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News Archive 2010

18.12.10: Recent nuclear structure study results published

Recent nuclear structure study results just appeared in three Phys. Rev. C articles:

R. B. Cakirli et al. report on the indication of a mini-valence Wigner-like energy in heavy nuclei. Using double differences of binding energies, known as δVpn(Z,N) values, a similar effect as Wigner's spin-isospin symmetry seen in light nuclei previously is obtained in heavy nuclei.

Please read more in the article ... >

R. B. Cakirli et al. report on correlations of experimental isotope shifts with spectroscopic and mass observables. It has been shown that there are remarkable correlations among a number of differential observables in even-even nuclei spanning large regions of the nuclear chart and very different physical properties of nuclei ranging from single particle binding to nuclear sizes and collective properties of the many-body system itself.

Please read more in the article ... >

P. Vingerhoets et al. report on measurements of the ground-state nuclear spins and magnetic and quadrupole moments of the copper isotopes from 61Cu up to 75Cu. The experiments were performed at the CERN On-Line Isotope Mass Separator ISOLDE external Link facility, using the technique of collinear laser spectroscopy. The experimental results have been compared to large-scale shell-model calculations.

Please read more in the article ... >

17.12.10: Review article: Beta decay of highly charged ions

In a recently in "Reports on Progress in Physics" published review article Yuri A. Litvinov and Fritz Bosch present and discuss studies of two-body beta decays, namely bound-state beta decay and orbital electron capture at the heavy-ion complex GSI external Link in Darmstadt. There, the fragment separator facility FRS external Link allows the production and separation of exotic, highly charged nuclides, which can then be stored and investigated in the storage ring facility ESR external Link.

Beta decay of highly charged ions has attracted much attention in recent years since stellar nucleosynthesis proceeds at high temperatures where the involved atoms are highly ionized. Furthermore, one-electron ions are ideal well-defined quantum-mechanical systems for studying beta decays. Beta decays of highly charged ions show the largest modifications of nuclear half-lives with respect to neutral atoms.

In their review Yuri A. Litvinov and Fritz Bosch describe in detail the production and separation of highly charged radionuclides, the storage ring radioactive beam facilities and the beta decay of stored highly charged exotic nuclei. They also address challenging but not yet performed experiments and give prospects for the new radioactive beam facilities, such as FAIR in Darmstadt external Link, IMP in Lanzhou external Link and RIKEN in Wako external Link.

Please read more in the article ... >
11.11.10: Discovery of a long-lived low-lying isomeric state in 80Ga

In a just in Phys. Rev. C published article B. Cheal et al. report the results of collinear laser spectroscopy measurements on the 80Ga isotope at ISOLDE external Link, CERN, Geneva.
The hyperfine structures of two nuclear states were measured in 80Ga, discovering a low-lying isomeric state with a half-life much greater than 200 ms. One of the structures is assigned nuclear spin I=3 from model-independent analysis of the data alone. Shell-model calculations suggest that the other state is nuclear spin I=6 and that it is the ground state.

Further Penning trap mass measurements and complementary studies will allow to determine experimentally which of the two states is the isomeric state and to measure properties such as the excitation energy and half-life.

Please read more in the PRC article ... >
21.10.10: Discovery of Highly Excited Long-Lived Isomers through Direct Mass Measurements

In a recently in Phys. Rev. Lett. published article M. W. Reed et al. report on the study of cooled 197Au projectile-fragmentation products, which has been performed with the Experimental Storage Ring external Link (ESR) at GSI, Darmstadt, Germany.

There is a long-standing prediction of an isomer-rich landscape for deformed neutron-rich Z ~ 72 (hafnium) nuclides, which has been supported by detailed model calculations. Major developments in storage-ring techniques mean that the mass of an individual ion can now be measured with sufficient accuracy to differentiate between a nuclear ground state and a metastable excited state, known as an isomer.

In the experiment projectilelike fragments have been injected into the ESR and their mass has been measured. In this way, new long-lived hafnium and tantalum isomers (183,184,186Hf and 186,187Ta) have been discovered. This results support the prediction of a strongly favored isomer region near neutron number 116.

Please read more in the PRL article, which is among the "Suggestions" of the editors of Physical Review Letters ... >

Please see also the related press releases.

01.10.10: A new route to the neutrino mass determination?

The absolute mass of the neutrino is of fundamental importance for physics and cosmology. The study of nuclear electron capture (EC) offers an exciting alternative to β-decay experiments for the determination of the neutrino mass. The progress in Penning trap mass spectrometry and cryogenic micro-calorimetry enables now a neutrino mass determination at a considerably increased level of accuracy.

