Lebensdauer- und Hyperfeinstrukturmessungen an einigen angeregten Zuständen der Konfiguration 4d 9 5p im Pd I-Spektrum mit der Level-crossing-Methode

Lifetimes and hfs coupling constants of some excited states of the 4d ⁹ 5p configuration of Pd I have been determined in a level crossing experiment by observing the field dependence of the polarization of the fluorescence radiation in a magnetic field. From the halfwidths of the measured zero field level crossing signals one obtains the mean lifetimes of the following fine structure states:τ(³P ₁ ⁰ )=(7.46±0.32)nsec;τ(³ P ₂ ⁰ )=(6.9±0.76)nsecτ(³P ₁ ⁰ )=(4.99±0.35)nsec;τ(³ D ₁ ⁰ )=(4.89±0.40)nsecτ((³D ₃ ⁰ )=(6.99±0.49)nsec;τ(³ F ₄ ⁰ )=(7.09±0.46)nsec.Δm=2 crossing signals were detected in the³ P ₁ ⁰ ,³D ₃ ⁰ and³F ₄ ⁰ -states of the odd isotope¹⁰⁵Pd. A detailed analysis of the experimental curves yields the hfs coupling constantsA andB of these states:A(³P ₁ ⁰ )=?(133±2) Mc/sec;B(³ P ₁ ⁰ )=(140±30) Mc/secA(³D ₃ ⁰ )=?(120±10) Mc/sec;B(³ D ₃ ⁰ )=?(660±100) Mc/secA(³F ₄ ⁰ )=?(87±2) Mc/sec;B(³ F ₄ ⁰ )=?(330±30) Mc/sec. A theoretical calculation of the hfs constants is given on the basis of reduced matrix elements. Within the limit of the errors these values agree with the experimental ones. The nuclear electric quadrupole moment deduced from the measuredB values isQ (¹⁰⁵Pd)=(0.8±0.3)·10^?24 cm² (without corrections).     

Discharged generator of singlet oxygen for oxygen-iodine laser. Transport kinetics of O2(a 1δg) and O2(b 1σ g + ) molecules and O(3 P) atoms in Ar:O2 and He:O2 flows excited by a 13.56-MHz discharge

To understand and reveal the basic physical factors providing the possibility of scaling of a discharged singlet oxygen generator (DSOG) in an oxygen-iodine laser, the production, and transport kinetics of metastable O₂(a ¹δ_g) and O₂(b ¹σ _g ⁺ ) molecules, as well as O(³ P) atoms, were investigated in Ar:O₂ and He:O₂ gas flows excited by a 13.56-MHz discharge in a wide range of pressures (4–40 Torr) and oxygen percentages. It is shown that the densities and transport kinetics of O₂(a ¹δ_g), O₂(b ¹σ _g ⁺ ), and O(³ P) appear similar for oxygen mixtures with argon and helium in the same conditions independent of discharge mode. Compared to pure O₂, the dilution of oxygen with an inert gas allows higher energy inputs per an oxygen molecule to achieved, especially under conditions of the homogeneous discharge mode (α-mode), which gives a higher efficiency of O₂(a ¹δ_g) excitation in Ar:O₂ and He:O₂ mixtures. But the maximum attainable yield of singlet oxygen in Ar:O₂ and He:O₂ at fixed partial O₂ pressure is found to be comparable with the O₂(a ¹δ_g) yield in pure oxygen at the same pressure. The reason for this is the increased three-body deactivation of O₂(a ¹δ_g) by atomic oxygen in the mixtures because of the greater total pressure. The estimation of the rate constant of O₂(a ¹δ_g) three-body quenching by O(³ P) in Ar:O₂ and He:O₂ mixtures as (1.5 ± 0.5) × 10^?32 cm⁶/s was carried out from the analysis of transport kinetics of singlet and atomic oxygen in the discharge afterglow at high pressures exceeding ～10 Torr. A similar analysis for the lower pressures has revealed that losses both of metastable O₂(a ¹δ_g) and O₂(b ¹σ _g ⁺ ) molecules, and of O(³ P) atoms on the surface of the discharge tube, are determined by the density of each of the components. The obtained loss probabilities of O₂(a ¹δ_g), O₂(b ¹σ _g ⁺ ), and O(³ P) on the silica surface show that the surface loss probabilities of all the species can increase noticeably under the discharge exposure. Thus, the key parameters determining the maximal O₂(a ¹δ_g) yield in the DSOG are a homogeneous volumetric mode of the discharge, energy input per oxygen molecule in this mode, and a low rate of O₂(a ¹δ_g) quenching. Just three-body quenching of O₂(a ¹δ_g) by O(³ P) limits the singlet oxygen yield with increasing pressure. The fast removal of atomic oxygen both in discharge and in the earlier afterglow could provide DSOG scaling with pressure.     

