0000000000657301
AUTHOR
Ch. Geppert
Frequency-comb-based measurements of lithium and beryllium isotopes for nuclear structure studiesThis paper was presented at the International Conference on Precision Physics of Simple Atomic Systems, held at University of Windsor, Windsor, Ontario, Canada on 21–26 July 2008.
We report on the measurement of the 2s-3s transition frequencies in the stable lithium isotopes and 2s-2p isotope shift measurements of 7,9,10,11Be, using a femtosecond frequency comb. For the beryllium isotopes, we extract the changes in the mean-square nuclear charge radius along the isotope chain by comparison with high-precision atomic mass shift calculations. The 2s-3s transition frequency is compared with theoretical calculations, and possibilities to extract an absolute value for the nuclear charge radius of lithium isotopes are discussed.
A highly selective laser ion source for bunched, low emittance beam release
A novel type of resonance ionization laser ion source (RILIS) is under development, which combines the advantages of laser ionization with those of a source-implemented ion trap. This laser ion source trap (LIST) system, based on a gas-filled linear radio-frequency quadrupole ion trap, decouples the evaporation and ionization process by introduction of a primary surface ion repeller. Apart from significantly enhancing the selectivity in radioactive ion beam production, optimum control on the temporal pulse structure and the emittance of the generated laser ion bunch is obtained. A variety of operational modes from quasi-dc to microseconds-bunched ion beams with variable repetition rate can …
Laser resonance ionization for efficient and selective ionization of rare species
Abstract Due to the steady development and refinement of powerful pulsed as well as continuous-wave lasers, resonance ionization has developed into an extremely versatile tool for numerous applications. Apart from suppressing isobaric interferences and contributing to isotopic selectivity already in the ionization process, resonant optical excitation and ionization with laser light ensures high overall efficiency and good temporal and spatial controls of the ions delivered to mass spectrometric applications. In the field of rare isotope research laser resonance ionization has nowadays become one of the key techniques, including similarly the determination of long-lived or stable ultra-trace…
Nuclear Charge Radius ofBe12
The nuclear charge radius of $^{12}\mathrm{Be}$ was precisely determined using the technique of collinear laser spectroscopy on the $2{s}_{1/2}\ensuremath{\rightarrow}2{p}_{1/2,3/2}$ transition in the ${\mathrm{Be}}^{+}$ ion. The mean square charge radius increases from $^{10}\mathrm{Be}$ to $^{12}\mathrm{Be}$ by $\ensuremath{\delta}⟨{r}_{c}^{2}{⟩}^{10,12}=0.69(5)\text{ }\text{ }{\mathrm{fm}}^{2}$ compared to $\ensuremath{\delta}⟨{r}_{c}^{2}{⟩}^{10,11}=0.49(5)\text{ }\text{ }{\mathrm{fm}}^{2}$ for the one-neutron halo isotope $^{11}\mathrm{Be}$. Calculations in the fermionic molecular dynamics approach show a strong sensitivity of the charge radius to the structure of $^{12}\mathrm{Be}$. Th…
Nuclear mean-square charge radii of63,64,66,68−82Ga nuclei: No anomalous behavior atN=32
Collinear laser spectroscopy was performed on the ${}^{63,64,66,68\ensuremath{-}82}$Ga isotopes with neutron numbers from $N=32$ to $N=51$. These measurements were carried out at the ISOLDE radioactive ion beam facility at CERN. Here we present the nuclear mean-square charge radii extracted from the isotope shifts and, for the lighter isotopes, new spin and moment values. New ground-state nuclear spin and moments were extracted from the hyperfine spectra of ${}^{63,70}$Ga, measured on an atomic transition in the neutral atom. The ground-state spin of ${}^{63}$Ga is determined to be $I=3/2$. Analysis of the trend in the change in mean-square charge radii of the gallium isotopes demonstrates …
Calibration of the ISOLDE acceleration voltage using a high-precision voltage divider and applying collinear fast beam laser spectroscopy
A high-voltage divider with accuracy at the ppm level and collinear laser spectroscopy were used to calibrate the highvoltage installation at the radioactive ion beam facility ISOLDE at CERN. The accurate knowledge of this voltage is particularly important for collinear laser spectroscopy measurements. Beam velocity measurements using frequencycomb based collinear laser spectroscopy agree with the new calibration. Applying this, one obtains consistent results for isotope shifts of stable magnesium isotopes measured using collinear spectroscopy and laser spectroscopy on laser-cooled ions in a trap. The long-term stability and the transient behavior during recovery from a voltage dropout were…
Development of a laser ion source at IGISOL
FURIOS, the Fast Universal laser IOn Source, is under development at the IGISOL (Ion Guide Isotope Separator On-Line) mass separator facility in Jyvaskyla, Finland. This new laser ion source will combine a state-of-the-art solid state laser system together with a dye laser system, for the selective and efficient production of exotic radioactive species without compromising the universality and fast release inherent in the IGISOL system. The motivation for, and development of, this ion source is discussed in relation to the programme of research ongoing at this mass separator facility.
