Half-lives and delayed neutron emission probabilities of short-lived Rb and Cs precursors

Half-lives and delayed-neutron emission probabilities (P _n ) of short-lived Rb and Cs precursors in the mass chains 94–98 and 143–147 were measured. Sources of isotope separated nuclides were obtained from the on-line mass-separator OSTIS installed at the Grenoble high-flux reactor. A newP _n -value of (25.4±3.2)% is given for the (214±30) ms¹⁴⁷Cs; theP _n -values of nine alkali precursor nuclides were redetermined: (2,730±20) ms⁹⁴Rb with (9.7±0.5)%, (377 ±6)ms⁹⁵Rb with (8.6±0.5)%, (197±5)ms⁹⁶Rb with (12.5±0.9)%, (171±4) ms⁹⁷Rb with (25.2±1.8)%, (114±13)ms⁹⁸Rb with (18.4±2.9)%, (1,765±30)ms¹⁴³Cs with (1.74 ±0.12)%, (1,000±10)ms¹⁴⁴Cs with (2.95±0.25)%, (616±20) ms¹⁴⁵Cs with (12.2±0.9)%, (325±10)ms¹⁴⁶Cs with (13.2±0.8)%. The results are compared with the existing data, and theP _n -values are discussed within some simple model predictions.     

Polarization spectroscopy of Rb and Cs

Theoretical calculation of ⁸⁵Rb and ¹³³Cs D₁ signals in polarization spectroscopy is presented by using the method of velocity-selective optical pumping in a four-level system. Since good agreement between theory and experiment has been found in Na D₁ polarized signals, the theoretical calculation can be also applied to Rb and Cs D₁ lines. Rb and Cs atoms have higher total angular momentum F in the hyperfine structures than Na atom and then the calculation is more complicated. The relative signal intensities in polarization spectroscopy are compared with those in saturation spectroscopy.     

〈S0〉Cs and 〈S0〉Rb relaxation in the presence of buffer gas and the spin exchange between Cs and Rb

〈S⁰〉_Rb and 〈S⁰〉_Cs relaxation is studied in the presence of buffer gas and spin exchange between Cs and Rb. Spin exchange collisions are found to equalize the relaxation rates of Rb and Cs polarization. This result is completely confirmed experimentally for the relaxation of the first diffusion mode.     

Thermodynamics of melting of lithium,potassium and rubidium at high pressures

Volume measurements of liquid and solid Li, K and Rb in the vicinity of their melting curves have been carried out using a piston piezometer method. From the experimental results the volume, entropy and internal energy changes upon melting of the metals are calculated. The obtained data are analyzed along with the results for Na and Cs.It is stated that the anomalies in the melting curves of K, Rb and Cs are most probably connected with a s-d electron transition.     

Search for superdense nuclei of Rb and Cs among the products of 8 GeV proton interactions with Ta

Experimental searches for β-active superdense nuclei of Rb and Cs among the products of 8 GeV proton interactions with Ta are described. The method of selective off-line mass-separation with scanning of the β-activity distribution on the collector was used. According to π-condensation theory, the long-lived anomalous nuclei are expected to be more neutron-deficient than the usual ones. Moreover, their mass numbers may be significantly nonintegral measured on the normal mass scale, because of unusual binding energy. These predictions guided the present search. No anomalous nuclei were found. The upper limit for Rb nuclei in the range 69 ? A ? 78 is 10^?5 with respect to the yield for ⁸¹Rb; for Cs in the range 112 ? A ? 122 the limit is (5–10) × 10^?6 of the yield for ¹²⁷Cs. These estimations are based on the assumption that the half-life of superdense nuclei equals 5 h.     

Beta-decay energies and masses of short-lived isotopes of rubidium,caesium, francium,and radium

Total decay energies have been measured for a number of neutron-deficient Rb and Cs isotopes, as well as for some neutron-rich isotopes of Fr and Ra. Mass separated sources were produced at the ISOLDE on-line separator at CERN. By applying two differentβ-γ coincidence methods,Q values or their lower limits were determined for^76–78Rb,⁸⁰Rb,^121–124Cs,²²²Fr,^224–226Fr,²²⁹Ra-²²⁹Ac. For many of these nuclei, the atomic mass excesses could be derived, allowing the comparison of masses of far unstable nuclei with predictions from mass formulae. The odd-odd nuclei⁷⁶Rb and⁷⁸Rb appear to be 1?1 1/2 MeV more strongly bound than expected from the systematics.     

Site selectivities of alkali ions in CsRb2C60 and Cs2RbC60 superconductors

The temperature-dependent site selectivities of Cs and Rb ions in CsRb₂C₆₀ and Cs₂RbC₆₀ superconductors are computed using the free energy obtained from the configuration entropy and the total energy calculated using the ab initio pseudopotential density-functional theory. It is found that in CsRb₂C₆₀ the smaller Rb ions can occupy a considerable number of large octahedral interstitial sites at high temperatures, however, the transition to random occupation never takes place. For Cs₂RbC₆₀ the Cs occupancy of the large octahedral interstitial sites is almost always 100%, and, interestingly, the two tetrahedral interstitial sites are randomly occupied by Cs and Rb ions even at very low temperatures.     

