different structure: one group of states which is excited in (α, α ′ γ) as well as in (γ, γ ′ ) reactions and a group of states at higher energies which is only excited in (γ, γ ′ ) reactions. Calculations with the self-consistent relativistic quasiparticle timeblocking approximation and the quasi-particle phonon model are in qualitative agreement with the experimental results and predict a low-lying isoscalar component dominated by neutron-skin oscillations and a higher-lying more isovector component on the tail of the giant dipole resonance.PACS numbers: 24.30.Cz, Collective phenomena are a common feature of strongly interacting many-body quantum systems directly linked to the relevant effective interactions. Atomic nuclei also show collective behavior. One example is given by the giant resonances, which have been investigated intensively using different experimental methods, see e.g., [1]. The isovector electric giant dipole resonance (IVGDR) has been the first giant resonance to be observed in atomic nuclei. Ever since it has been of particular interest, because collective E1 response is related to symmetry breaking between neutrons and protons. In recent years, the so-called pygmy dipole resonance (PDR) [2][3][4], a concentration of electric dipole strength energetically below the IVGDR, has been studied intensively in various nuclei. Within most modern microscopic nuclear structure models, this new excitation mode is related to the oscillation of a neutron skin against a symmetric proton-neutron core with isospin T = 0; for an overview see the recent review by Paar et al. [5]. Consequently, one expects an increase of the PDR strength approaching isotopes with extreme neutron-to-proton ratios. Experiments on radioactive neutron-rich nuclei seem to support this assumption [6][7][8][9][10][11]. If this picture holds, the strength of the PDR is related to the thickness of the neutron skin and the density dependence of the symmetry energy of nuclear matter [7,12]. The PDR thus permits experimental access to these properties. However, more consistent systematic investigations and especially more constraints on the structure of the PDR are mandatory, such as the experiments presented in this Letter, in order to confirm this picture.Up to now only experiments on stable nuclei allow more detailed investigations of the PDR which yield additional observables in order to understand the underlying structure of this new excitation mode. In nuclear resonance fluorescence (NRF) experiments the systematics of the PDR as well as its fragmentation and fine-structure can be studied [3,4,[13][14][15][16][17][18][19] up to the particle threshold. The mean excitation energy and the summed transition strength B(E1)↑ (of up to 1% of the isovector energy weighted sum rule) show a smooth variat...

Abstract-Recoil decay tagging (RDT) is a very powerful method for the spectroscopy of exotic nuclei. RDT is a delayed coincidence technique between detectors usually at the target position and at the focal plane of a spectrometer. Such measurements are often limited by dead time. This paper describes a novel triggerless data acquisition method, which is being developed for the gamma recoil electron alpha tagging (GREAT) spectrometer, that overcomes this limitation by virtually eliminating dead time.Our solution is a total data readout (TDR) method where all channels run independently and are associated in software to reconstruct events. The TDR method allows all the data from both target position and focal plane to be collected with practically no dead-time losses. Each data word is associated with a timestamp generated from a global 100-MHz clock. Events are then reconstructed in real time in the event builder using temporal and spatial associations defined by the physics of the experiment.

Superheavy Element Flerovium (Element 114) Is a Volatile MetalAccess to the published version may require subscription. Superheavy Element Flerovium (Element 114) is a Volatile MetalAlexander Yakushev †, , Jacklyn M. ABSTRACT: The electron shell structure of superheavy elements, i.e., elements with atomic number Z ≥ 104, is influenced by strong relativistic effects caused by the high Z. Early atomic calculations on element 112 (copernicium, Cn) and element 114 (flerovium, Fl) having closed and quasiclosed electron shell configurations of 6d 10 7s 2 and 6d 10 7s 2 7p 1/2 , respectively, predicted them to be noble gas-like due to very strong relativistic effects on the 7s and 7p 1/2 valence orbitals. Recent fully relativistic calculations studying Cn and Fl in different environments suggest them to be less reactive compared to their lighter homologs in the groups, but still exhibiting a metallic character. Experimental gassolid chromatography studies on Cn have, indeed, revealed a metal-metal bond formation with Au. In contrast to this, for Fl, the formation of a weak bond upon physisorption on a Au surface was inferred from first experiments. Here, we report on a gas-solid chromatography study of the adsorption of Fl on a Au surface. Fl was produced in the nuclear fusion reaction 244 Pu( 48 Ca, 3-4n) 288,289 Fl and was isolated in-flight from the primary 48 Ca beam in a physical recoil separator. The adsorption behavior of Fl, its nuclear α-decay product Cn, their lighter homologs in groups 14 and 12, i.e., Pb and Hg, and the noble gas Rn were studied simultaneously by isothermal gas chromatography and thermochromatography. Two Fl atoms were detected. They adsorbed on a Au surface at room temperature in the first, isothermal part, but not as readily as Pb and Hg. The observed adsorption behavior of Fl points to a higher inertness compared to its nearest homolog in the group, Pb. However, the measured lower limit for the adsorption enthalpy of Fl on a Au surface points to the formation of a metal-metal bond of Fl with Au. Fl is the least reactive element in the group, but still a metal.

A long-standing prediction of nuclear models is the emergence of a region of long-lived, or even stable, superheavy elements beyond the actinides. These nuclei owe their enhanced stability to closed shells in the structure of both protons and neutrons. However, theoretical approaches to date do not yield consistent predictions of the precise limits of the 'island of stability'; experimental studies are therefore crucial. The bulk of experimental effort so far has been focused on the direct creation of superheavy elements in heavy ion fusion reactions, leading to the production of elements up to proton number Z = 118 (refs 4, 5). Recently, it has become possible to make detailed spectroscopic studies of nuclei beyond fermium (Z = 100), with the aim of understanding the underlying single-particle structure of superheavy elements. Here we report such a study of the nobelium isotope 254No, with 102 protons and 152 neutrons--the heaviest nucleus studied in this manner to date. We find three excited structures, two of which are isomeric (metastable). One of these structures is firmly assigned to a two-proton excitation. These states are highly significant as their location is sensitive to single-particle levels above the gap in shell energies predicted at Z = 114, and thus provide a microscopic benchmark for nuclear models of the superheavy elements.