Towards direct mass measurements of nobelium at SHIPTRAP

The Penning-trap mass spectrometer SHIPTRAP allows precision mass measurements of rare isotopes produced in fusion-evaporation reactions. In the first period of operation the masses of more than 50 neutron-deficient radionuclides have been measured. In this paper the perspectives for direct mass measurements of rare isotopes around nobelium are discussed and the achievable precision is addressed. The temporal stability of the magnetic field, an important issue for the long measurement times resulting from the low production rates, was investigated and the time-dependent uncertainty due to magnetic field fluctuations was determined. Based on the present performance direct mass measurements of nobelium isotopes are already feasible. With several technical improvements heavier elements between Z=102–105 will be in reach.     

Carbon-cluster mass calibration at SHIPTRAP

A carbon-cluster ion source has been installed and tested at SHIPTRAP, the Penning-trap mass spectrometer for precision mass measurements of heavy elements at GSI. Carbon-cluster ions ¹²C_n ⁺, 5 ≤n ≤23, were produced by laser-induced desorption and ionization from a carbon sample. They were tested for the first time as reference ions in an on-line mass measurement of the radionuclides ¹⁴⁴Dy, ¹⁴⁶Dy and ¹⁴⁷Ho. In addition, carbon clusters of various sizes were used for an investigation of the systematic uncertainty of SHIPTRAP covering a mass range from 84 u to 240 u. The mass-dependent uncertainty was found to be negligible for the case of (m-m _ref)< 100 u. However, a systematic uncertainty of 4.5 ×10^-8 was revealed.     

Precision mass measurements of 40Ca17+ and 40Ca19+ ions in a Penning trap

High-precision mass measurements on lithium-like and hydrogen-like ⁴⁰Ca-ions are reported. The obtained mass of the hydrogen-like and lithium-like ion is 39.952181819(29) u and 39.953272223(24) u, respectively. The corresponding mass of the ⁴⁰Ca atom is 39.962590858(22) u. This new value has a precision ten times higher than the literature value.     

Independent fission yields with JYFLTRAP

A novel method to determine independent yields in proton induced fission employing ion counting after a Penning trap has been developed. A satisfactory agreement with previous measurements was found for independent yields of Cs isotopes in 50 MeV proton induced fission.     

ISOLTRAP: An on-line Penning trap for mass spectrometry on short-lived nuclides

ISOLTRAP is a Penning trap mass spectrometer for high-precision mass measurements on short-lived nuclides installed at the on-line isotope separator ISOLDE at CERN. The masses of close to 300 radionuclides have been determined up to now. The applicability of Penning trap mass spectrometry to mass measurements of exotic nuclei has been extended considerably at ISOLTRAP by improving and developing this double Penning trap mass spectrometer over the past two decades. The accurate determination of nuclear binding energies far from stability includes nuclei that are produced at rates less than 100 ions/s and with half-lives well below 100ms. The mass-resolving power reaches 10⁷ corresponding to 10keV for medium heavy nuclei and the uncertainty of the resulting mass values has been pushed down to below 10^-8. The article describes technical developments achieved since 1996 and the present performance of ISOLTRAP.     

Accurate mass measurements of very short-lived nuclei

Mass measurements of ³⁴Ar, ^73-78Kr, and ^74,76Rb were performed with the Penning-trap mass spectrometer ISOLTRAP. Very accurate Q _EC-values are needed for the investigations of the t-value of 0⁺ → 0⁺ nuclear β-decays used to test the standard model predictions for weak interactions. The necessary accuracy on the Q _EC-value requires the mass of mother and daughter nuclei to be measured with δm/m ⩽ 3 ^. 10^-8. For most of the measured nuclides presented here this has been reached. The ³⁴Ar mass has been measured with a relative accuracy of 1.1 ^. 10^-8. The Q _EC-value of the ³⁴Ar 0⁺ → 0⁺ decay can now be determined with an uncertainty of about 0.01%. Furthermore, ⁷⁴Rb is the shortest-lived nuclide ever investigated in a Penning trap. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: frank.herfurth@cern.ch     

Light-ion-induced reactions in mass measurements of neutron-deficient nuclides close to A = 100

A survey of neutron-deficient nuclides which can be produced via proton- and ³He -induced fusion-evaporation reactions in the A = 100 region was made using a Penning trap as a high-resolution mass filter. A comparison of the measured isotopic rates with a statistical model calculation for the proton-induced reactions shows the importance of using the precise binding energy values for the final reaction products. In particular, proton separation energies were found to play an important role in the evaporation process. In addition, accurate masses of 12 nuclides, ^{97-99, 101}Pd , ¹⁰⁰Ag , ^101-105Cd and ^{102, 104}In , were determined with uncertainties of less than 10keV.     

