Showing papers by "Lutz Schweikhard published in 2008"

First Penning Trap Mass Measurements beyond the Proton Drip Line

Abstract: The masses of six neutron-deficient rare holmium and thulium isotopes close to the proton drip line were determined with the SHIPTRAP Penning trap mass spectrometer. For the first time the masses of the proton-unbound isotopes {sup 144,145}Ho and {sup 147,148}Tm were directly measured. The proton separation energies were derived from the measured mass values and compared to predictions from mass formulas. The new values of the proton separation energies are used to determine the location of the proton drip line for holmium and thulium more accurately.

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

Abstract: 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.

Mass measurements in the vicinity of the r p-process and the nu p-process paths with the Penning trap facilities JYFLTRAP and SHIPTRAP

Abstract: The masses of very neutron-deficient nuclides close to the astrophysical r p- and {nu} p-process paths have been determined with the Penning trap facilities JYFLTRAP at JYFL/Jyvaeskylae and SHIPTRAP at GSI/Darmstadt. Isotopes from yttrium (Z=39) to palladium (Z=46) have been produced in heavy-ion fusion-evaporation reactions. In total, 21 nuclides were studied, and almost half of the mass values were experimentally determined for the first time: {sup 88}Tc, {sup 90-92}Ru, {sup 92-94}Rh, and {sup 94,95}Pd. For the {sup 95}Pd{sup m}, (21/2{sup +}) high-spin state, a first direct mass determination was performed. Relative mass uncertainties of typically {delta}m/m=5x10{sup -8} were obtained. The impact of the new mass values has been studied in {nu} p-process nucleosynthesis calculations. The resulting reaction flow and the final abundances are compared with those obtained with the data of the Atomic Mass Evaluation 2003.

Masses and charge radii of 17-22Ne and the two-proton-halo candidate 17Ne.

Abstract: High-precision mass and charge radius measurements on $^{17--22}\mathrm{Ne}$, including the proton-halo candidate $^{17}\mathrm{Ne}$, have been performed with Penning trap mass spectrometry and collinear laser spectroscopy. The $^{17}\mathrm{Ne}$ mass uncertainty is improved by factor 50, and the charge radii of $^{17--19}\mathrm{Ne}$ are determined for the first time. The fermionic molecular dynamics model explains the pronounced changes in the ground-state structure. It attributes the large charge radius of $^{17}\mathrm{Ne}$ to an extended proton configuration with an ${s}^{2}$ component of about 40%. In $^{18}\mathrm{Ne}$ the smaller radius is due to a significantly smaller ${s}^{2}$ component. The radii increase again for $^{19--22}\mathrm{Ne}$ due to cluster admixtures.

Mass measurements beyond the major r-process waiting point 80Zn.

Abstract: High-precision mass measurements on neutron-rich zinc isotopes (71m,72-81)Zn have been performed with the Penning trap mass spectrometer ISOLTRAP. For the first time, the mass of 81Zn has been experimentally determined. This makes 80Zn the first of the few major waiting points along the path of the astrophysical rapid neutron-capture process where neutron-separation energy and neutron-capture Q-value are determined experimentally. The astrophysical conditions required for this waiting point and its associated abundance signatures to occur in r-process models can now be mapped precisely. The measurements also confirm the robustness of the N=50 shell closure for Z=30.

Restoration of the N=82 shell gap from direct mass measurements of Sn-132,Sn-134

Abstract: A high-precision direct Penning trap mass measurement has revealed a 0.5-MeV deviation of the binding energy of (134)Sn from the currently accepted value. The corrected mass assignment of this neutron-rich nuclide restores the neutron-shell gap at N=82, previously considered to be a case of "shell quenching." In fact, the new shell gap value for the short-lived (132)Sn is larger than that of the doubly magic (48)Ca which is stable. The N=82 shell gap has considerable impact on fission recycling during the r process. More generally, the new finding has important consequences for microscopic mean-field theories which systematically deviate from the measured binding energies of closed-shell nuclides.

Mass Measurements beyond the Majorr-Process Waiting PointZn80

Abstract: High-precision mass measurements on neutron-rich zinc isotopes $^{71m,72--81}\mathrm{Zn}$ have been performed with the Penning trap mass spectrometer ISOLTRAP. For the first time, the mass of $^{81}\mathrm{Zn}$ has been experimentally determined. This makes $^{80}\mathrm{Zn}$ the first of the few major waiting points along the path of the astrophysical rapid neutron-capture process where neutron-separation energy and neutron-capture $Q$-value are determined experimentally. The astrophysical conditions required for this waiting point and its associated abundance signatures to occur in $r$-process models can now be mapped precisely. The measurements also confirm the robustness of the $N=50$ shell closure for $Z=30$.

