Optical pumping of ions in buffer gases

Transient signals measured with a pulsed rf-optical pumping method are used to determine longitudinal relaxation rates for Sr⁺ ions (even isotopes) in noble gas buffers. Depolarization cross sections of the electronic spin in the Sr⁺5² S _1/2 ground state for binary collisions with rare gas atoms are deduced. The results for σ(Sr⁺5² S _1/2) in Ų are (at temperatures between 374 and 449 °K): 2·10^?5(He),4·10^?5(Ne), 5.7·10^?3(Ar), 1.8·10^?2(Kr), and 4.0·10^?2(Xe). These cross sections for the Sr⁺ ion are about two to three orders of magnitude larger than the corresponding ones for the isoelectronic neutral Rb atom. The large increase of the Sr⁺ relaxation rates is explained with the relaxation mechanism of spin-orbit coupling, taking into account two “indirect” effects of the ionic charge: the increase in the gas kinetic cross sections and the more intimate collisions of the Sr⁺ ion with the noble gas atoms. The depolarization is shown to be predominantly due to short-range interactions. A contribution to the relaxation of the Sr⁺ ion from Sr⁺-noble gas molecule formation, induced by three-body or resonant two-body collisions, could not be established for applied pressuresp between 1.5 and 15 Torr of Ar, Kr, and Xe.     

Polarization effects in ionizing thermal energy collisions of laser-excited Ne(3p 3 D 3) atoms with Ar atoms

Using transverse and longitudinal excitation of a collimated metastable Ne(3s ³ P _2.0) beam with average velocities of 500, 800, and 1,200 m/s by means of a single mode dye laser on the²⁰Ne(3s ³ P ₂→3p ³ D ₃) transition, we have investigated ionizing collisions of polarized Ne(3s ³ P ₂) and Ne(3p ³ D ₃) atoms with Ar atoms. The product electrons were energy analyzed with high resolution (9–25 meV). The resulting Ne(3p ³ D ₃) electron spectra exhibit a strong dependence on the three types of laser polarization (π _∥,π_⊥, σ_?), chosen to prepare the excited atoms. In contrast, the Ne(3s ³ P ₂) spectra are only weakly dependent on polarization. Detailed model calculations have been carried out for the Ne(3p)+Ar cross sections, using computed excited-state potential curves, semi-empirical ionic potentials, and local autoionization width functions. A semiclassical closecoupling method is applied to describe the evolution of the polarized collision system in the coupled entrance channels. It is found that a single autoionization widthΓ(R) is not sufficient to describe the measured polarization effects properly. The dependence ofΓ on the initial and final state is expressed in terms of few reduced electronic transition matrix elements, which are determined by comparison of measured and calculated total cross sections and Ar⁺(² P _3/2)/Ar⁺(² P _1/2) branching ratios for ionizing collisions of the various Ne(3pJ=1,2,3) multiplet states with Ar. The matrix elements corresponding to Ar(3pσ)→Ne(2pσ) electron transfer during autoionization are found to dominate, but Ar(3pπ)→Ne(2pπ) transfer has also to be included. The resulting calculated electron spectra reproduce the measured polarization effects in a semi-quantitative way.     

Multiple ionization of neon 2s- and 2p-electrons induced by ion atom collisions

Absolute cross sections for production of the 1s ²2s2p ⁵ and 1s ²2s ⁰2p ⁶ configurations of neon in collisions of H⁺, He⁺, and Ne⁺ with Ne and He have been measured by observation of radiative transitions in the spectral range of the vacuum ultraviolet for energies between 50 keV and 1 MeV. Projectile and target emission have been separated. The dependence of the cross sections upon impact velocity is discussed and compared with theoretical calculations. The relative population of the¹ P ₁ and³ P _{2, 1, 0} and the³ P _{2, 1, 0} fine structure levels of the 1s ²2s2p ⁵ configuration is measured as function of impact velocity for the different projectile target combinations.     

Relaxationserscheinungen im 63 P 2-Zustand des Quecksilber-Isotops199Hg bei Stößen mit Quecksilberatomen im Grundzustand

The decay ofrf resonance signals (Δm _F =± 1, ΔF=0) in the hfs-states (F=3/2, 5/2) of the 6³ P ₂-state of¹⁹⁹Hg has been observed by means of a sampling method. By comparing the relaxation times to those of the even isotopes, the cross section σ₂(F) for the destruction of an alignment in the hfs-states by collisions with ground state Hg-atoms could be measured. The following ratios were obtained: σ₂(F=3/2)/σ₂=1.04±0.06 and σ₂(F=5/2)/σ₂=0.90± 0.03. The cross section σ₂ for the even isotopes was found to be (2.620±0.265) 10^?14cm². Assuming total decoupling of nuclear spinI and electronic angular momentumJ during the collision, the cross sections for the destruction of an orientation (σ₁) and an “octupolarisation” (σ₃) could be calculated. For the even isotopes the following ratios were derived: σ₁/σ₂=0.76 ± 0.07 and σ₃/σ₂=1.08 ± 0.09.     

