R. Knöbel

Measurement of the {beta}{sup +} and Orbital Electron-Capture Decay Rates in Fully Ionized, Hydrogenlike, and Heliumlike {sup 140}Pr Ions

We report on the first measurement of the beta+ and orbital electron-capture decay rates of 140Pr nuclei with the simplest electron configurations: bare nuclei, hydrogenlike, and heliumlike ions. The measured electron-capture decay constant of hydrogenlike 140Pr58+ ions is about 50% larger than that of heliumlike 140Pr57+ ions. Moreover, 140Pr ions with one bound electron decay faster than neutral 140Pr0+ atoms with 59 electrons. To explain this peculiar observation one has to take into account the conservation of the total angular momentum, since only particular spin orientations of the nucleus and of the captured electron can contribute to the allowed decay.

Exploring the anomaly in the interaction cross section and matter radius of 23O

New measurements of the interaction cross sections of 22,23O at 900A MeV performed at the GSI, Darmstadt are reported that address the unsolved puzzle of the large cross section previously observed for 23O. 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 22O+neutron description of 23O as well.

Schottky mass measurements of heavy neutron-rich nuclides in the element range 70 <= Z <= 79 at the GSI Experimental Storage Ring

D. Shubina, 2, 3 R.B. Cakirli, 4 Yu.A. Litvinov, 3 K. Blaum, C. Brandau, 5 F. Bosch, J.J. Carroll, R.F. Casten, D.M. Cullen, I.J. Cullen, A.Y. Deo, B. Detwiler, C. Dimopoulou, F. Farinon, H. Geissel, 11 E. Haettner, M. Heil, R.S. Kempley, C. Kozhuharov, R. Knobel, J. Kurcewicz, N. Kuzminchuk, S.A. Litvinov, Z. Liu, R. Mao, C. Nociforo, F. Nolden, Z. Patyk, W.R. Plass, A. Prochazka, M.W. Reed, 15 M.S. Sanjari, 16 C. Scheidenberger, 11 M. Steck, Th. Stohlker, 17, 18 B. Sun, 19 T.P.D. Swan, G. Trees, P.M. Walker, 20 H. Weick, N. Winckler, 3 M. Winkler, P.J. Woods, T. Yamaguchi, and C. Zhou Max-Planck-Institut fur Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany Fakultat fur Physik und Astronomie, Universitat Heidelberg, Philosophenweg 12, 69120 Heidelberg, Germany GSI Helmholtzzentrum fur Schwerionenforschung, Planckstrase 1, 64291 Darmstadt, Germany Department of Physics, University of Istanbul, Istanbul, Turkey ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum fur Schwerionenforschung, 64291 Darmstadt, Germany US Army Research Laboratory, 2800 Powder Mill Road, Adelphi MD, USA Wright Nuclear Structure Laboratory, Yale University, New Haven, Connecticut 06520, USA Schuster Laboratory, University of Manchester, Manchester M13 9PL, United Kingdom Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom Youngstown State University, One University Plaza, Youngstown, Ohio 44555, USA II Physikalisches Institut, Justus-Liebig-Universitat Giesen, 35392 Giesen, Germany School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, People’s Republic of China National Centre for Nuclear Research, PL-00681 Warsaw, Poland Department of Nuclear Physics, R.S.P.E., Australian National University, Canberra ACT 0200, Australia Goethe-Universitat Frankfurt, 60438 Frankfurt, Germany Friedrich-Schiller-Universitat Jena, 07737 Jena, Germany Helmholtz-Institut Jena, 07743 Jena, Germany School of Physics and Nuclear Energy Engineering, Beihang University, 100191 Beijing, PRC CERN, CH-1211 Geneva 23, Switzerland Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan Storage-ring mass spectrometry was applied to neutron-rich Au projectile fragments. Masses of Lu, Hf, Ta, W, and Re nuclei were measured for the first time. The uncertainty of previously known masses of W and Os nuclei was improved. Observed irregularities on the smooth two-neutron separation energies for Hf and W isotopes are linked to the collectivity phenomena in the corresponding nuclei.

