〈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.     

Spektroskopische Untersuchung unelastischer Stöße zwischen Ionen oder metastabilen Atomen der Edelgase und Alkalimetallatomen bei thermischen Stoßenergien

The present work deals with the spectroscopic investigation of Penning ionization and nonresonant charge exchange due to thermal-energy collisions of metastable atoms or ions of the inert gases He, Ne with atoms of alkali metals K, Rb, Cs in a low temperature plasma of the corresponding binary mixtures. The rate constants of these reactions and partial rate constants of exciting several alkali metal ion levels were determined by the kinetics of the decay of ionized and excited particles in the afterglow of a pulsed discharge. Measured Penning and charge exchange constants are in order of 10^10-9 cm³ sec^?1. Partial Penning constants in the He? Cs system exhibit a small dependence of the energy defect of reaction, whereby an important part of collisions results in excited Cs⁺-states. On the contrary, energy transfer by charge exchange in He? Rb, Cs systems distinguishes by a significant energy defect dependence. Charge exchange from He⁺ to Rb₀ leads above all to He(2³S₁)-atoms and normal Rb⁺-ions. It follows from the metal ion spectrums, that Penning ionization and charge exchange of the investigated systems under utilized conditions represent as processes of selective excitation of alkali metal ions in afterglow and stationary discharge.     

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.     

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.     

Collisions of alkali K and Rb atoms in ground state: Modification of interaction potentials

The interaction of alkali K and Rb atoms that reside in the ground state is considered in the range of collision energies E = 10⁻⁴ to 10⁻² au. The singlet (X ¹Σ⁺) and triplet (a ³Σ⁺) interaction potentials available in the literature are analyzed and modified. For the KRb dimer in the range of interatomic distances 15–21a ₀, we chose analytical representations of the singlet and triplet potentials that more accurately describe the interaction of alkali Rb and K atoms in the ground state. Complex cross sections of the spin exchange are calculated for the first time that permit one to calculate the processes of polarization transfer and relaxation times, as well as shifts in the magnetic resonance frequencies caused by K-Rb spin exchange collisions.     

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.     

MEASUREMENTS OF RELAXATION OF SPIN POLARIZED 129Xe NUCLEI IN HIGH MAGNETIC FIELDS

We observed the NMR signal of low-pressure gas ¹²⁹Xe by laser enhanced method on an MSL-400 NMR spectrometer and measured nuclear spin relaxations of ¹²⁹Xe gas at various temperatures. The relaxation rate constant of ¹²⁹Xe-¹³³Cs spin exchange was obtained as (6.8±0.5)×10^-16cm^-3s^-1.     

Manipulation of ultracold atomic mixtures using microwave techniques

We used microwave radiation to evaporatively cool a mixture of of ¹³³Cs and ⁸⁷Rb atoms in a magnetic trap. A mixture composed of an equal number (around 10⁴) of Rb and Cs atoms in their doubly polarized states at ultracold temperatures was prepared. We also used microwaves to selectively evaporate atoms in different Zeeman states.     

Magnetic shielding studies on the alkali molecules Na2 and Cs2 by NMR

NMR in the alkali molecules Na₂ and Cs₂ is performed by the atom-molecule exchange optical pumping method. The shielding differences σ(Na)?σ(Na₂)=(29±16)·10^?6 and σ(Cs)?σ(Cs₂)=(221±12)·10^?6 are obtained. The investigation of the contribution of the valence electron to the magnetic shielding is supported by a NMR experiment in free Cs⁺ ions, which yields the shielding difference σ(Cs)?σ(Cs⁺)=(14±12)·10^?6. These measurements allow an estimation of the spin rotation interaction constant in these molecules.     

Phase transition and relaxation processes by 87Rb and 39K nuclear magnetic measurements of RbKSO4 single crystals

⁸⁷Rb and ³⁹K nuclear magnetic resonance (NMR) spectra of RbKSO₄ single crystals were measured at room temperature. ⁸⁷Rb central line has the angular dependences of second-order quadrupolar shifts. From these results, the quadrupole coupling constant and the asymmetry parameter were determined at room temperature. In addition, the spin–lattice relaxation rate, 1/T₁, and the spin–spin relaxation rate, 1/T₂, were measured as a function of temperature. The values of 1/T₁ for the ⁸⁷Rb and ³⁹K nuclei were found to increase with increasing temperature, and 1/T₁ was determined to be proportional to Tⁿ. Therefore, for the ⁸⁷Rb and ³⁹K nuclei, Raman processes with n=2 are more significantly in nuclear quadrupole relaxation than direct processes.     

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.     

Trapping radioactive atoms for basic and applied research

We report on the trapping of radioactive atoms for a variety of nuclear, atomic, and applied physics investigations. To date we have trapped 5 different radioisotopes of rubidium and cesium (^82–84Rb+^135,137Cs) using a magneto-optical trap (MOT) coupled to a mass separator. By optimizing the efficiency of this system, we have been able to trap as many as 6 million radioactive atoms and detect as few as 100. This technology is being applied in three different areas: (1) the parity-violating, β-decay asymmetry measurement of polarized ⁸²Rb; (2) the study of ultracold fermionic ⁸⁴Rb atoms; and (3) the use of MOTs for the ultrasensitive detection of selected radioactive species. Although all of these projects are in a formative stage of development, we highlight the progress that we have made in: (1) the trapping of ⁸²Rb atoms in double MOT system; (2) the hyperfine structure measurement of the 5P_1/2 and 5P_3/2 levels in ⁸²Rb; (3) the simultaneous trapping of ⁸⁴Rb and ⁸⁷Rb in overlapping MOTs; and (4) the first trapping and isotopic ratio measurement of ¹³⁵Cs and ¹³⁷Cs in a MOT. This revised version was published online in August 2006 with corrections to the Cover Date.     