K-vacancy production by 3.6-, 4.75-, and 5.9-MeV/amu238U Ions

Projectile (Z ₁) and target (Z ₂)K-vacancy production cross sections induced by 3.6-, 4.75-, and 5.9-MeV/amu²³⁸U ions in selected targets between C and U are reported. The cross sections are discussed within the context of the molecular model of inner-shell vacancy production in heavy-ion-atom collisions. The measured 1sσ and 2pσ excitation cross sections are compared with semiempirical formulas, and with the perturbed-stationary-states calculations of Betz et al. The dependence of these cross sections onZ _u =Z₁+Z ₂ agrees well with the Betz calculations. However, the measured cross sections are factors of 2 to 4 (1sσ) and 4 to 5 (2pσ) larger than the theoretical values.     

Level-crossing-Experiment am 6s6p 3 P 1-Term im Ba I-Spektrum

The hfs-splitting of the stable odd Ba-isotopes Ba¹³⁵ and Ba¹³⁷ (I=3/2) in the 6s6p ³ P ₁-state was investigated by level crossing techniques. For both isotopes two crossings between Zeeman-sublevels withδm _F=2 were detected by resonance scattering of the 7911 å-intercombination line using a Ba-atomic beam. From the experimental results ratios of zero field hfs-constants and theg _J-value of the³ P ₁-state were calculated including second order corrections. The results may be compared with double resonance measurements in zero magnetic field.     

Measurements ofK-shell ionization with132Xe and208Pb projectiles in the energy range of 1.4–5.9 MeV/u

Projectile and targetK-shell ionization cross sections induced by 3.6-, 4.7-, and 5.9 MeV/u¹³²Xe ions and 1.4-, 3.6-, 4.7-, and 5.9 MeV/u²⁰⁸Pb ions from the UNILAC in thin solid targets between C and U are measured. The cross sections are discussed in terms of the molecular model of innershell vacancy production in heavy ion-atom collisions. The sharing of 2p _1/2σ vacancies between theK shells of the two collision partners in these very heavy ion-atom collisions is found to deviate from the Meyerhof-Demkov formula forR≦10^?2. The measured ionization cross sections are compared with theoretical calculations for 1sσ and 2p _1/2σ excitation cross sections. AZ _UA=Z₁+Z ₂ dependence is found independent ofZ ₁/Z ₂. Outer-shell vacancy configurations measured in these close encounters are reported.     

K +-meson production inpBe interactions atT p=2.9 GeV

The production ofK ⁺ andπ ⁺ mesons and protons inpBe collisions atT _p=2.9 GeV has been studied at the ITEP proton synchrotron. Ejectiles with a momentum ofp=545 MeV/c were observed under an emission angle ?=17°. The detectors which have been developed for the identification of kaons out of a six orders of magnitude more intense background of pions and protons are described. A cross-section ratio d²σ _K ⁺/dΩdp: d² σ _p /dΩdp: d²σ _p /dΩdp of (1±0.34):(85±1):(31±1) has been measured. Normalization with existing pion data yields an invariant differential cross sectionE·d³σ _K ⁺/d³ p=(3.1±1.2) mbGeV^?2c³sr^?1 and a total cross section of σ_tot(pBe)=(3.7±1.5) mb. These cross sections are compared with existing data and theoretical predictions. TheA dependence ofK ⁺ production in the few-GeV range is analyzed.     

Spin relaxation of the8 S 7/2 ground state of europium in noble gases

Spin relaxation of the 4f ⁷ 6s ^{2 8} S _7/2 ground state of the Eu atom in noble gases was investigated by the direct, continuous optical pumping method. Transient signals could be observed by pulsed saturation of rf Zeeman transitions within theF= 6 hfs level of the stable Eu isotopes. The time constant of the transient signals can be related to the electronic spin depolarization cross section for Eu-noble gas collisions, yielding noble gas He Ne Ar Kr Xe σ₁in 10^?20 cm² 0.99(10) 5.1(5) 15(1.5) 43(4) 97(10) These cross sections exceed those measured forS-states of alkalies by three orders of magnitude. They can be explained by perturbations of theS-ground state configuration of Eu due to the admixture of excited state non-spherical wave functions.     