Counting individual 41Ca atoms with a magneto-optical trap
Atom Trap Trace Analysis (ATTA), a novel method based upon laser trapping and cooling, is used to count individual atoms of 41Ca present in biomedical samples with isotopic abundance levels between 10^-8 and 10^-10. ATTA is calibrated against Resonance Ionization Mass Spectrometry, demonstrating a good agreement between the two methods. The present ATTA system has a counting efficiency of 2x10^-7. Within one hour of observation time, its 3-sigma detection limit on the isotopic abundance of 41Ca reaches 4.5x10^-10.
Hyperfine transition in209Bi80+—one step forward
The hyperfine transitions in lithium-like and hydrogen-like bismuth were remeasured by direct laser spectroscopy at the experimental storage ring. For this we have now employed a voltage divider which enabled us to monitor the electron cooler voltage in situ. This will improve the experimental accuracy by about one order of magnitude with respect to our previous measurement using the same technique.
Simple Nuclear Structure inCd111–129from Atomic Isomer Shifts
Isomer shifts have been determined in ^{111-129}Cd by high-resolution laser spectroscopy at CERN-ISOLDE. The corresponding mean square charge-radii changes, from the 1/2^{+} and the 3/2^{+} ground states to the 11/2^{-} isomers, have been found to follow a distinct parabolic dependence as a function of the atomic mass number. Since the isomers have been previously associated with simplicity due to the linear mass dependence of their quadrupole moments, the regularity of the isomer shifts suggests a higher order of symmetry affecting the ground states in addition. A comprehensive description assuming nuclear deformation is found to accurately reproduce the radii differences in conjunction wi…
Isotope shift of40,42,44,48Ca in the 4s2S1/2→ 4p2P3/2transition
We report on improved isotope shift measurements of the isotopes 40,42,44,48Ca in the 4s2S1/2→4p2P3/2 transition using collinear laser spectroscopy. Accurately known isotope shifts in the 4s2S1/2→4p2P1/2 (D1) transition were used to calibrate the ion beam energy with an uncertainty of ΔU ≈ ± 0.25 V. The accuracy in the D2 transition was improved by a factor of 5–10. A King-plot analysis of the two transitions revealed that the field shift factor in the D2 line is about 1.8(13)% larger than in the D1 transition which is ascribed to relativistic contributions of the 4p1/2 wave function.
Spins and magnetic moments of 58;60;62;64Mn ground states and isomers
The odd-odd 54;56;58;60;62;64Mn isotopes (Z = 25) were studied using bunched-beam collinear laser spectroscopy at ISOLDE, CERN. From the measured hyperfine spectra the spins and magnetic moments of Mn isotopes up to N = 39 were extracted. The previous tentative ground state spin assignments of 58;60;62;64Mn are now firmly determined to be I = 1 along with an I = 4 assignment for the isomeric states in 58;60;62Mn. The I = 1 magnetic moments show a decreasing trend with increasing neutron number while the I = 4 moments remain quite constant between N = 33 and N = 37. The results are compared to large-scale shell-model calculations using the GXPF1A and LNPS effective interactions. The excellen…
Time profile of ion pulses produced in a hot-cavity laser ion source.
The time spreads of Mn ions produced by three-photon resonant ionization in a hot-cavity laser ion source are measured. A one-dimensional ion-transport model is developed to simulate the observed ion time structures. Assuming ions are generated with a Maxwellian velocity distribution and are guided by an axial electric field, the predictions of the model agree reasonably well with the experimental data and suggest that the ions are radially confined in the ion source and a substantial fraction of the ions in the transport tube are extracted.