Two-component exciton model

We have measured the broadening, and in one case also the shift, of alkalinS andnD Rydberg levels by alkali perturbers (Cs by Cs, Rb by Cs and K, and K by Rb) applying the Doppler-free two-photon technique and thermionic detection. Taking into account recent experimental data for the self-broadening of K and Rb Rydberg levels we found that for low principal quantum numbersn the broadening data of the levels are in agreement within the limits of experimental uncertainty in the pure and mixed cases. For highn we could establish that the broadening of the levels is governed by the perturber-valence electron and the perturber-ion core interaction. With increasingn the broadening rates are only dependent on the sort of perturber. As reported recently for Rb-Rb and K-K, oscillations in the broadening data as a function ofn were also observed for Cs-Cs and in the mixed vapours. Our results do not support recent theories which describe the oscillations in terms of resonances in the scattering of the quasifree valence electron on the perturber atom. In a classical absorption experiment oscillations in the self-broadening and shift of the Cs principal series lines discovered by Mazing and Serapinas were found to be due to satellite structures which are merged in non-Lorentzian line wings.     

New limits on the drift of fundamental constants from laboratory measurements

We have remeasured the absolute 1S-2S transition frequency nu(H) in atomic hydrogen. A comparison with the result of the previous measurement performed in 1999 sets a limit of (-29+/-57) Hz for the drift of nu(H) with respect to the ground state hyperfine splitting nu(Cs) in 133Cs. Combining this result with the recently published optical transition frequency in 199Hg+ against nu(Cs) and a microwave 87Rb and 133Cs clock comparison, we deduce separate limits on alpha/alpha=(-0.9+/-2.9) x 10(-15) yr(-1) and the fractional time variation of the ratio of Rb and Cs nuclear magnetic moments mu(Rb)/mu(Cs) equal to (-0.5+/-1.7) x 10(-15) yr(-1). The latter provides information on the temporal behavior of the constant of strong interaction.     

A high phase-space density mixture of 87Rb and 133Cs: towards ultracold heteronuclear molecules

We report the production of a high phase-space density mixture of ⁸⁷Rb and ¹³³Cs atoms in a levitated crossed optical dipole trap as the first step towards the creation of ultracold RbCs molecules via magneto-association. We present a simple and robust experimental setup designed for the sympathetic cooling of ¹³³Cs via interspecies elastic collisions with ⁸⁷Rb. Working with the |F = 1,m _F = +1〉 and the |3, +3〉 states of ⁸⁷Rb and ¹³³Cs respectively, we measure a high interspecies three-body inelastic collision rate ～10^?25?10^?26 cm⁶ ? s^?1 which hinders the sympathetic cooling. Nevertheless by careful tailoring of the evaporation we can produce phase-space densities near quantum degeneracy for both species simultaneously. In addition we report the observation of an interspecies Feshbach resonance at 181.7(5) G and demonstrate the creation of Cs₂ molecules via magneto-association on the 4(g)4 resonance at 19.8 G. These results represent important steps towards the creation of ultracold RbCs molecules in our apparatus.     

Selective reflection of laser radiation from submicron layers of Rb and Cs atomic vapors: Applications in atomic spectroscopy

We studied selective reflection (SR) of laser radiation from a window of a nanocell with thickness L ~ λ_1,2/2 filled with Rb and Cs atoms, where λ₁ = 780 nm and λ₂ = 852 nm are the wavelengths resonant with the D₂ laser lines for Rb and Cs, respectively. It is demonstrated that the negative derivative of the SR signal profile for L > λ/2 changes to the positive one for L < λ/2. It is shown that the real-time formation of the SR signal profile derivative (SRD) with the spectral width 30–40 MHz and located at the atomic transition is, in particular, a convenient frequency marker of D₂ transitions in Rb and Cs. The amplitudes of SRD signals are proportional to the atomic transition probabilities. A comparison with the known saturated absorption (SA) method demonstrated a number of advantages, such as the absence of cross-over resonances in the SRD spectrum, the simplicity of realization, a low required power, etc. An SRD frequency marker also operates in the presence of the Ne buffer gas at a pressure of 6 Torr, which allowed us to determine the Ne–Rb collisional broadening, whereas the SA method is already inapplicable at buffer gas pressures above 0.1 Torr. The realization simplicity makes the SRD method a convenient tool for atomic spectroscopy. Our theoretical model well describes the SRD signal.     