Mass measurements and evaluation around A = 22

Abstract: Frequency ratio measurements with different combinations of the singly charged ions from 21, 22, 23Na , 22, 24Mg , and 37, 39K were performed at the on-line Penning trap mass spectrometer ISOLTRAP, CERN, Geneva. The masses and mass differences were deduced with a relative uncertainty of about or even below one part in 108 for the ions of interest using a least-squares analysis of all measured relations. The results have direct consequences for weak-interaction study as they give additional input to the test of CVC, and for nuclear astrophysics, because they help to establish the minimum observable signal for a NeNa cycle in a nova burst. We report here about the measurements and the detailed evaluation.

Towards a magnetic field stabilization at ISOLTRAP for high-accuracy mass measurements on exotic nuclides

Abstract: The field stability of a mass spectrometer plays a crucial role in the accuracy of mass measurements. In the case of mass determination of short-lived nuclides with a Penning trap, major causes of fluctuations are temperature variations in the vicinity of the trap and pressure changes in the liquid helium cryostat of the superconducting magnet. Thus systems for the temperature and pressure stabilization of the Penning trap mass spectrometer ISOLTRAP at the ISOLDE facility at CERN have been installed. A reduction of the temperature and pressure fluctuations by at least an order of magnitude down to Δ T ≈ ± 5 mK and Δ p ≈ ± 5 Pa has been achieved, which corresponds to a relative magnetic field change of Δ B / B = 2.7 × 10 - 9 and 1.1 × 10 - 10 , respectively.

Time-separated oscillatory fields for high-precision mass measurements on short-lived Al and Ca nuclides

Abstract: High-precision Penning trap mass measurements on the stable nuclide 27Al as well as on the short-lived radionuclides 26Al and 38,39Ca have been performed by use of radiofrequency excitation with time-separated oscillatory fields, i.e. Ramsey's method, recently extended to Penning trap mass measurements of radioactive isotopes. A comparison with the conventional method of a single continuous excitation demonstrates the advantage of up to ten times shorter measurements. The new mass values of 26,27Al are compared to literature values and clarify conflicting data in this mass region. In addition, the resulting mass values of the superallowed β-emitter 38Ca as well as of the ground state of the β-emitter 26Alm confirm previous measurements.

X-Ray Signature of Charge Exchange in the Spectra of L-Shell Iron Ions

Abstract: The X-ray signature of charge exchange between highly charged L-shell iron ions and neutral gas atoms was studied in the laboratory in order to assess its diagnostic utility. Significant differences with spectra formed by electron-impact excitation were observed. In particular, a strong enhancement was found of the emission corresponding to -->n ≥ 4→ n = 2 transitions relative to the -->n = 3→ n = 2 emission. This enhancement was detectable even with relatively low-resolution X-ray instrumentation -->(E/Δ E ≈ 10) and may enable future identification of charge exchange as a line-formation mechanism in astrophysical spectra.

Masses of short-lived nuclides: precision measurement techniques and applications.

Abstract: Similar to fingerprints, atoms can be identified by their masses—when weighted with sufficient accuracy. The mass of an atom reflects all internal forces and thus carries information on the strong,...

Mass measurements of short‐lived isotopes in a penning trap

Abstract: A mass spectrometer has been set up at the on‐line isotope separator ISOLDE at CERN/Geneva. Mass‐separated radioactive ions are stored in a Penning trap. Their mass is determined by a measurement of the cyclotron frequency in the magnetic field of a superconducting magnet. A resolving power of up to 300.000 and a precision of some 10 keV were determined in case of mass measurements of neutron‐deficient RB and Cs isotopes. The resonance of the isobars 88Sr and 88Rb were clearly resolved and evidence was obtained for an isomer in 122Cs.

Photofragmentation of stored cluster ions

Abstract: Small metal clusters were produced by laser desorption and transferred into a Penning trap. They were illuminated by a 20‐ns dye‐laser pulse and electronically excited. Relaxation channels were investigated in the case of positively charged gold and silver clusters evaporation of neutral atoms or dimers (depending on photon energy and number of cluster atoms) was observed. Photoabsorption cross section measurements of Au9+. For Au21+ yield a resonance similar to the one already known for Ag9+. For Au21+ and Ag21+ a delayed photofragmentation in the millisecond range has been observed.