Spins and magnetic moments ofMn58,60,62,64ground states and isomers
The odd-odd $^{54,56,58,60,62,64}\mathrm{Mn}$ isotopes ($Z=25$) were studied using bunched-beam collinear laser spectroscopy at ISOLDE, CERN. From the measured hyperfine spectra the spins and magnetic moments of Mn isotopes up to $N=39$ were extracted. The previous tentative ground state spin assignments of $^{58,60,62,64}\mathrm{Mn}$ are now firmly determined to be $I=1$ along with an $I=4$ assignment for the isomeric states in $^{58,60,62}\mathrm{Mn}$. The $I=1$ magnetic moments show a decreasing trend with increasing neutron number while the $I=4$ moments remain quite constant between $N=33$ and $N=37$. The results are compared to large-scale shell-model calculations using the GXPF1A and…
Counting IndividualCa41Atoms with a Magneto-Optical Trap
Atom trap trace analysis, a novel method based upon laser trapping and cooling, is used to count individual atoms of $^{41}\mathrm{Ca}$ present in biomedical samples with isotopic abundance levels between ${10}^{\ensuremath{-}8}$ and ${10}^{\ensuremath{-}10}$. The method is calibrated against resonance ionization mass spectrometry, demonstrating good agreement between the two methods. The present system has a counting efficiency of $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$. Within 1 h of observation time, its $3\mathrm{\text{\ensuremath{-}}}\ensuremath{\sigma}$ detection limit on the isotopic abundance of $^{41}\mathrm{Ca}$ reaches $4.5\ifmmode\times\else\texttimes\fi{}{10…
Nuclear Charge Radius of $^{12}$Be
The nuclear charge radius of $^{12}$Be was precisely determined using the technique of collinear laser spectroscopy on the $2s_{1/2}\rightarrow 2p_{1/2, 3/2}$ transition in the Be$^{+}$ ion. The mean square charge radius increases from $^{10}$Be to $^{12}$Be by $\delta ^{10,12} = 0.69(5) \fm^{2}$ compared to $\delta ^{10,11} = 0.49(5) \fm^{2}$ for the one-neutron halo isotope $^{11}$Be. Calculations in the fermionic molecular dynamics approach show a strong sensitivity of the charge radius to the structure of $^{12}$Be. The experimental charge radius is consistent with a breakdown of the N=8 shell closure.
Tests of atomic charge-exchange cells for collinear laser spectroscopy
Abstract The performance characteristics of two charge-exchange cells (CECs) with horizontal and vertical cell configurations were determined by neutralizing a 10-keV rubidium ion beam in a potassium vapor. The neutralization efficiency and the fluorescence line shape of the 5s 2 S 1 / 2 ↔ 5 p 2P3/2 (D2) transition in neutral 85Rb were investigated as a function of the reservoir temperature used to control the potassium vapor density. The CECs exhibited similar neutralization performance and at neutralization efficiencies greater than 25–50% an asymmetric line shape of the rubidium D2 fluorescent signal was observed. The asymmetry was attributed to inelastic channels in the charge-exchange …
From Calcium to Cadmium: Testing the Pairing Functional through Charge Radii Measurements of Cd100−130
Differences in mean-square nuclear charge radii of $^{100--130}\mathrm{Cd}$ are extracted from high-resolution collinear laser spectroscopy of the $5s\text{ }{^{2}S}_{1/2}\ensuremath{\rightarrow}5p\text{ }{^{2}P}_{3/2}$ transition of the ion and from the $5s5p\text{ }{^{3}P}_{2}\ensuremath{\rightarrow}5s6s\text{ }{^{3}S}_{1}$ transition in atomic Cd. The radii show a smooth parabolic behavior on top of a linear trend and a regular odd-even staggering across the almost complete $sdgh$ shell. They serve as a first test for a recently established new Fayans functional and show a remarkably good agreement in the trend as well as in the total nuclear charge radius.
Peak shape for a quadrupole mass spectrometer: comparison of computer simulation and experiment
Abstract Computer simulations of ion trajectories have been used to evaluate the performance of a quadrupole mass spectrometer. Consideration has been given to realistic fields modeled on a commercial system as well as experimental distributions with respect to ion entry position, axial and radial velocity and relative phase of the quadrupole field. Determination of the mass filter acceptance-area as a function of the mass setting yields mass peak shapes with a dynamic range of more than seven orders of magnitude and thus provides estimates for abundance sensitivity. Results from these simulations are found to give excellent agreement with experimental measurements for different elements in…
High-resolution γ-ray spectroscopy: a versatile tool for nuclear β-decay studies at TRIUMF-ISAC
High-resolution γ-ray spectroscopy is essential to fully exploit the unique, high-quality beams available at the next generation of radioactive ion beam facilities such as the TRIUMF isotope separator and accelerator (ISAC). The 8π spectrometer, which consists of 20 Compton-suppressed HPGe detectors, has recently been reconfigured for a vigorous research programme in weak interaction and nuclear structure physics. With the addition of a variety of ancillary detectors it has become the world's most powerful device dedicated to β-decay studies. This paper provides a brief overview of the apparatus and highlights from recent experiments.