In a just in Physics Letters B published article S. Eliseev et al. report on the determination of the QEC-value of the electron capture in 194Hg by direct mass measurements of 194Hg and 194Au at the ISOLTRAP external Link Penning trap mass spectrometer at ISOLDE/CERN external Link.

The resulting new QEC-value of 194Hg is 29(4) keV. Since the binding energy of the K-shell electron exceeds the QEC-value, nuclear capture of the K electron can now be excluded, while it would have been allowed by the previous AME2003 evaluated value (and uncertainty) of QEC = 69(14) keV.

The upper limit for the neutrino mass is presently 225 eV. 20 eV would probably be a limit of a determination of an upper limit for the electron neutrino mass from EC in 194Hg for the next few years. Considerable improvement of this technique could further lower this value.

Please read more in the article ... >
FAIR STI approved the MATS and LaSpec Technical Design Report
Technical Design Report published as "Special Issue"

On May 7th 2010, the FAIR STI (working group on Scientific and Technical Issues) approved the MATS and LaSpec Technical Design Report. The MATS and LaSpec facilities will be built at the Low Energy Branch of the Superconducting Fragment Separator of FAIR, to perform high-precision experiments on very exotic isotopes using lasers and ion traps.

The Technical Design report was adapted for publication in a special volume of the European Physical Journal Special Topics external Link, edited by Daniel Rodríguez (Universidad de Granada), Klaus Blaum (Max-Planck-Institut für Kernphysik Heidelberg) and Wilfried Nörtershäuser (Johannes Gutenberg-Universität Mainz). The paper is signed by 104 scientists from 30 institutes in Germany, Finland, Russia, Spain, France, Great Britain, Sweden, India, Switzerland, Belgium, United States, and Canada forming the MATS and LASPEC collaborations.

Please read more in the article ... >
17.07.10: First mass determination of 96,97Kr by Penning-trap mass spectrometry

In a just in Phys. Rev. Lett. published article S. Naimi et al. report on the first mass measurements of 96,97Kr using the ISOLTRAP external Link Penning-trap spectrometer at ISOLDE external Link, CERN, Geneva.

These new measurements extend the mass surface beyond N = 60 for Z = 36 and yield results, which show behavior in sharp contrast to the heavier neighbors where a sudden and intense deformation is present. Thus the masses of 96,97Kr establish the limit of the region of strong deformation and allow, for the first time, mapping the lower boundary of the region of critical-point behavior.

This discovery of one of the most remarkable examples of nuclear shape transition spawned extensive experimental and theoretical exploration. It also illustrates how powerful Penning-trap mass spectrometry can be by providing key structural information.

Please read more in the article ... >

Please see also the published press releases.

26.06.10: CAS Visiting Professorship awarded to Prof. Yuri A. Litvinov
certificate award ceremony

We congratulate our division member Yuri for this high scientific honor!
The certificate award ceremony of CAS Visiting Professorships for Senior International Scientists was held at the Institute of Modern Physics (IMP), Chinese Academy of Sciences on 18.06.2010.

Please read more about the award ceremony on the CAS website ... >

24.06.10: Precision measurements of nuclear spins and moments of neutron-rich Ga isotopes

In a recently in Phys. Rev. Lett. published article B. Cheal et al. report on precision measurements using collinear laser spectroscopy on Ga (Z = 31) isotopes at ISOLDE external Link, CERN. A gas-filled linear Paul trap (ISCOOL) was used to extend the measurements towards very neutron-rich Ga isotopes (N = 36-50).

The nuclear spins, magnetic dipole, and electric quadrupole moments have been measured for the odd-A Ga isotopes in the range A = 67-81. The anomalous ground state spins of 73Ga (I = 1/2) and 81Ga (I = 5/2), as well as the sign change in the quadrupole moments of 75,77,79Ga, suggest a changing shell structure of Ga from N = 42 onwards.

Please read more in the article ... >
17.06.10: First direct mass measurements of transuranium elements

In a current Phys. Rev. C article M. Dworschak et al. report on accurate mass measurements on the three nobelium isotopes 252–254No. The measurements were performed at the Penning trap mass spectrometer SHIPTRAP external Link at GSI Darmstadt. These first direct mass measurements on transuranium elements resulted in unambiguous ground-state mass values independent from the knowledge of any nuclear level scheme.

The SHIPTRAP results confirm the previously determined masses for all three nobelium isotopes and demonstrate that the α-decay schemes were all correct. In addition, most of the AME 2003 external Link mass values determined from decay energies have been slightly improved. The area of nuclides with well-known mass values has been extended for the first time to the region of transuranium elements and thus moved a step closer to the expected island of stability. It is planned to extend direct mass measurements with SHIPTRAP to higher Z nuclides.