Direct mass measurements of exotic nuclei

The present status and recent results from direct mass measurements of exotic nuclei are presented. ISOL, in-flight, and combined facilities provide a wide variety of nuclides far-off stability covering a wide range of half-lives down to the sub-millisecond region. Modern direct mass measurements are carried out using frequency and time-of-flight techniques. The obtained accurate mass data point to nuclear-structure phenomena and serve as a basis for astrophysical and weak-interaction studies. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: c.scheidenberger@gsi.de     

From direct to absolute mass measurements: A study of the accuracy of ISOLTRAP

For a detailed study of the accuracy of the Penning trap mass spectrometer ISOLTRAP all expected sources of uncertainty were investigated with respect to their contributions to the uncertainty of the final result. In the course of these investigations, cross-reference measurements with singly charged carbon clusters ¹²C⁺ _n were carried out. The carbon cluster ions were produced by use of laser-induced desorption, fragmentation, and ionization of C₆₀ fullerenes and injected into and stored in the Penning trap system. The comparison of the cyclotron frequencies of different carbon clusters has provided detailed insight into the residual systematic uncertainty of ISOLTRAP and yielded a value of 8×10^-9. This also represents the current limit of mass accuracy of the apparatus. Since the unified atomic mass unit is defined as 1/12 of the mass of the ¹²C atom, it will be possible to carry out absolute mass measurements with ISOLTRAP in the future. Received 7 June 2002 Published online 6 November 2002 RID="a" ID="a"e-mail: a.kellerbauer@cern.ch RID="b" ID="b"Current address: Centre de Physique des Particules de Marseille, 13288 Marseille Cedex 9, France.     

High-precision mass measurements of hydrogen-like <Superscript>24</Superscript>Mg<Superscript>11+</Superscript> and <Superscript>26</Superscript>Mg<Superscript>11+</Superscript> ions in a Penning trap

For the determination of the bound-electron g factor in hydrogen-like heavy ions the mass of the ion is needed at a relative uncertainty of at least 1 ppb. With the SMILETRAP Penning trap mass spectrometer at the Manne Siegbahn Laboratory in Stockholm several mass measurements of ions with even-even nuclei at this level of precision have been performed so far, exploiting the fact that the mass precision increases linearly with the ion charge. Measurements of masses of the hydrogen-like ions of the two Mg-isotopes ²⁴Mg and ²⁶Mg are reported. The masses of the hydrogen-like ions are 23.979011054(14) u and 25.976562354(34) u, corresponding to the atomic masses 23.985041690(14) u and 25.982592986(34) u, respectively. The possibility to use these two isotopes for the first observation of an isotope effect in the bound-electron g factor in hydrogen-like heavy ions is discussed.     

Carbon clusters for absolute mass measurements at ISOLTRAP

The cyclotron frequencies of singly charged carbon clusters C_n ⁺ (n ≥ 2) were measured with the Penning-trap mass spectrometer ISOLTRAP at ISOLDE/CERN. The present limit of mass accuracy δm/m = 1.2 ^. 10^-8 and the extent of the mass-dependent systematic shift (δm/m)_sys = 1.7(0.6) ^. 10^-10/u ^. (m - m _ref) of the setup were investigated for the first time. In addition, absolute mass measurements by use of pure clusters of the most abundant carbon isotope ¹²C are now possible at ISOLTRAP. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"Present address: CERN, CH-1211 Geneva 23, Switzerland; e-mail: klaus.blaum@cern.ch     

Development of a Fourier-Transform Ion-Cyclotron-Resonance detection for short-lived radionuclides at SHIPTRAP

The Penning-trap mass spectrometer SHIPTRAP at GSI is designed to provide clean and cooled beams of singly charged radioactive ions produced in fusion-evaporation reactions and separated in-flight by the velocity filter SHIP. The scientific goals include mass spectrometry, atomic and nuclear spectroscopy, and chemistry of transuranium species which are not available at ISOL- or fragmentation facilities Penning-trap based mass measurements on radionuclides relies up to now on the destructive time-of-flight ion-cyclotron-resonance method. One of the main limitations to the experimental investigations is the low production rate of most of these exotic nuclides, for which the use of this detection scheme is not applicable. A sensitive and non-destructive method, like the narrow-band Fourier Transform ion-cyclotron-resonance technique, is ideally suited for the identification and characterization of these species. A new cryogenic trap setup for SHIPTRAP exploiting this detection technique as well as some results of first preparatory tests are presented.     