Selective ultra trace isotope determination in environmental and biomedical studies by high-resolution resonance ionization mass spectrometry
The precise determination of relative abundances of ultra trace isotopes in the range below 10 -9 is of importance for a wide spectrum of applications in fields like environmental protection, cosmo-chemistry, bio-medical tracer studies or geological and geo-chronological investigations. The necessary high isotopic selectivity, rather complete isobaric suppression and good overall efficiency for these investigations is provided by high-resolution resonance ionization mass spectrometry. Multi-step continuous wave laser excitation and ionization using diode lasers at a compact quadrupole mass spectrometer has been optimized to become a powerful and reliable experimental method, which is just b…
Isotope shifts and hyperfine structure in the transitions of gadolinium
High-resolution resonance ionization mass spectrometry has been used to measure isotope shifts and hyperfine structure in all (J = 2-6) and the transitions of gadolinium (Gd I). Gadolinium atoms in an atomic beam were excited with a tunable single-frequency laser in the wavelength range of 422-429 nm. Resonant excitation was followed by photoionization with the 363.8 nm line of an argon ion laser and resulting ions were mass separated and detected with a quadrupole mass spectrometer. Isotope shifts for all stable gadolinium isotopes in these transitions have been measured for the first time. Additionally, the hyperfine structure constants of the upper states have been derived for the isotop…
Changes in nuclear structure along the Mn isotopic chain studied via charge radii
The hyperfine spectra of $^{51,53-64}$Mn were measured in two experimental runs using collinear laser spectroscopy at ISOLDE, CERN. Laser spectroscopy was performed on the atomic $3d^5\ 4s^2\ ^{6}\text{S}_{5/2}\rightarrow 3d^5\ 4s4p\ ^{6}\text{P}_{3/2}$ and ionic $3d^5\ 4s\ ^{5}\text{S}_2 \rightarrow 3d^5\ 4p\ ^{5}\text{P}_3$ transitions, yielding two sets of isotope shifts. The mass and field shift factors for both transitions have been calculated in the multiconfiguration Dirac-Fock framework and were combined with a King plot analysis in order to obtain a consistent set of mean-square charge radii which, together with earlier work on neutron-deficient Mn, allow the study of nuclear struc…
High-voltage measurements on the 5 ppm relative uncertainty level with collinear laser spectroscopy
We present the results of high-voltage collinear laser spectroscopy measurements on the 5 ppm relative uncertainty level using a pump and probe scheme at the transition of involving the metastable state. With two-stage laser interaction and a reference measurement we can eliminate systematic effects such as differences in the contact potentials due to different electrode materials and thermoelectric voltages, and the unknown starting potential of the ions in the ion source. Voltage measurements were performed between −5 kV and −19 kV and parallel measurements with stable high-voltage dividers calibrated to 5 ppm relative uncertainty were used as a reference. Our measurements are compatible …
Three-step resonant photoionization spectroscopy of Ni and Ge: ionization potential and odd-parity Rydberg levels
In preparation of a laser ion source, we have investigated multi-step laser ionization via Rydberg and autoionizing states for atomic Ni and Ge using a mass separator with an ion beam energy of 20 keV. For both elements resonant three-step excitation schemes suitable for modern Ti:sapphire laser systems were developed. Rydberg series in the range of principal quantum numbers 20 n 80 were localized, assigned and quantum numbers were allocated to the individual resonances. Ionization potentials (IP) were extracted from fits of the individual series and quantum defects of individual levels were analysed for confirmation of series assignment. For Ni the ionization potential could be extracted w…
Properties and performance of a quadrupole mass filter used for resonance ionization mass spectrometry
Abstract The performance of commercial quadrupole mass spectrometers (QMS) with a number of imperfections, as compared to the ideal hyperbolic geometry, has been characterized using the computer simulation program simion 3d version 6.0. The analysis of simulated QMS geometries focuses primarily on modeling of the internal potential, the study of field deviations, and the influence of finite length on performance of the QMS. The computer simulation of ion trajectories in the QMS field yields predictions for optimum working conditions and provides estimates for the resolving power and the maximum isotopic abundance sensitivity. Experimental measurements that confirm these expectations are pre…
Intercomparison measurements between accelerator and laser based mass spectrometry for ultra-trace determination of 41Ca in the 10−11–10−10 isotopic range
Abstract Selective ultra-trace determination of the long-lived radioisotope 41 Ca has applications in environmental and biomedical research, as well as in cosmochemistry. We have conducted an intercomparison between the two currently available methods for measurement at these low (radio) activities: accelerator mass spectrometry (AMS) and resonance ionization mass spectrometry (RIMS). Three artificially produced 41 Ca samples, primarily of cosmochemical importance, with isotopic abundances in the range of 10 −11 –10 −10 were used and results of these measurements show good agreement between the two methods, within the experimental uncertainties.
