257 research outputs found
β-Decay Half-Lives of 110 Neutron-Rich Nuclei across the N=82 Shell Gap: Implications for the Mechanism and Universality of the Astrophysical r Process
No full textInternational audienceThe β-decay half-lives of 110 neutron-rich isotopes of the elements from Rb37 to Sn50 were measured at the Radioactive Isotope Beam Factory. The 40 new half-lives follow robust systematics and highlight the persistence of shell effects. The new data have direct implications for r-process calculations and reinforce the notion that the second (A≈130) and the rare-earth-element (A≈160) abundance peaks may result from the freeze-out of an (n,γ)⇄(γ,n) equilibrium. In such an equilibrium, the new half-lives are important factors determining the abundance of rare-earth elements, and allow for a more reliable discussion of the r process universality. It is anticipated that universality may not extend to the elements Sn, Sb, I, and Cs, making the detection of these elements in metal-poor stars of the utmost importance to determine the exact conditions of individual r-process events
Approaching the precursor nuclei of the third r-process peak with RIBs
No full textThe rapid neutron nucleosynthesis process involves an enormous amount of very exotic neutron-rich nuclei, which represent a theoretical and experimental challenge. Two of the main decay properties that affect the final abundance distribution the most are half-lives and neutron branching ratios. Using fragmentation of a primary 238U beam at GSI we were able to measure such properties for several neutron-rich nuclei from 208Hg to 218Pb. This contribution provides a short update on the status of the data analysis of this experiment, together with a compilation of the latest results published in this mass region, both experimental and theoretical. The impact of the uncertainties connected with the beta-decay rates and with beta-delayed neutron emission is illustrated on the basis of r-process network calculations. In order to obtain a reasonable reproduction of the third r-process peak, it is expected that both half-lives and neutron branching ratios are substantially smaller, than those based on FRDM+QRPA, commonly used in r-process model calculations. Further measurements around N ∼ 126 are required for a reliable modelling of the underlying nuclear structure, and for performing more realistic r-process abundance calculations.</p
Magnetic moment measurements in A ~ 140 Te, Xe, Ba and Ce isotopes using the Transient Field technique
No full textThe new neutron depth profiling instrument N4DP at the Heinz Maier-Leibnitz Zentrum
No full textThe cold neutron guide of the Prompt Gamma Activation Analysis (PGAA) instrument (Revay et al. 2015) at the Heinz Maier-Leibnitz Zentrum (MLZ) provides an excellent opportunity for neutron depth profiling (NDP) due to its high collimated neutron flux. We present the concept, layout and first measurements with the new N4DP facility set-up at this beamline. A special focus is put on background analysis and instrument characterization. We present measurements of a NIST reference sample and of boron-containing float glasses which are used for neutron optical waveguides. We give an outlook concerning the ongoing development of position-resolved NDP using silicon microstrip detectors
Shape coexistence in the light francium isotopes: First implementation of alpha-tagged Coulomb excitation
No full textCERN-INTC-2010-076 ; INTC-P-28
Shape coexistence in the light francium isotopes: First implementation of alpha-tagged Coulomb excitation
No full textCERN-INTC-2010-076 ; INTC-P-28
Shape coexistence in the light francium isotopes: First implementation of alpha-tagged Coulomb excitation
No full textCERN-INTC-2010-076 ; INTC-P-28
Materials science applications of Neutron Depth Profiling at the PGAA facility of Heinz Maier-Leibnitz Zentrum
No full textNeutron depth profiling (NDP) is a non-destructive, isotope-sensitive profiling technique to monitor concentration profiles in almost any material matrix. Since NDP is sensitive to 6Li and lithium is widely used for different material science applications such as ceramics, optical waveguides or energy-storage systems, NDP offers answers to a broad spectrum of research questions. In the present work, the recently developed instrument N4DP at MLZ is used to address two research questions which are hardly accessible by conventional analytical techniques. First, the homogeneity of lithium formations within lithium niobate thin films for optical waveguide applications is investigated. Afterwards, the accumulation of inactive lithium in the solid-electrolyte-interphase (SEI) of silicon-graphite electrodes for lithium-ion batteries is studied ex situ. Since the material mass loading differs considerably between the two applications, a new analytical technique is introduced which mathematically separates the different particle signals and thus allows to investigate samples with high mass loadings
Nuclear astrophysics with radioactive ions at FAIR
No full textThe nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process beta-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes
Nuclear structure of Si-37,Si-38 investigated by decay spectroscopy of Al-37,Al-38
No full textWe present a study on the beta decays of the neutron-rich isotopes Al-37 and Al-38, produced by projectile fragmentation of a Ca-48 beam with an energy E - 345 A MeV at the RIKEN Nishina Center. The half-lives of Al-37 and Al-38 have been measured to 11.5(4) ms and 9.0(7) ms, respectively, using the CAITEN implantation and decay detector setup. The level schemes for Si-37 and Si-38 were deduced by employing gamma-gamma coincidence spectroscopy following the event-by-event identification of the implanted nuclei. Comparison to large scale nuclear shell model calculations allowed for a tentative assignment of spin and parity of the populated states. The data indicate that the classical shell gap at magic neutron number N = 28 between the nu f(7/2) and nu p(3/2) orbits gets reduced by 0.3 MeV in this region leading to low-energy states with intruder configuration in Si-37.BMBF [06MT9156, 05P12WOFNF]; DFG (Cluster of Excellence: "Origin and Structure of the Universe") [KR2326/2-1]; KAKENHI [19340074, 25247045]; RIKEN President's FundSCI(E)[email protected]
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