Theoretical study of photoionization of the isoelectronic sequence Rb<Superscript>+</Superscript>, Sr<Superscript>2+</Superscript>, and Y<Superscript>3+</Superscript>

The photoionization cross sections for the 4p shell of ions of the Kr isoelectronic sequence Rb⁺, Sr²⁺, and Y³⁺ are calculated. The configuration interaction theory and the perturbation theory are used to describe the many-electron effects. The relativistic effects are taken into account in the Pauli-Fock approximation. The calculated resonance structure of photoionization cross sections for the 4p shell in the region below the 4s threshold associated with the autoionization of the 4s-np singly excited states and the 4p4p-nln′l′ doubly excited states reproduces the results of recent measurements of total photoabsorption cross sections for the Rb⁺, Sr²⁺, and Y³⁺ ions. It is found that, as the nuclear charge in the isoelectronic sequence increases, the ratio between the direct and correlation parts of amplitudes of the 4s-(n/?)p transition changes and, as the consequence, the minimum of the photoionization cross section of the 4s shell shifts from the continuous spectrum to the region of states of discrete spectrum. This accounts for the strong changes in the shape of the 4s-np resonances in the photoionization cross sections for the 4p shell of Rb⁺, Sr²⁺, and Y³⁺, as well as the distinction between the shapes of the 4s-6p _1/2 mirror resonance in the partial 4p _1/2 and 4p _3/2 photoionization cross sections for the Y³⁺ ion which do not suppress each other in the total photoionization cross section, as is the case for similar resonances in Rb⁺ and Sr²⁺.     

Optical detection of Yb+ trapped in an rf trap

The fluorescence from Yb⁺ ions trapped in an rf trap was detected by driving the²S_1/2−²P_1/2 transition at 369.52 nm with the radiation generated by sum-frequency mixing of diode-laser and argon-ion-laser radiation. The rf resonance absorption signal as well as the fluorescence signal, when the Yb⁺ ions were continuously irradiated by the resonant uv radiation, faded out with a decay time shorter than the storage time. This observation suggests that the Yb⁺ ions disappeared from the trap with the irradiation of the resonant uv radiation.     

Collisional depolarization and redistribution of laser radiation in near resonance with a2 P 3/2↔2 S 1/2 transition

We have investigated experimentally and theoretically the spectral distribution and collisional depolarization of laser light near resonant to the Na transition 3² S _1/2?3² P _3/2 scattered from a Na/Ar mixture in a cell (n _Na≈4.0×10¹⁰cm^?3,n _Ar≈1.0×10¹⁷cm^?3). In particular, at excitation intensity of ≈3mW/mm² and bandwidth of <10 MHz, intensityI _F and linear polarization degreeP _F of theD ₂-fluorescence component of the scattered spectrum have been measured as functions of the laser detuningΔλ _L from theD ₂-resonance within two regions: 1) ¦Δλ _L ¦-Doppler-width; 2) 20≧¦Δλ _L ¦/Δλ _D ≧1. Within the first region the influence of hyperfine splitting as well as pumping of the hyperfine and Zeeman sublevels of 3² S _1/2 was studied in detail. Using an overall, total collision cross section for depolarization of 3² P _3/2 state atoms, calculations on the basis of the theory of redistribution reproduce qualitatively, but in a consistent manner, the experimental functionsI _F(Δλ_L) andP _F (Δλ _L ). The possibility to derive differential cross sections fromP _F (Δλ_L) is discussed.     

Reliable cross sections of partial photoneutron reactions on 188,189Os isotopes free of neutron multiplicity sorting problems

Experimental data on the cross sections of partial photoneutron reactions, obtained for ^188,189Os isotopes using quasimonoenergetic annihilation photon beams and neutron multiplicity sorting method, are analyzed. Using special criteria (transition multiplicity functions F _i = σ(γ, in)/σ(γ, xn), the ratios of the cross section of the corresponding partial reaction to the total neutron yield reaction’s cross section σ(γ, xn) = σ(γ, 1n)+ 2σ(γ, 2n) + 3σ(γ, 3n) free of the problems associated with experimental neutron multiplicity sorting), it is demonstrated that the data contain significant systematic errors. New data are evaluated for cross sections of partial photoneutron reactions (γ, 1n), (γ, 2n), (γ, 3n) and total photoneutron reaction (γ, sn) for ^188,189Os isotopes within an experimental-theoretical approach proposed earlier. It is shown that the significant systematic errors in the experimental cross sections of partial reactions can be attributed to the ambiguity of the relation between the photoneutrons’ multiplicity and their kinetic energy.     