Spin exchange polarization and hfs anomaly measurement of β-active37K

Rf-spectroscopic measurements in the atomic ground state of the 1.2 sec-isotope³⁷K yielded independent values of magnetic moment μ _I (³⁷K)=0.20320 (6) nm (diamagnetically corrected), hfs separation ΔW(³⁷K)=240.2672 (7) MHz and the resulting hfs anomaly³⁷Δ³⁹=(0.249±0.035) · 10^?2. The³⁷K was polarized by spin exchange scattering with optically pumped⁸⁷Rb; as a detector for rf transitions the asymmetry of the β-decay of the polarized³⁷K nuclei was used. A detailed analysis of the spin exchange mechanism under the conditions of experiments of this type was performed. This led to an explanation for the observed strong enhancement of the resonance signal heights by the spin bath. Furthermore the dependence of the nuclear polarization and relaxation time constants on the strength of the hfs coupling could be demonstrated.     

Half-lives of the new isotopes100Rb,100Sr,148Cs and of99Rb,99Sr and147Cs

An improvement of the ion source of the online fission product separator OSTIS allowed us to identify the new isotopes¹⁰⁰Rb(50±10 msec),¹⁰⁰Sr (170±80 msec) and¹⁴⁸Cs(130±40 msec). Half-lives for⁹⁹Rb(59±4 msec),⁹⁹Sr(290±40 msec) and¹⁴⁷Cs(235±10 msec) were redetermined. All values were obtained by following the activity build-up and decay with β-multiscaling and γ-multispectra measurements.     

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.     

Frequency-selective laser optical pumping and spin exchange of cesium with129Xe and131Xe in a high magnetic field

We report the experimental results of frequency-selective laser optical pumping and spin exchange of Cs with¹²⁹Xe and¹³¹Xe in a high magnetic field of 11.74 T. Our results show that hyperpolarized¹²⁹Xe and¹³¹Xe nuclear magnetic resonance (NMR) signals exhibit alternating phases when the laser frequency for pumping the cesium atoms is changed, which is explained on the basis of the high-field optical pumping of Cs. We obtain about 3% polarization of the¹²⁹Xe. The electron-spin polarization of the Cs atoms has been measured to be about 22% with a simple NMR method.     

Some effects of inhomogeneous strain on surface properties of metals: I. Flat surface

Jelium model calculations using the many electron formalism and a parameterized charge density distribution have been used to evaluate the change in surface energy, barrier height and work function due to the presence of a tensile and compressive strain gradient at the surface of Cs, Rb, K and Na. The method is useful for short range strain fields (? 4–5 atom spacings), but not for larger fields. The surface energy change due to inhomogeneous strain is almost twice as large as that due to homogeneous strain. The work function changes due to inhomogeneous strain are ~10–10² times larger than those due to homogeneous strains. The results are of considerable importance to general fracture and stress corrosion cracking studies.     

Relaxation rates of 69Ga and 71Ga nuclei in aqueous solutions

Line widths in the ⁶Li, ⁷Li, ²³Na, ³⁹K, ⁸⁵Rb, ⁸⁷Rb and ¹³³Cs N.M.R. spectra of solutions of the alkali salts of biphenyl and fluorenone are reported as a function of solvent and temperature. From a numerical analysis of the room temperature data the contribution of the various relaxation mechanisms to the line widths are established. It is shown that the results are consistent with the observed solvent and temperature dependence of the line widths. Values of the electron spin correlation time are obtained and a value of 1·6 ± 0·4 Å is found for the ‘Van der Waals radius’ of the biphenyl anion. Line width expressions for the static and the dynamic ion pair model are presented. It is demonstrated that the static ion pair model applies to solutions of caesium biphenylide. Semi-empirical rules are presented concerning the importance of various relaxation mechanisms for the different alkali nuclei in the type of solution studied here.     

Raman Spectrum of the Fluorination Products of RbC1

Abstract

Compounds with high fluorinating capacity are obtained when rubidium and cesium chlorides are fluorinated in a stream of elemental fluorine. Best results are obtained when the, temperature is kept in the range of 140–170°C. These products were first assumed to be polyfluorides, MF₃, of Rb and Cs ¹. It was later assumed by various researchers ² that the products are really tetrafluorohalates of Rb and Cs, formulated as MC1F₄. One of the authors was himself involved in the problem of trying to establish the structure of these products. It is, however, a very difficult problem since pure products giving constant analytical results were not obtained. During the fluorination process, which is an exothermic one, enough heat is evolved to melt the reaction medium and the temperature rises above that needed to decompose the products. It is therefore impossible to obtain reliable analytical data, the products being a mixture of regular fluorides, MF, and the active, fluorinating, ones. No final proof has therefore been found for the C1F^? ₄ structure.