Please read more in the article ... >
18.05.10: A cryogenic electrostatic trap for long-time storage of keV ion beams

In a just in Review of Scientific Instruments published article M. Lange et al. report on the realization and operation of a fast ion beam trap of the linear electrostatic type employing liquid helium cooling to reach extremely low blackbody radiation temperature and residual gas density and, hence, long storage times of more than 5 min which are unprecedented for keV ion beams.

Inside a beam pipe that can be cooled to temperatures <15 K, with 1.8 K reached in some locations, an ion beam pulse can be stored at kinetic energies of 2-20 keV between two electrostatic mirrors. Along with an overview of the cryogenic trap design, a measurement of the residual gas density inside the trap is presented in the article resulting in only 2·103 cm-3, which for a room temperature environment corresponds to a pressure in the 10-14 mbar range.

The device, called the cryogenic trap for fast ion beams (CTF) external Link, is now being used to investigate molecules and clusters at low temperatures, but has also served as a design prototype for the cryogenic heavy-ion storage ring currently under construction at the Max-Planck Institute for Nuclear Physics.

Please read more in the article ... >
10.05.10: Accuracy studies at the Penning trap mass spectrometer TRIGA-TRAP

In a just in Eur. Phys. J. D published article J. Ketelaer et al. report about accuracy studies at TRIGA-TRAP. TRIGA-TRAP is a double-Penning trap mass spectrometer for short-lived nuclides installed at the Research Reactor TRIGA Mainz external Link as part of the TRIGA-SPEC project.

Masses are needed in many fields of physics with different requirements on the accuracy. The highest precision can be achieved by converting the mass measurement into a frequency measurement. At TRIGA-TRAP the ion mass is determined via a measurement of the cyclotron frequency of the stored ion by the time-of-flight ion-cyclotron-resonance (TOF-ICR) detection technique. In order to determine the magnetic field inside the trap carbon cluster ions are used as ideal reference ions. At TRIGA-TRAP extensive cross-reference measurements of well-known frequency ratios using various sizes of carbon cluster ions 12Cn+ (10<=n<=23) were performed to determine the sources of uncertainty for mass measurements. Fluctuations of the magnetic field cause an uncertainty in the frequency ratio and a mass-dependent systematic shift of the frequency ratio has been found as well.

In the first mass measurement at TRIGA-TRAP the frequency ratio between the reference ion 12C16+ and 197Au+ has been determined. Since the mass uncertainty of 197Au is only 0.6 keV this isotope can be used to verify the accuracy of measured masses besides carbon cluster ions.

Please read more in the article ... >
14.04.10: Featured IOP article: Isotope shift measurements in the 2s1/2 -> 2p3/2 transition of Be+

In a recently in the Journal of Physics G published featured article external Link (i.e. an article of high-interest across IOP content) M. Žáková et al. report about isotope shift measurements in the 2s1/2 -> 2p3/2 transition of Be+ ions with an accuracy of 2 MHz.

The measurements were performed at the on-line isotope separator (ISOLDE) at CERN using advanced collinear laser spectroscopy with two counterpropagating laser beams. From the isotope shifts between 9Be and 7,10,11Be, high-accuracy mass shift calculations and the charge radius of the reference isotope 9Be the nuclear charge radii for the isotopes 7,10Be and the one-neutron halo nucleus 11Be were determined. The found decreasing charge radii from 7Be to 10Be are explained by the cluster structure of the nuclei. The increase from 10Be to 11Be is mainly caused by the center-of-mass motion of the 10Be core caused by the halo neutron.

Please read more in the featured article ... >
04.03.10: Klaus Blaum receives GENCO Membership Award 2010

Division director Klaus Blaum has been selected to receive the GENCO Membership Award 2010 for his outstanding scientific work. The GENCO Award session takes place on March 4th, 2010 during the NUSTAR Annual Meeting 2010.

Main goal of the GSI Exotic Nuclei Community (GENCO) is to reward young scientists for outstanding research in nuclear physics, nuclear astrophysics and closely related fields. Besides the award for young scientists, each year also senior scientists are elected for the GENCO membership. President of the GSI Exotic Nuclei Community is Prof. G. Münzenberg (GSI). Please visit the GENCO website external Link for more information.

23.02.10: Review article about the importance of Penning trap experiments for fundamental physics

In a recently in Contemporary Physics published review article Klaus Blaum, Yuri Novikov and Günter Werth demonstrate the impact of Penning trap mass spectrometry on fundamental problems in modern physics.

