Isotope shift measurements on the neutron-deficient thallium isotopes

Isotope shifts of the neutron-deficient thallium isotopes were measured on-line at the UNISOR mass separator. Spectroscopy was carried out using collinear fast beam laser spectroscopy in neutral thallium. The changes of the mean square charge radii were derived from the measurements. The changes in charge radii of the I=7 isotopes, including the newly measured¹⁸⁸Tl, are compared to the results in mercury and lead.     

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.     

Quadrupole collectivity of neutron-rich neon isotopes

The Angular Momentum Projected Generator Coordinate Method, with the quadrupole moment as collective coordinate and the Gogny force (D1S) as the effective interaction, is used to describe the properties of the ground state and low-lying excited states of the even-even neon isotopes ^20-34Ne, that is, from the stability valley up to the drip line. It is found that the ground state of the N = 20 nucleus ³⁰Ne is deformed but to a lesser extent than the N = 20 isotope of the magnesium. In the calculations, the isotope ³²Ne is at the drip line in good agreement with other theoretical predictions. On the other hand, rather good agreement with experimental data for many observables is obtained. Received: 19 Novemeber 2002 / Accepted: 24 January 2003 / Published online: 8 April 2003     

Study of neutron rich neon isotopes

The half-lives andP _n -values of the neutron rich isotopes^26–29Ne have been determined. The results are compared to shell-model calculations and good agreement is found except for²⁹Ne, where the half-life exceeds the predictions by more than an order of magnitude. This unexpectedly long half-life can be explained as due to a fp intruder configuration.     

Optical pumping of short lived Β-radioactive isotopes and the magnetic moment of37K

²¹Na (T _1/2=23 sec) and³⁷K(T _1/2=1.25 sec) have been produced in gas targets by (d, n) reactions and polarized by means of optical pumping or spin exchange scattering with optically pumped⁸⁷Rb. An asymmetry up to 3% in theΒ-decay of the polarized nuclei was found, which served to detect rf transitions between hfs levels of the atomic ground states of²¹Na and³⁷K.δF=0 andδF=1 resonances have been recorded, yielding spin, hfs separation and magnetic moment, especiallyI(³⁷K)=3/2,δW(³⁷K)=240.266 (3) Mc/sec andΜ _I(³⁷K)=0.02033(6) nm (diamagnetically corrected). For²¹Na earlier rf-spectroscopic data have been confirmed.     

Reorientation measurements on tungsten isotopes

In a particle-γ coincidence experiment, a thick tungsten target, of natural isotopic abundance, was bombarded with a and ¹⁶O beams. From analysis of the deexcitation γ-rays following Coulomb excitation, the spectroscopic quadrupole moment of the second 2⁺ state (the 22' state) was determined for ¹⁸⁶W and ¹⁸⁴W. In a separate Coulomb excitation experiment a thin, isotopically enriched ¹⁸⁶W target was bombarded with ¹⁶O ions. From analysis of projectiles scattered elastically and inelastically the quadrupole moment of the 2^+' state of ¹⁸⁶W was extracted. The results of the two experiments are in good agreement. The quadrupole moment of the 2^+' state is found to be opposite in sign to that of the first 2⁺ state for both isotopes studied. However, its magnitude decreases rapidly in going from ¹⁸⁶W to ¹⁸⁶W, in contrast to the predictions of the rotation-vibration or asymmetric rotor models. The microscopic theory of Kumar and Baranger does predict the experimental trend, qualitatively. Thus the present results are interpreted as being evidence of strong coupling between β and γ degrees of freedom in the tungsten isotopes, which, according to the theory of Kumar and Baranger, is the source of the reduced value of the quadrupole moment.     

Applications of the two-photon doppler-free method: Hyperfine interactions and isotope shift measurements

The hyperfine structures are generally of the same order of magnitude as the Doppler broadening of optical transitions and so are the isotopic shifts in the case of heavy elements. When these structures are too small, one must use Doppler-free methods. Among these methods, the two-photon spectroscopy has obtained good results in highly excited levels. In our laboratory in Paris, we did measurements on neon and helium by two-photon excitation from metastable levels. The precision of the measurements is of the order of one MHz, which permits a precise comparison with theory. We compare the measurements on neon with the theory by Liberman and we obtain a good fit in the first approximation, but must introduce mixing of wave functions for an exact explanation. In the case of helium, we obtain a good fit with the theoretical values obtained from the wave functions by Accad, Pekeris and Schiff. We also give an example where another technique by polarization measurements permits us to obtain experimentally a hyperfine structuresmaller than the natural width. We also present a short review of the measurements done by the two-photon method in other laboratories on other elements, Pb, Tl, In and alkaline earths Ca, Sr. Ba.     

