Hyperfine structure and isotope shift measurements on 235U and laser separation of uranium isotopes by two-step photoionization

Two-step photoionization of an atomic beam and quadrupole mass analysis have been used for the precise measurement of the isotope shift between uranium isotopes 235 and 238 and the hyperfine structure of ²³⁵U. For the 5915 Å ground-state transition 15 hfs components were found. The residual atomic beam was isotopically enriched by factors 2.5 and 10 for ²³⁵U and ²³⁸U, respectively.     

Separation of Isotopes of Lithium and Uranium by Electromigration Using Cation-Exchange Membranes

Isotope separation by chromatographic electromigration has been studied for lithium (⁶Li and ⁷Li) and uranium (²³⁵U and ²³⁸U), using cation-exchange membranes as migration media. The membranes were pulled back against the direction of the movement of isotopic cations in a countercurrent manner. In both cases of the elements the lighter isotope, ⁶Li or ²³⁵U, was concentrated at the frontal part of a migration zone; at the extreme front the ⁶Li atom % increased to 16.8% from the original value of 7.5% after 386 cm migration, and the ²³⁵ U atom % rose to 0.743% from the original value of 0.723% after 200 cm migration. Isotope separation coefficients were experimentally determined: ε = (3.7 ± 0.4) μ 10^?3 for lithium isotopes, and two slightly different values ε = (4.9 ± 1.0) μ 10^?5 and (5.4 ± 1.1) μ 10^?5 for uranium isotopes. The steep isotope accumulation was observed in a narrow boundary region. A mathematical expression for the isotope accumulation curve was derived, and the slope of the curve was assessed for each experimental result.     

Isotope shifts of the ground state of neon: Refining the measurement results

Abstract—It has been revealed that the published results of measurements of the isotope shift of the ground state of even neon isotopes contain systematic errors. The errors are caused by the use of erroneous data regarding the absolute values of specific mass shifts of excited states and by the measurement errors of the isotope shifts themselves for transitions to the ground state. The isotope shift of the 2p⁵4s[3/2]₁ → 2p⁶(¹S₀) transition has been measured to be 2305 ± 20 MHz, the absolute specific mass shift of the 3p[3/2]₂: (2_р9) level has been determined to be 647 ± 10 MHz, and the isotope shift of the ground state has been found to be–3156 ± 30 MHz.     

Excited states of 154Nd studied through the decay of 154Pr

The neutron-rich isotope ¹⁵⁴Pr, the heaviest isotope of praseodymium, has been investigated by γ-ray multispectrum scaling and γ-γ-(t), X-γ-(t) coincidence experiments. The isotope ¹⁵⁴Pr was separated from ²³⁵U fission products with the on-line isotope separator KUR-ISOL. The decay scheme of ¹⁵⁴Pr has been constructed consisting of 9 excited states and 12 transitions in ¹⁵⁴Nd, including 7 excited states newly found in the present experiment.     

Isotope shifts for the P,Q, R lines in indium-doped silicon

We have measured the isotope shift of the P and R luminescence lines in Si doped with In and diffused with isotopically enriched Fe. We find no measurable shift in the R line. Similar experiments on the luminescence lines attributed to an isolated Fe complex show no shift in the previously identified “phonon replicas.” Theoretical calculations of defect phonon resonances near 9 meV for interstitial and substitutional Fe predict an isotope shift of 0.17 meV for ⁵⁶Fe and ⁵⁴Fe. This value is in disagreement with the observed lack of a shift.     

Isotope shift and hyperfine structure of the highly excited atomic uranium

The laser induced fluorescence method using atomic beam combined with Doppler-free two-photon absorption technique was applied for the measurement of isotope shifts and hyperfine structures of atomic uranium including ²³⁴U, ²³⁵U, ²³⁶U and ²³⁸U isotopes. The isotope shifts between ²³⁸U-²³⁴U, ²³⁸U-²³⁵U, ²³⁸U-²³⁶U, and the hyperfine structure of ²³⁵U were obtained in the high lying odd levels around 4 eV. Received 3 December 2001 / Received in final form 4 July 2002 Published online 29 October 2002 RID="a" ID="a"e-mail: oba@analchem.tokai.jaeri.go.jp     