First Measurement of Several β-Delayed Neutron Emitting Isotopes Beyond N=126

The β-delayed neutron emission probabilities of neutron rich Hg and Tl nuclei have been measured together with β-decay half-lives for 20 isotopes of Au, Hg, Tl, Pb, and Bi in the mass region N≳126. These are the heaviest species where neutron emission has been observed so far. These measurements provide key information to evaluate the performance of nuclear microscopic and phenomenological models in reproducing the high-energy part of the β-decay strength distribution. This provides important constraints on global theoretical models currently used in r-process nucleosynthesis.

Measurements of α-decay half-lives at GSI

One of the major problems in nuclear astrophysics concerns the estimation of electron screening effects on nuclear reaction rates. We have proposed investigating the electron screening effects of nuclear systems which decay via α-particles, using fragmented beams at relativistic energies produced at the present GSI FRS-ESR facility. By looking at the modification of the half-lives and Qα-value of highly charged emitters, we expect to estimate the electron screening energies.

Technique for Resolving Low-lying Isomers in the Experimental Storage Ring (ESR) and the Occurrence of an Isomeric State in 192Re

A recent experiment using projectile fragmentation of a 197Au beam on a 9Be target, combined with the fragment recoil separator and experimental storage ring at ring at GSI, has uncovered an isomeric state in 192Re at 267(10) keV with a half-life of ~60 s. The data analysis technique used to resolve the isomeric state from the ground state is discussed.

Direct observation of long-lived isomers in Bi212

Long-lived isomers in (212)Bi have been studied following (238)U projectile fragmentation at 670 MeV per nucleon. The fragmentation products were injected as highly charged ions into a storage ring, giving access to masses and half-lives. While the excitation energy of the first isomer of (212)Bi was confirmed, the second isomer was observed at 1478(30) keV, in contrast to the previously accepted value of >1910 keV. It was also found to have an extended Lorentz-corrected in-ring half-life >30 min, compared to 7.0(3) min for the neutral atom. Both the energy and half-life differences can be understood as being due a substantial, though previously unrecognized, internal decay branch for neutral atoms. Earlier shell-model calculations are now found to give good agreement with the isomer excitation energy. Furthermore, these and new calculations predict the existence of states at slightly higher energy that could facilitate isomer deexcitation studies.

β-delayed three-proton decay ofAr31

The beta decay of 31Ar, produced by fragmentation of a 36Ar beam at 880 MeV/nucleon, was investigated. Identified ions of 31Ar were stopped in a gaseous time projection chamber with optical readout allowing to record decay events with emission of protons. In addition to \b{eta}-delayed emission of one and two protons we have clearly observed the beta-delayed three-proton branch. The branching ratio for this channel in 31Ar is found to be 0.07(2)%.

Electron Screening Effects on a-decay

An open problem in Nuclear Astrophysics concerns the understanding of electron‐screening effects on nuclear reaction rates at stellar energies. In this framework, we have proposed to investigate the influence of the electron cloud on α‐decay by measuring Q‐values and α‐decay half‐lives of fully stripped, H‐like and He‐like ions. These kinds of measurements have been feasible just recently for highly‐charged radioactive nuclides by fragmentation of 238U at relativistic energies at the FRS‐ESR facility at GSI. In this way it is possible to produce, efficiently separate and store highly‐charged α‐emitters. Candidates for the proposed investigation were carefully selected and will be studied by using the Schottky Mass Spectroscopy technique. In order to establish a solid reference data set, lifetimes and Qα‐value measurements of the corresponding neutrals have been performed directly at the FRS, by implanting the separated ions into an active Silicon stopper.

Approaching the precursor nuclei of the third r-process peak with RIBs

The 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 eta-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.