305 research outputs found

    Laser assisted decay spectroscopy at the CRIS beam line at ISOLDE

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    The new collinear resonant ionization spectroscopy (Cris) experiment at Isolde, Cernuses laser radiation to stepwise excite and ionize an atomic beam for the purpose of ultra-sensitive detection of rare isotopes and hyperfine structure measurements. The technique also offers the ability to purify an ion beam that is contaminated with radioactive isobars, including the ground state of an isotope from its isomer. A new program using the Cristechnique to select only nuclear isomeric states for decay spectroscopy commenced last year. The isomeric ion beam is selected using a resonance within its hyperfine structure and subsequently deflected to a decay spectroscopy station. This consists of a rotating wheel implantation system for alpha and beta decay spectroscopy, and up to three high purity germanium detectors for gamma-ray detection. This paper gives an introduction to the Cristechnique, the current status of the laser assisted decay spectroscopy set-up and recent results from the experiment in November 201

    A new technique for elucidating β\beta-decay schemes which involve daughter nuclei with very low energy excited states

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    A new technique of elucidating β\beta-decay schemes of isotopes with large density of states at low excitation energies has been developed, in which a Broad Energy Germanium (BEGe) detector is used in conjunction with coaxial hyper-pure germanium detectors. The power of this technique has been demonstrated on the example of 183Hg decay. Mass-separated samples of 183Hg were produced by a deposition of the low-energy radioactive-ion beam delivered by the ISOLDE facility at CERN. The excellent energy resolution of the BEGe detector allowed γ\gamma rays energies to be determined with a precision of a few tens of electronvolts, which was sufficient for the analysis of the Rydberg-Ritz combinations in the level scheme. The timestamped structure of the data was used for unambiguous separation of γ\gamma rays arising from the decay of 183Hg from those due to the daughter decays

    In-gas-cell laser ionization spectroscopy in the vicinity of 100Sn: Magnetic moments and mean-square charge radii of N=50-54 Ag

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    In-gas-cell laser ionization spectroscopy studies on the neutron deficient 97-101Ag isotopes have been performed with the LISOL setup. Magnetic dipole moments and mean-square charge radii have been determined for the first time with the exception of 101Ag, which was found in good agreement with previous experimental values. The reported results allow tentatively assigning the spin of 97,99Ag to 9/2 and confirming the presence of an isomeric state in these two isotopes, whose collapsed hyperfine structure suggests a spin of 1/2 . The effect of the N=50 shell closure is not only manifested in the magnetic moments but also in the evolution of the mean-square charge radii of the isotopes investigated, in accordance with the spherical droplet model predictions

    Decay-assisted collinear resonance ionization spectroscopy: Application to neutron-deficient francium

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    This paper reports on the hyperfine-structure and radioactive-decay studies of the neutron-deficient francium isotopes 202206^{202-206}Fr performed with the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at the ISOLDE facility, CERN. The high resolution innate to collinear laser spectroscopy is combined with the high efficiency of ion detection to provide a highly-sensitive technique to probe the hyperfine structure of exotic isotopes. The technique of decay-assisted laser spectroscopy is presented, whereby the isomeric ion beam is deflected to a decay spectroscopy station for alpha-decay tagging of the hyperfine components. Here, we present the first hyperfine-structure measurements of the neutron-deficient francium isotopes 202206^{202-206}Fr, in addition to the identification of the low-lying states of 202,204^{202,204}Fr performed at the CRIS experiment.Comment: Accepted for publication with Physical Review

    Laser spectroscopy of francium isotopes at the borders of the region of reflection asymmetry

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    The magnetic dipole moments and changes in mean-square charge radii of the neutron-rich 218m,219,229,231Fr^{218m,219,229,231}\text{Fr} isotopes were measured with the newly-installed Collinear Resonance Ionization Spectroscopy (CRIS) beam line at ISOLDE, CERN, probing the 7s 2S1/27s~^{2}S_{1/2} to 8p 2P3/28p~^{2}P_{3/2} atomic transition. The δr2A,221\delta\langle r^{2}\rangle^{A,221} values for 218m,219Fr^{218m,219}\text{Fr} and 229,231Fr^{229,231}\text{Fr} follow the observed increasing slope of the charge radii beyond N = 126N~=~126. The charge radii odd-even staggering in this neutron-rich region is discussed, showing that 220Fr^{220}\text{Fr} has a weakly inverted odd-even staggering while 228Fr^{228}\text{Fr} has normal staggering. This suggests that both isotopes reside at the borders of a region of inverted staggering, which has been associated with reflection-asymmetric shapes. The g(219Fr)=+0.69(1)g(^{219}\text{Fr}) = +0.69(1) value supports a π1h9/2\pi 1h_{9/2} shell model configuration for the ground state. The g(229,231Fr)g(^{229,231}\text{Fr}) values support the tentative Iπ(229,231Fr)=(1/2+)I^{\pi}(^{229,231}\text{Fr}) = (1/2^{+}) spin, and point to a πs1/21\pi s_{1/2}^{-1} intruder ground state configuration.Comment: Accepted for publication with Physical Review