Screening effects in secondary electron production by equal velocity H+, H+2, He+, He++ions

Electron spectra produced by equal velocity (0.75 MeV/amu) H⁺, H⁺₂, He⁺ and He ⁺⁺ ions are shown. Screening effects are observed for He⁺ ions but not for H⁺₂. He⁺⁺ cross sections scale like Z² = 4 when compared to H⁺ cross sections.     

Analysis of inelastic scattering of3He on14C at 37.9 MeV

The differential cross sections of elastic and inelastic scattering of³He ions on the¹⁴C nucleus have been measured at an energy of 37.9 MeV. By fitting the shape of the measured angular distribution of the elastic scattering the parameters of the optical model have been found. These parameters have been used for the standard DWBA calculations of angular distributions corresponding to excitations of the¹⁴C levels 6.73(3^?), 7.01(2⁺) and 8.32(2⁺) MeV and for coupled channels calculations of the level 8.32(2⁺) MeV. The vibration parametersβ _L of the¹⁴C nucleus have been deduced.     

Charge states of atoms in the lattices of the high-temperature superconductors Tl2Ba2Ca n−1CunO2n+4 and Bi2Sr2Ca n−1CunO2n+4

To determine the charges of atoms in the lattices of the compounds Tl₂Ba₂Ca _n?1Cu_nO_2n+4 and Bi₂Sr₂Ca _n?1Cu_nO_2n+4 (n=1,2,3), the parameters of the electric field gradient tensor at the copper sites of the indicated lattices were found by emission Mössbauer spectroscopy on the isotopes ⁶¹Cu(⁶¹Ni) and ⁶⁷Cu(⁶⁷Zn), and a calculation of these parameters was performed in the point-charge approximation. A comparison of the resulting values and the published data on ⁶³Cu nuclear quadrupole resonance showed that agreement between the experimental and computed values of the parameters obtains for models in which the holes resulting from a reduction in the valence of some of the thallium (bismuth) atoms are localized predominantly at oxygen sites located in the same plane as the copper atoms (for the compounds Tl₂Ba₂Ca₂Cu₃O₁₀ and Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₀—at oxygen sites in the same plane as the Cu(2) atoms).     

Triple ionization of lithium-like ions by photon impact

Within the framework of sudden approximation, the non-relativistic cross sections for the triple ionization of Li-like ions caused by absorption and Compton scattering of high-energy photons are calculated. The ratios of the triple-to-single and triple-to-double ionization cross sections are obtained. For neutral lithium atom, our predictions for σ3+/σ⁺ and σ3+/σ2+ are compared both with available experimental and theoretical results.     

Inclusive φ-meson production in 93 and 63 GeV hadron interactions

The inclusive reactions h+p→φ+X, (h=π^±,,K^±,p^±), are studied for 0?x_F?0.3 and p⊥ ? 1 GeV at 93 and and 63 GeV incident momentum. Differential cross sections dσ/dp_⊥² anddσ/dx_F are presented and are compared with predictions of the naive parton model.     

Hyperfine density shifts of137Ba+ ions in noble gas buffers

Fractional hyperfine density shifts (fds) for¹³⁷Ba⁺ (I=3/2) ions are measured by means of direct optical pumping in noble gas buffers. The results for the fds (¹³⁷Ba⁺, 6s ² S _1/2) in units of 10^?9/Torr (0 ?C) (measured at temperatures between 375 and 395 K) are: + 7(7) (He), ?74(8) (Ne), ?825(80) (Ar), ?1 500(200) (Kr), and < ?1600 (Xe). These shifts for the¹³⁷Ba⁺ ion are considerably more negative than those for the isoelectronic¹³⁷Cs atom. It is shown that this difference can be explained by taking into account the additional charge induced interaction. The hyperfine splitting frequency of the unperturbed¹³⁷Ba⁺ 6s ² S _1/2 state is extrapolated tov ₀=8037741.6(6)kHz.     

Übertragung von Polarisation bei sensibilisierenden Stößen angeregter Natriumatome

The transfer of magnetic polarization from state 3p ² p _1/2 to state 3p ² p _3/2 sensitizing collisions of sodium atoms with noble gas atoms has been observed. Sodium atoms were excited by absorption ofD ₁σ⁺-quanta. When buffer gas was added to the sodium vapour, unequal amounts ofD ₂σ⁺ andD ₂σ^? quanta could be detected in the fluorescent light. The difference of the amounts turned out to be proportional to the polarization transferred. The measurement of this difference as a function of the buffer gas pressure provided a method of determining the cross-sections of the polarization transfer. Values of the cross-sections are 22, 24, 26, 20, 23 Ų for the buffer gases He, Ne, Ar, Kr, Xe, respectively. A preliminary investigation shows that the sign of the polarization transferred is reversed when the vapour is exposed to a strong magnetic field acting along the incident light beam.