The status of the Super-FRS at FAIR

The Super-FRS will be a large-acceptance two-stage superconducting fragment separator with three exit branches serving different experimental areas. Due to the high primary-beam intensity of up to 10¹² ions/s a challenging design of the target area and the components used in the first dipole Super-FRS is necessary. These efforts include high-power production targets, beam-dumps to catch the remaining primary beam, and radiation resistant magnets. In this contribution we summarize the recent developments on these issues.     

Accurate masses of unstable rare-earth isotopes by ISOLTRAP

Direct mass measurements of neutron-deficient rare-earth isotopes in the vicinity of ¹⁴⁶Gd were performed with the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN. This paper reports on the measurement of more than 40 isotopes of the elements praseodymium, neodymium, promethium, samarium, europium, dysprosium and holmium, that have been measured with a typical accuracy of m 14 keV. An atomic mass evaluation has been performed taking into account other experimental mass values via a least-squares adjustment. The results of the adjustment are discussed. Received: 18 April 2000 / Accepted: 12 July 2000     

The symmetry energy in nuclei and in nuclear matter

We discuss to what extent information on ground-state properties of finite nuclei (energies and radii) can be used to obtain constraints on the symmetry energy in nuclear matter and its dependence on the density. The starting point is a generalized Weizs?cker formula for ground-state energies. In particular, effects from the Wigner energy and shell structure on the symmetry energy are investigated. Strong correlations in the parameter space prevent a clear isolation of the surface contribution. Use of neutron skin information improves the situation. The result of the analysis appears consistent with a rather soft density dependence of the symmetry energy in nuclear matter.     

Tokai Radioactive Ion Accelerator Complex (TRIAC)

An ISOL-based radioactive nuclear beam (RNB) facility, Tokai Radioactive Ion Accelerator Complex (TRIAC), has been jointly developed by High Energy Accelerator Research Organization (KEK) and Japan Atomic Energy Agency (JAEA). The facility started to supply RNBs for experiments in 2005 and RNBs including fission fragments with energies up to 1.1MeV/A are available in the present. Several experimental studies were performed successfully using ⁸Li beams with various energies.     

Generalized hybrid derivative coupling model for finite nuclei

The generalized hybrid derivative coupling model has been applied to explore various ground state properties of different nuclei. In this work we have confined our calculation only to the model characterized by the hybridization parameter α = 1/4 which gives better results than the other models of the same class, as we have seen earlier, for nuclear matter calculations. The binding energy, single-particle energy spectra, density and charge radii of different doubly closed nuclei like ¹⁶O, ⁴⁰Ca, ⁴⁸Ca, ⁹⁰Zr, ¹³²Sn, ²⁰⁸Pb have been studied. The success of this model, in describing the doubly closed nuclei, motivates us to extend this calculation further in the case of open shell nuclei after incorporating the pairing interaction and using a BCS transformation. We have calculated the binding energy for such nuclei. We have also studied the isotopic shift for different Pb isotopes with respect to ²⁰⁸Pb. We have compared our results with the other standard theoretical results as well as with the experimental values. Received: 18 August 2000 / Accepted: 13 April 2001     

Precise atomic masses of neutron-rich Br and Rb nuclei close to the r-process path

The Penning trap mass spectrometer JYFLTRAP, coupled to the Ion-Guide Isotope Separator On-Line (IGISOL) facility at Jyv?skyl?, was employed to measure the atomic masses of neutron-rich ^85-92Br and ^94-97Rb isotopes with a typical accuracy less than 10keV. Discrepancies with the older data are discussed. Comparison to different mass models is presented. Details of nuclear structure, shell and subshell closures are investigated by studying the two-neutron separation energy and the shell gap energy.     

Calculating damping effects for the ion motion in a Penning trap

In this note a simple idea is suggested to calculate the effect of damping on the ion motion in a Penning trap. The analysis is restricted to the experimentally important special case that the axial motion (z-direction) is not coupled to that in the xy-plane, so that both motions can be treated separately. The method views the cyclotron frequency ω_c as a complex variable that can be continued analytically from real values (undamped case) into the complex plane. The power of the approach becomes obvious in connection with advanced problems such as the calculation of line profiles for quadrupole excitation.