Isomer-shift analogue in neutron resonances

For the first time, the recently predicted chemical shift of neutron resonances, to be regarded as an analogue to the Mössbauer isomer shift, has been experimentally observed studying the 6.67 eV resonance of ²³⁸U. The experimental shifts were determined by a chi-square fitting technique from the time-of-flight transmission spectra of metallic uranium and four uranium compounds measured at the Dubna IBR-30 pulsed reactor. A computational method has been applied to estimate, and compensate for, the influence of the crystal-lattice vibrations on the experimental values thus obtained. The electron density differences at the nucleus have been calculated for the various sample pairs using available data on chemical X-ray shifts in uranium compounds, on Mössbauer isomer shifts in isovalent neptunium compounds and on free-ion electron densities. The resonance shift results lead to the conclusion that the mean-square charge radius of ²³⁸U diminishes by 1.7_?0.8^+1.2 fm² upon capturing the resonance neutron.     

Isotope shift measurements in the atomic spectrum of lanthanum (LaI)

Using the reactor-produced lanthanum isotope ₅₇ ¹³⁷ La, the highly enriched rare ₅₇ ¹³⁸ La and the stable ₅₇ ¹³⁹ La, the isotope shift has been measured in five lines of the La I-spectrum with the aid of a pressure-scanned Fabry-Pérot interferometer. The isotope shift data obtained show surprisingly large specific mass effects, arising from configuration mixing of levels with a 4f electron involved. The changes in mean square charge radiusδ〈r ²〉 of these nuclei extracted from the experimental isotope shift constants C_exp are compared with the corresponding values for the isotonic barium nuclei, where similar anomalies in the isotope shifts occur.     

Theory of Isotope Effects on He+ Trapping in Solid Hydrogen

We are currently investigating the influence of vibrational effects on the strength of trapping of He⁺ in solid hydrogen. Such effects can lead to an isotope dependence of the trapping energy associated with the hydrogen molecules and He⁺ ion. At the present time, our focus is on the isotope effect for ³He⁺ and ⁴He⁺, which we are studying through the vibrational motions of the trapped He⁺ ions in the potential they experience as they move about their equilibrium positions. The potential governing the vibrations has been obtained from Hartree–Fock cluster calculations of the total energy of the cluster composed of the He⁺ ion and up to the third nearest neighbor hydrogen molecules as a function of the displacement of the He⁺ ion from its trapped position. The energy eigenvalues for the ground vibrational states of ³He⁺ and ⁴He⁺ in this potential come out as 1.29 and 0.96 meV, respectively, leading to corresponding reductions by these amounts in the binding energy of 8.6 eV for both ions without vibrational effects. The difference of these reductions can be considered as an isotope shift, its value for this case being 0.33 meV. From the analysis for these results, it is suggested that isotope shift effects for deuteron and triton in solid D–T would have the same order of magnitude. A procedure for more accurate investigations of the isotope shifts is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

First Measurement of the Nuclear Charge Radii of Short-Lived Lithium Isotopes

A novel method for the determination of nuclear charge radii of lithium isotopes is presented. Precise laser spectroscopic measurements of the isotope shift in the lithium 2s → 3s transition are combined with highly accurate atomic physics calculation of the mass dependent isotope shift to extract the charge-distribution-sensitive information. This approach has been used to determine the charge radii of ^8,9Li for the first time.     

Nuclear charge radius,spin and nuclear moments of45Ca by laserspectroscopy

The mean square charge radius, the spin, the magnetic moment and the quadrupole moment of the⁴⁵Ca nucleus have been determined from the isotope shift in the Ca- intercombination line and from the hyperfine structure splitting of the 4s4p³P₁. state. A highly sensitive laserspectroscopic technique in combination with an atomic beam was used in the experiment.     

Isotope shift in Ni I and changes in mean-square nuclear charge radii of the stable Ni isotopes

The isotope shift in the Ni I spectrum was studied in 17 lines for all stable isotopes by means of a photoelectric recording Fabry-Perot spectrometer with digital data processing. The measured isotope shifts were separated into mass shift and field shift by comparing the optical isotope shift with model-independent δ〈r ²〉 values derived from a combined elastic electron scattering and muonic x-ray data analysis. The ratios of the observed field shifts in different types of transitions could be explained quantitatively by Hartree-Fock calculations. The relative changes in mean-square nuclear charge radii were found to be: [58, 60] 1.293(15); [60, 62]1; [62, 64] 0.641(16); [60, 61] 0.382(9). The absolute value δ〈r ²〉^60,62=0.170(35) fm² was derived using fine structure as well as hyperfine structure data for the determination of the change in the electron charge density at the nucleus in 4s-4p transitions.     