COLLINEAR LASER SPECTROSCOPY ON NEUTRON-RICH Mn ISOTOPES APPROACHING N = 40
We have studied 51,53−64Mn (Z=25) via bunched-beam collinear laser spectroscopy at ISOLDE, CERN. Model-independent information on the ground- and isomeric state spins, as well as their g-factors is obtained from the measured hyperfine spectra. The spins are essential for further establishing the level schemes in the mass region, while the g-factors reveal the changing ground state wave functions in the Mn chain approaching N=40. ispartof: pages:699-702 ispartof: Acta Physica Polonica B vol:46 issue:3 pages:699-702 ispartof: location:Zakopane, Poland status: published
Laser ion source tests at the HRIBF on stable Sn, Ge and Ni isotopes
Abstract As one step in the ion source development for the Rare Isotope Accelerator, a hot-cavity laser ion source using an all-solid-state titanium–sapphire laser system has been tested at the Holifield Radioactive Ion Beam Facility. Resonance ionization of stable isotopes of Sn, Ge and Ni has been studied in a Ta hot cavity. Efficient three step resonant ionization schemes applying frequency tripling for the first excitation step and using auto-ionizing or atomic Rydberg states in the ionizing step have been identified for all three elements, resulting in laser ion beams of typically around 100 nA. By saturating most of the optical excitation steps involved, ionization efficiencies of 22%…
Nuclear Charge Radii ofMg21−32
Charge radii of all magnesium isotopes in the sd shell have been measured, revealing evolution of the nuclear shape throughout two prominent regions of assumed deformation centered on (24)Mg and (32)Mg. A striking correspondence is found between the nuclear charge radius and the neutron shell structure. The importance of cluster configurations towards N=8 and collectivity near N=20 is discussed in the framework of the fermionic molecular dynamics model. These essential results have been made possible by the first application of laser-induced nuclear orientation for isotope shift measurements.
Time profiles of ions produced in a hot-cavity resonant ionization laser ion source
Abstract The time profiles of Cu, Sn, and Ni ions extracted from a hot-cavity resonant ionization laser ion source are investigated. The ions are produced in the ion source by three-photon resonant ionization with pulsed Ti:Sapphire lasers. Measurements show that the time spread of these ions generated within laser pulses of about 30 ns duration could be larger than 100 μs when the ions are extracted from the ion source. A one-dimensional ion-transport model using the Monte Carlo method is developed to simulate the time dependence of the ion pulses. The prediction of the model agrees reasonably well with the experimental data. To reproduce the observed ion time profiles, we find it necessar…
Spin and magnetic moment of23Mg
A negative magnetic moment of 23Mg has been determined by collinear laser spectroscopy at CERN-ISOLDE. The absolute value is in agreement with previous measurements by nuclear magnetic resonance while the sign points at high-seniority configurations. The result is consistent with shell-model predictions for nuclei with valence nucleons in the sd shell. ispartof: Journal of Physics G, Nuclear and Particle Physics vol:44 issue:7 status: published
Laser spectroscopy of gallium isotopes beyond N = 50
The installation of an ion-beam cooler-buncher at the ISOLDE, CERN facility has provided increased sensitivity for collinear laser spectroscopy experiments. A migration of single-particle states in gallium and in copper isotopes has been investigated through extensive measurements of ground state and isomeric state hyperfine structures. Lying beyond the N = 50 shell closure, 82Ga is the most exotic nucleus in the region to have been studied by optical methods, and is reported here for the first time. ispartof: pages:012071-6 ispartof: Journal of Physics: Conference Series vol:381 issue:1 pages:012071-6 ispartof: Rutherford Centennial Conference on Nuclear Physics location:Manchester, UK dat…
Spins and electromagnetic moments of Cd101–109
The neutron-deficient cadmium isotopes have been measured by high-resolution laser spectroscopy at CERN-ISOLDE. The electromagnetic moments of $^{101}\mathrm{Cd}$ have been determined for the first time and the quadrupole-moment precision of $^{103}\mathrm{Cd}$ has been vastly improved. The results on the sequence of $5/{2}^{+}$ ground states in $^{101--109}\mathrm{Cd}$ are tentatively discussed in the context of simple structure in complex nuclei as similarities are found with the $11/{2}^{\ensuremath{-}}$ states in the neutron-rich cases. Comparison with shell-model calculations reveals a prominent role of the two holes in the $Z=50$ core.