Absolute frequency and isotope shift measurements of the cooling transition in singly ionized indium

We report greater than two orders of magnitude improvements in the absolute frequency and isotope shift measurements of the In⁺ 5s^{2 1}S₀ (F = 9/2)–5s5p ³P₁ (F = 11/2) transition near 230.6 nm. The laser-induced fluorescence from a single In⁺ in a radio-frequency trap is detected. The fourth-harmonic of a semiconductor laser is used as the light source. The absolute frequency is measured with the help of a frequency comb referenced to a Cs atomic clock. The resulting transition frequencies for isotopes ¹¹⁵In⁺ and ¹¹³In⁺ are measured to be 1 299 648 954.54(10) MHz and 1 299 649 585.36(16) MHz, respectively. The deduced cooling transition frequency difference is 630.82(19) MHz. By taking into account of the hyperfine interaction, the isotope shift is calculated to be 695.76(1.68) MHz.     

Hyperfine structure and isotope shift of the neutron-rich barium isotopes139–146Ba and148Ba

The hyperfme structure and isotope shift in the 6s ² S _1/2?6p ²P_3/2 line of Ba II (455.4 nm) have been measured by collinear fast-beam laser spectroscopy for the neutron-rich isotopes^139–146Ba and¹⁴⁸Ba. Nuclear moments and mean square charge radii of these isotopes have been recalculated. The isotope shift of the isotope¹⁴⁸Ba (T_1/2=0.64 s) could be studied for the first time, yieldingδ〈r²〉^138,148=1.245(3) fm².     

Hyperfine splitting and isotope shift in the optical transition of Eu isotopes and electromagnetic moments of Eu

The laser-induced resonance fluorescence in an atomic beam was used in order to measure the hyperfine splitting of the 4f ⁷ 6s ² and 4f^{7 6s6p} levels in ^151,153,155Eu isotopes. The hfs constants A and B of the unstable ¹⁵⁵Eu were determined for the first time: MHz, MHz and MHz. With these data and after corrections for second-order hyperfine structure perturbations the nuclear moments of ¹⁵⁵Eu were deduced: n.m. and b. In addition new and more precise values of the hfs constants of the excited state for the stable ^151,153Eu were obtained. They are as follows: MHz, MHz and MHz, MHz. The hyperfine anomalies % and % were extracted from the corrected hfs constants. Received 28 July 1999 and Received in final form 14 January 2000     

Correlation measurements on regular and irregular ionization waves in neon

The evolution from regular to fully irregular motion of the s variety of an ionization wave in neon is studied by space correlation measurements. The correlation functions clearly indicate the onset of strongly nonlinear interaction (by a change in the decay constant of correlation function) in the region of coherent wave motion, the transition to irregular wave motion (short distance correlation only) and the stochastic character of fully developed irregular wave motion (correlation only over a few wavelengths and a few periods).     

Electric monopole transitions and isotope shift of nuclear radii of even Sm isotopes in the interacting boson model

The interacting boson model has been used to calculate the isotope shift in^146–154Sm isotopes. Fitted model parameters have been used for calculation of the monopole strength parameters (EO) and the branching ratios X(EO/E2) for^150–154Sm. Consideration of the effective proton boson number as it reflects the Z=64 subshell closure, is shown to be insignificant in the present calculation.     

A re-evaluation of isotope shift constants

The field isotope shift constantC _unif for a uniform nuclear charge distribution has been re-evaluated fors-electrons for elements with 10≦Z≦ 95. A table is given which permitsC _unif to be found for any isotope pair.     

Laser spectroscopy and mass measurements on alkali isotopes

Isotope shifts, spins, hyperfine structures and masses have been measured for the series of the alkali isotopes including the nuclei far from stability. The method of laser spectroscopy and its combinations with rf excitation are described. Some results are discussed, namely the first observation of the red doublet D₁-D₂ of francium, and the study of shell effects and changes of shape with mass and δ〈r ²〉 measurements for Rb and Na isotopes.     

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     

Emission anomalous optical magnetic resonances in a mixture of even neon isotopes

Unusual resonances have been detected in the dependence of the discharge glow in neon on the longitudinal magnetic field. The resonances appear in fairly high magnetic fields and are observed only at low gas pressures and exclusively in a mixture of ²⁰Ne and ²²Ne isotopes. This phenomenon is an evidence of collective resonant radiation processes involving atoms of different neon isotopes.