The far-wing broadening of the Na D lines by K,Rb and Cs and the electrostatic interaction potentials of the NaK,NaRb and NaCs molecules

The far wings of the NaD lines broadened by K, Rb and Cs have been measured in absorption by scanning a single-mode dye laser across the lines and detecting the flourescence signal. The relative absorption coefficients for the NaRb and NaCs are normalized using the impact widths recently measured by Kamke et al. The found red asymmetries of the lines are surprising results when only the theoretical van der Waals interactions are taken into account. It is demonstrated that the addition of dipole-quadrupole forces is necessary to explain the experimental findings. Using the extended electrostatic interaction potentials the theoretical impact widths of the NaD lines by Rb were found to be in agreement with the experimental data of Kamke et al.     

NMR in Li2 M 3Al(MoO4)4 triple molybdates (M = Rb,Cs)

Nuclear magnetic resonance (magic angle spinning) spectra of ⁷Li, ²⁷Al, ⁸⁷Rb, and ¹³³Cs nuclei are measured in Li₂ M ₃Al(MoO₄)₄ triple molybdates (M = Rb, Cs) for the first time. Analysis of the nuclear magnetic resonance spectra reveal considerable asymmetry in the distribution of the electric charge throughout the crystal lattices of the compounds.     

Influence of Rb,Cs, and Ba on the superconductivity of magnesium diboride

Magnesium diboride has been thermally treated in the presence of Rb, Cs, and Ba. The magnetic susceptibility shows the possible onsets of superconductivity in the resulting samples at 52 K (Rb), 58 K (Cs), and 45 K (Ba). Room-temperature ¹¹B NMR indicates the cubic symmetry of the electric field gradient at the boron site for the samples reacted with Rb and Cs, in contrast to the axial symmetry in the initial MgB₂ and in the sample treated with Ba. The text was submitted by the authors in English.     

Estimates of the bound-state QED contributions to the g-factor of valence ns electrons in alkali metal atoms

The bound-state QED corrections to g-factors are partly calculated and partly estimated for the ns valence electrons in the atoms K, Rb, Cs, Ba⁺ and Fr. It is shown that these corrections should be taken into account in the comparison with experimental data.     

Beta-decay energies and nuclear masses of very neutron-rich Rb and Cs isotopes

Theβ-endpoint energies of very neutron-rich Rb and Cs isotopes with mass numbers 94≦A≦98 and 142≦A≦146, respectively, have been measured with a plastic scintillatorβ-telescope at the on-line mass separator OSTIS. From these,Q _β-values and mass excesses are calculated and compared with the results obtained in direct mass determinations.     

Magnetic-resonance-frequency shifts in spin-exchange collisions of Rb and Cs alkali-metal atoms

On the basis of data on spin-exchange complex cross sections in the Rb–Rb and Cs–Rb systems, the magnetic-resonance-frequency shifts of rubidium atoms upon collisions in a mixture of Cs–Rb alkalimetal atoms are calculated. The results obtained are compared with the experimental data and the previous theoretical data.     

Inner core neutral atom binding energies — Comparison of relaxed-orbital theory with experiment

Neutral atom binding energies from relaxed-orbital relativistic Hartree-Fock-Slater calculations are compared with empirical values for Na, K, Rb, Cs, An and Cd atoms. The method is precise (within ～ 1 eV) for the highest l for a given n, but there are errors of several eV for s levels other than 1s.     

An equation of state for alkali metals

Semi-empirical equations of state based on Lindemann's law have been developed to determine the pressure (P) dependence of the melting temperature (T_m) of Li, K, Rb and Cs. The basic inputs are Grüneisen parameter and the bulk modulus. T_m–P variations exhibit maximum melting temperature with concave downwards. The maximum in T_m for Cs is found to occur at pressure of 2.2 GPa whereas for Li, K and Rb it falls in the range of 7–9.5 GPa. The predicted values of T_m as a function of pressure, based on the present empirical relation, fit quite well with the available experimental data. The empirical relation can also be used to extrapolate T_m at higher pressure from the values available at lower pressures.     

Bose-Einstein condensation of 87Rb in a levitated crossed dipole trap

We report an apparatus and method capable of producing Bose-Einstein condensates (BECs) of ～1 × 10^{6 87}Rb atoms, and ultimately designed for sympathetic cooling of ¹³³Cs and the creation of ultracold RbCs molecules. The method combines several elements: (i) the large recapture of a magnetic quadrupole trap from a magneto-optical trap; (ii) efficient forced RF evaporation in such a magnetic trap; (iii) the gain in phase-space density obtained when loading the magnetically trapped atoms into a far red-detuned optical dipole trap, and (iv) efficient evaporation to BEC within the dipole trap. We demonstrate that the system is capable of sympathetically cooling the |F = 1, m _F = ?1〉 and |1,0? sublevels with |1, +1〉 atoms. Finally we discuss the applicability of the method to sympathetic cooling of ¹³³Cs with ⁸⁷Rb.