    Shape Isomerism at N = 40: Discovery of a Proton Intruder in 67Co

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    The nuclear structure of 67Co has been investigated through 67Fe beta-decay. The 67Fe isotopes were produced at the LISOL facility in proton-induced fission of 238U and selected using resonant laser ionization combined with mass separation. The application of a new correlation technique unambiguously revealed a 496(33) ms isomeric state in 67Co at an unexpected low energy of 492 keV. A 67Co level scheme has been deduced. Proposed spin and parities suggest a spherical (7/2-) 67Co ground state and a deformed first excited (1/2-) state at 492 keV, interpreted as a proton 1p-2h prolate intruder state.Comment: 4 pages, 5 figures, preprint submitted to Physical Review Letter

    Towards nuclear structure with radioactive muonic atoms The nuclear charge radius of radioactive isotopes from measurements of muonic X-rays

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    The muX project at the Paul Scherrer Institut aims to perform highresolution muonic atom X-ray spectroscopy for the extraction of nuclear charge radii of radioactive isotopes that can be handled only in microgram quantities. Measurements of the absolute charge radii of high-Z radioactive elements are complementary to the measurements of relative differences in mean-square radii along the isotopic chain available from laser spectroscopy. One of the major limitations of atomic structure calculations is related with the uncertainty of the nuclear charge radius. This is the case for the extraction of the Weinberg angle from atomic parity violation in 226Ra. A new approach to solve previous limitations of muonic atom X-ray spectroscopy experiments is the application of multiple muon transfer reactions in a high-pressure hydrogen gas cell with a small admixture of deuterium. The validity of this method has been demonstrated with a measurement with only 5 μg of gold

    Precision Mass Measurements of 129-131Cd and Their Impact on Stellar Nucleosynthesis via the Rapid Neutron Capture Process

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    Masses adjacent to the classical waiting-point nuclide 130Cd have been measured by using the Penning- trap spectrometer ISOLTRAP at ISOLDE/CERN. We find a significant deviation of over 400 keV from earlier values evaluated by using nuclear beta-decay data. The new measurements show the reduction of the N = 82 shell gap below the doubly magic 132Sn. The nucleosynthesis associated with the ejected wind from type-II supernovae as well as from compact object binary mergers is studied, by using state-of-the-art hydrodynamic simulations. We find a consistent and direct impact of the newly measured masses on the calculated abundances in the A = 128 - 132 region and a reduction of the uncertainties from the precision mass input data

    Early onset of ground-state deformation in the neutron-deficient polonium isotopes

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    In-source resonant ionization laser spectroscopy of the even-AA polonium isotopes 192210,216,218^{192-210,216,218}Po has been performed using the 6p37s6p^37s 5S2^5S_2 to 6p37p6p^37p 5P2^5P_2 (λ=843.38\lambda=843.38 nm) transition in the polonium atom (Po-I) at the CERN ISOLDE facility. The comparison of the measured isotope shifts in 200210^{200-210}Po with a previous data set allows to test for the first time recent large-scale atomic calculations that are essential to extract the changes in the mean-square charge radius of the atomic nucleus. When going to lighter masses, a surprisingly large and early departure from sphericity is observed, which is only partly reproduced by Beyond Mean Field calculations.Comment: As submitted to PR

    Coulomb excitation of 73Ga

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    The B(E2; Ii -> If) values for transitions in 71Ga and 73Ga were deduced from a Coulomb excitation experiment at the safe energy of 2.95 MeV/nucleon using post-accelerated beams of 71,73Ga at the REX-ISOLDE on-line isotope mass separator facility. The emitted gamma rays were detected by the MINIBALL-detector array and B(E2; Ii->If) values were obtained from the yields normalized to the known strength of the 2+ -> 0+ transition in the 120Sn target. The comparison of these new results with the data of less neutron-rich gallium isotopes shows a shift of the E2 collectivity towards lower excitation energy when adding neutrons beyond N = 40. This supports conclusions from previous studies of the gallium isotopes which indicated a structural change in this isotopical chain between N = 40 and N = 42. Combined with recent measurements from collinear laser spectroscopy showing a 1/2- spin and parity for the ground state, the extracted results revealed evidence for a 1/2-; 3/2- doublet near the ground state in 73 31Ga42 differing by at most 0.8 keV in energy
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