H. Weick

Observation of non-exponential orbital electron capture decays of hydrogen-like 140Pr and 142Pm ions

Abstract We report on time-modulated two-body weak decays observed in the orbital electron capture of hydrogen-like 140 Pr 59+ and 142 Pm 60+ ions coasting in an ion storage ring. Using non-destructive single ion, time-resolved Schottky mass spectrometry we found that the expected exponential decay is modulated in time with a modulation period of about 7 seconds for both systems. Tentatively this observation is attributed to the coherent superposition of finite mass eigenstates of the electron neutrinos from the weak decay into a two-body final state.

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.

Experimental studies of heavy-ion slowing down in matter

Measurements of heavy-ion slowing down in matter differ in many aspects from experiments with light particles like protons and α-particles. An overview of the special experimental requirements, methods, data analysis and interpretation is presented for heavy-ion stopping powers, energy- and angular-straggling and ranges in the energy domain from keV/u up to GeV/u. Characteristic experimental results are presented and compared with theory and semiempirical predictions. New applications are outlined, which represent a challenge to continuously improve the knowledge of heavy-ion slowing down.

Superallowed Gamow-Teller decay of the doubly magic nucleus 100Sn

The shell structure of atomic nuclei is associated with ‘magic numbers’ and originates in the nearly independent motion of neutrons and protons in a mean potential generated by all nucleons. During β+-decay, a proton transforms into a neutron in a previously not fully occupied orbital, emitting a positron–neutrino pair with either parallel or antiparallel spins, in a Gamow–Teller or Fermi transition, respectively. The transition probability, or strength, of a Gamow–Teller transition depends sensitively on the underlying shell structure and is usually distributed among many states in the neighbouring nucleus. Here we report measurements of the half-life and decay energy for the decay of 100Sn, the heaviest doubly magic nucleus with equal numbers of protons and neutrons. In the β-decay of 100Sn, a large fraction of the strength is observable because of the large decay energy. We determine the largest Gamow–Teller strength so far measured in allowed nuclear β-decay, establishing the ‘superallowed’ nature of this Gamow–Teller transition. The large strength and the low-energy states in the daughter nucleus, 100In, are well reproduced by modern, large-scale shell model calculations.

High-resolution measurement of the time-modulated orbital electron capture and of the β+ decay of hydrogen-like 142Pm60+ ions

Abstract The periodic time modulations, found recently in the two-body orbital electron capture (EC) decay of both, hydrogen-like 140Pr58+ and 142Pm60+ ions, with periods near to 7 s and amplitudes of about 20%, were re-investigated for the case of 142Pm60+ by using a 245 MHz resonator cavity with a much improved sensitivity and time resolution. We observed that the exponential EC decay is modulated with a period T = 7.11 ( 11 ) s , in accordance with a modulation period T = 7.12 ( 11 ) s as obtained from simultaneous observations with a capacitive pick-up, employed also in the previous experiments. The modulation amplitudes amount to a R = 0.107 ( 24 ) and a P = 0.134 ( 27 ) for the 245 MHz resonator and the capacitive pick-up, respectively. These new results corroborate for both detectors exactly our previous findings of modulation periods near to 7 s , though with distinctly smaller amplitudes. Also the three-body β + decays have been analyzed. For a supposed modulation period near to 7 s we found an amplitude a = 0.027 ( 27 ) , compatible with a = 0 and in agreement with the preliminary result a = 0.030 ( 30 ) of our previous experiment. These observations could point at weak interaction as origin of the observed 7 s -modulation of the EC decay. Furthermore, the data suggest that interference terms occur in the two-body EC decay, although the neutrinos are not directly observed.

Energy and range focusing of in-flight separated exotic nuclei - A study for the energy-buncher stage of the low-energy branch of the Super-FRS

Abstract The relative momentum spread of in-flight separated exotic nuclear beams produced in fragmentation and/or fission reactions is of the order of a few percent. A new technique is presented, which reduces the momentum spread significantly, and first experimental results obtained with relativistic projectile fragments are shown. This technique is the key to experiments with slowed-down and stopped beams, in particular for the efficient stopping of relativistic exotic nuclei in gas-filled stopping cells. It will be employed at the energy-buncher stage of the low-energy branch of the Super-FRS facility. The ion-optical design of the energy buncher is presented and a brief outlook to the experimental program is given.

First experimental results of a cryogenic stopping cell with short-lived, heavy uranium fragments produced at 1000 MeV/u

A cryogenic stopping cell (CSC) has been commissioned with U-238 projectile fragments produced at 1000 MeV/u. The spatial isotopic separation in flight was performed with the FRS applying a monoenergetic degrader. For the first time, a stopping cell was operated with exotic nuclei at cryogenic temperatures (70 to 100K). A helium stopping gas density of up to 0.05mg/cm(3) was used, about two times higher than reached before for a stopping cell with RF ion repelling structures. An overall efficiency of up to 15%, a combined ion survival and extraction efficiency of about 50%, and extraction times of 24ms were achieved for heavy a-decaying uranium fragments. Mass spectrometry with a multiple-reflection time-of-flight mass spectrometer has demonstrated the excellent cleanliness of the CSC. This setup has opened a new field for the spectroscopy of short-lived nuclei. Copyright (C) EPLA, 2013

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.

Proton-proton correlations observed in two-proton decay of 19Mg and 16Ne

Proton-proton correlations were observed for the two-proton decays of the ground states of 19 Mg and 16 Ne. The trajectories of the respective decay products, 17 Ne + p + p and 14 O + p + p, were measured by using a tracking technique with microstrip detectors. These data were used to reconstruct the angular correlations of fragments projected on planes transverse to the precursor momenta. The measured three-particle correlations reflect a genuine three-body decay mechanism and allowed us to obtain spectroscopic information on the precursors with valence protons in the sd shell.