Relativistic J-dependence of the isotope shift in the 6s-6p doublet of Ba II

The collinear laser-ion beam technique has been used to measure the isotope shift and hyperfine structure in the 6s-6p doublet (4,934Å, 4,554Å) of Ba II for all seven stable isotopes. The influence of the excited² P _1/2 and² P _3/2 states on the field shift leads to a difference of 2.5(3)% in the electronicF factors. The specific mass shifts differ by {A′-A} 2.2(3) MHz which corresponds to about 12% of the normal mass shift.     

Identification of a new isotope154Pr

The heaviest isotope of praseodymium,¹⁵⁴Pr, has been identified for the first time by γ-ray measurements of mass-separated activities obtained from a He-jet type on-line isotope separator for fission products of²³⁵U. The Nd-K X-rays and 10 γ-rays have been assigned to be generated by the β-decay of¹⁵⁴Pr. The half-life has been determined to be 2.3(1) s, which is not far from the theoretical predictions of 1.5 s and 4.0 s.     

Nouvelle methode de detection des resonances optiques par deviation magnetique d'un jet atomique

We propose a method to be used in the investigation of the hyperfine structure and isotope shift of ²⁵Na. This method has been tested with a ²³Na beam and the limit of the signal-to-noise ratio expected with this method is discussed.     

Measurement of isotope shift and hyperfine splitting of190, 191, 193, 197Pb isotopes by collinear laser spectroscopy

We report here on the measurement of isotope shift and hyperfine splitting of^{190, 191, 193, 197}Pb for the 723 nm atomic optical transition. Detailed analysis of the optical data has been done by combining them with the available muonic and electronicx-ray isotope shift data. The magnetic dipole moments and the electric quadrupole moments of the odd isotopes have been extracted from the hyperfine coupling constants of the atomic states involved in the optical transition used.     

Isotope shift measurements of muonic X-rays in134, 136, 138Barium

The isotope shifts of muonic X-rays for the three stable Ba-isotopes^{134, 136, 138}Ba have been measured with high accuracy. Especially the differences in the rms radiiΔ〈r ²〉 have been determined in a model independent way and have been used to calibrate optical isotope shift data.     

Experimental and theoretical investigation of the isotope shift of the 4D level in atomic potassium

Doppler-free two-photon laser spectroscopic measurements in the deep red spectral region have been performed on the transition 4² S _1/2→4² D _J in the naturally abundant isotopes 39 and 41 of atomic potassium. The 4D level isotope shift, ?81±12 MHz was obtained by combining the current results with data from Rydberg-state spectroscopy. Many-body perturbation theoretical calculations of the specific mass shift in the measured state are also presented. With the use of Brueckner orbitals the value ?70 MHz was obtained in substantial agreement with the experimental result.     

High resolution spectroscopy of rydberg states in indium I

Two-photon laser spectroscopy in a dense indium vapour allowed to investigatenp ² P _{1/2, 3/2} states (n=27–35) for^{113, 115}In with a thermionic diode. Precise data on the fine structure splitting of these states and the isotope shift of the two photon transitions have been obtained. The fine structure splitting shows a hydrogenic behaviour. By using the result of our isotope shift measurement in combination with literature values, level isotope shifts with reference to the ionization limit are deduced and analysed with respect to the different contributions.     

Isotope shift and configuration mixing in dysprosium II

The isotope shift in the spark spectrum of dysprosium was studied by means of a photoelectric recording Fabry-Perot spectrometer with digital data output. For 29 lines the isotope shift of¹⁶²Dy and¹⁶⁴Dy was measured in order to check the mixing of the three configurations 4f ⁹5d6s, 4f ⁹5d ², and 4f ¹⁰6p calculated by Wyart. By means of the sharing rule the configuration mixing could be confirmed as a whole. In the ground state configuration the influence of relativistic effects was demonstrated and explained by theory. The order of magnitude of crossed-second-order effects contributing to the isotope shift of 4f ¹⁰6s⁶ I and⁴ I could be estimated. In three lines the isotope shift of all stable Dy isotopes was measured. Mass shift and field shift were separated by comparison with results obtained in the arc spectrum.