Initially, the basic aspects of accurate Penning trap mass measurements are addressed. The necessary three-dimensional electromagnetic confinement of particles in a Penning trap is realized by a superposition of a strong homogeneous magnetic field and a weak electrostatic quadrupole field. To reduce the effects of the imperfections in the trapping fields the trapped particles are cooled inside the trap. The different applied cooling methods e.g. buffer gas cooling and laser cooling are discussed in the article as well as the particle manipulation in the trap.

Mass determination in a Penning trap relies on the fact that the ratio of cyclotron frequencies of two particles with the same charge state in the same magnetic field is equal to the ratio of their masses. The main cyclotron frequency measurement techniques i.e. the destructive time-of-flight method and nondestructive Fourier Transform Ion Cyclotron Resonance method are described.

The Penning trap methods and technology have been continuously improved to increase measurement accuracy and develop new application areas. The required accuracy of mass measurements ranges from 10-6 for particle identification (e.g. separation of isobars) to below 10-11 for fundamental physical questions (e.g. separation of atomic states).

Modern Penning traps are applied to test the Standard Model (i.e. quantum chromodynamics QCD and electroweak theory) in the low energy region. Especially the precise determination of fundamental constants like the fine-structure constant α provides important information. It is intended to increase the measurement precision in order to investigate the time dependence of fundamental constants. Further, accurate atomic masses from Penning trap measurements yield information on the postulated unitarity of the CKM quark-mixing matrix.

Penning trap spectrometry allows the test of quantum-electrodynamics (QEQ) e.g. by measuring the free electron g-factor and the bound electron g-factor. The accurate measurement of the electron–positron g-factor difference and the proton–antiproton mass difference yields a test of the CPT-invariance theorem and has confirmed CPT-conservation until now.

Precise mass measurements provide a test of Einstein’s energy/mass relation E = mc2 as well as precise atomic mass differences for neutrino mass determination.

In order to investigate even radioactive nuclides in Penning traps, they are installed on-line to the facility which produces these charged particles. The article explains the important on-line Penning traps at ISOL (e.g. ISOLTRAP external Link at ISOLDE, CERN, Geneva) resp. in-flight facilities (e.g. SHIPTRAP external Link at UNILAC, GSI/Darmstadt, Germany).

Penning traps are also widely used in exploration of nuclear physics and nuclear astrophysics phenomena e.g. for mass mapping of exotic nuclides which are far off stability.

Please read more in the review article ... >
11.02.10: "Nature" article about first direct mass measurements of transuranium nuclides published

Members of our division participated in the first direct mass measurements of the nobelium isotopes 252–254No within an international collaboration under the leadership of GSI Helmholtzzentrum für Schwerionenforschung external Link in Darmstadt, Germany. The results of this first foray into the region of transuranium elements have just been published in the prestigious scientific journal "Nature" external Link.

Superheavy elements above the heaviest natural element uranium can be produced and observed in the lab. All these known transuranium nuclides are unstable, but competing theoretical models predict the existence of even heavier elements, that are stable though. This region in the chart of nuclides is called the "island of stability". If this island would be found, the physicists would especially learn more about the creation of heavy elements up to uranium by stellar nucleosynthesis.

Due to Einstein's mass–energy equivalence accurate mass measurements allow the precise determination of the nuclear binding energy, which is crucial for the nuclear stability. Thus this measurements provide important tests for competing theoretical models and their different predictions for the position of the island of stability.

Our knowledge of the binding energy of superheavy nuclides has been based only on the detection of their decay products so far. This indirect method introduces considerable uncertainties and direct high-precision mass measurements using Penning traps provide an improvement in accuracy up to a factor of ten. Recently, the first high-precision mass measurements of the nobelium isotopes 252–254No were performed with the double Penning-trap mass spectrometer SHIPTRAP external Link at GSI. A destructive time-of-flight method was used to measure the cyclotron frequency of the ions from which the ion mass was determined.

The SHIPTRAP mass values for 252–254No agree within their uncertainties with the AME2003 data external Link, which were deduced from spectroscopy data of No-decays. This confirmed nobelium masses serve as accurate reference points in the mass region between uranium and the predicted island of stability. Unlike the indirect decay-based methods, the new direct mass measurement method will also be applicable to very long-lived superheavy elements and thus allow to detect nuclides of the island of stability.

It is planned to extend the accurate direct mass determinations at SHIPTRAP to the transactinide region. Furthermore it is intended to enhance the used ion detection by applying the non-destructive Fourier Transform-Ion Cyclotron Resonance (FT-ICR) detection method. This will allow for mass measurements of single superheavy nuclides with production rates in the range below one ion per hour.

Please read more in the "Nature" article external Link, the MPG news external Link and the press releases about the successful accurate mass measurements of superheavy nuclides.