Determination of the ππ scattering lengths from data on πN → ππN reactions by the method of Roy equations

Fitted phase-shift curves from the threshold to the dipion mass, which is equal to 1 GeV, are constructed on the basis of all available experimental values of the S-and P-wave phase shifts for five charged channels of pion-pion scattering. The resulting phase-shift curves are introduced in the Roy equations in order to obtain the subtraction constants λ _l ^I (s). By using these subtraction-constant values as functions of the dipion mass, the S ₀-and S ₂-wave pion-pion scattering lengths are found to be a ₀ ⁰ = (0.240 ± 0.023)m _π ^?1 and a ₀ ² = (?0.034 ± 0.013)m _π ^?1 . A strong correlation of the S-wave scattering lengths is demonstrated.     

Cover Picture: Contrib. Plasma Phys. 7/2013

A 250 µm thick high purity beryllium foil is symmetrically irradiated by a total of 20 laser beams at 351 nm wavelength. Each laser carries 480 J in a 1 ns long pulse, the pulses are staggered in time and focussed on a 800 µm diameter focal spot, yielding a flat top intensity profile of 2.4 × 10¹⁴ W/cm² for 3 ns on the target surface. The evolution of the mass density is modelled with the radiation‐hydrodynamics code HELIOS as function of the target depth. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparison of electron spin polarization of P 870 + Qa a − observed in Zn2+-containing and Fe2+-depleted bacterial reaction centers

Recently, a general model has been developed to explain electron spin polarized (ESP) electron paramagnetic resonance (EPR) signals found in systems where radical pairs are formed sequentially. The photosynthetic bacterial reaction center (RC) is such a system in which we can experimentally vary parameters (lifetime, structure, and magnetic interactions in the sequentially formed radical pairs) that affect ESP development in order to test this model. In Fe²⁺-depleted transfer step from intermediate radical pair, P ₈₇₀ ⁺ Q _a ^? which is produced in an electron transfer step from intermediate radical pair, P ₈₇₀ ⁺ I^?. (P ₈₇₀ ⁺ is the oxidized primary donor, a special pair of bacteriochlorophyll molecules, I^? is the reduced bacteriopheophytin acceptor, and Q _a ^? is the reduced primary quinone acceptor.) The lifetime of P ₈₇₀ ⁺ I^? can be shortened relative to the lifetime of P ₈₇₀ ⁺ I^? in Fe²⁺-depleted RCs by substitution of Zn²⁺. We report the first observation of X-band and Q-band ESP EPR signals due to P ₈₇₀ ⁺ Q^? from bacterial reaction centers that contain Zn²⁺. Comparison of these signals to those observed from Fe²⁺-depleted bacterial reaction centers shows intensity differences and g-factor shifts. The results are discussed in terms of the general sequential radical pair model.     

Theory of self-locking phenomena in the pressure broadened three-mode He-Ne laser

Taking account of pressure broadening the coefficients in Lamb's third-order amplitude and phase determining equations for three modes are evaluated in the Doppler limit, and comparison is made with other theories. After expanding the coefficients to first order in the detuning ε from the linecenter an expression is presented for the frequency range where mode locking will occur. Using experimental data of several authors for the 6328 Å Ne-transition numerical values are obtained for the pressure dependent decay rates Υ _a , Υ _b , of the upper and lower laser level and the linewidth Υ _ab ^′ , viz.:Υ _a =17.7+(12.6±0.6)P _He, Υ _b =8.3+(12.6±0.6)P _He, and Υ _ab ^′ =13.0+(91±6)P _He MHz, whereP _He is measured in torr.     

The 235 ns 9+ isomer in 63 148 Eu85

From (p, xn) in-beamγ-ray and electron measurements aT _1/2=235(14) ns isomer at 720 keV was identified in ₆₃ ¹⁴⁸ Eu₈₅ and the levels populated in its decay have been characterized. The results determineI ^π=9⁺ for the isomeric state, and we assign it as the (πh _11/2 j ₀ ^?2 ν f ₇ ^2/3 )9⁺ shell model state, analogous to the configuration of the 235 μs isomer in ₆₃ ¹⁴⁶ Eu₈₃.     

Bandbreite im Threshold-Bereich des 0.63 μ He/Ne-Lasers

A double laser device of high stability was used to determinate the threshold bandwidth of a He/Ne-laser amplifier and oscillator. I. Using one laser as a single-mode oscillator, the other as an amplifier, resonance curves of the amplifier with bandwidths between_IΔv=2.5 · 10³ and 1.7 · 10⁶ Hz were recorded. II. Operating the two lasers as single-mode oscillators, beat frequencies with a bandwidth_IIΔv?100 Hz were observed. Extrapolating these results to the threshold noise power the threshold-bandwidths_IΔv _R ^* =1.4 · 10³ Hz and_IIΔv _R ^* =2.0 · 10³ Hz, respectively, are obtained.     

Evidence for a newK * \bar K state at a mass of 1,530 MeV withIJ PC=01++ observed inK − p interactions at 4.2 GeV/c

Evidence is presented for a newK ^* \(\bar K\) +c.c. resonance with a mass of (1,526±6) MeV, a width of (107±15) MeV and quantum numbersIJ ^PC=01⁺⁺. We call itD′ meson. Initially it is observed as aK ^* \(\bar K\) +c.c. enhancement in the reactionsK ^? p→(K _s ⁰ K ^±π^?)Λ at 4.2 GeV/c. The isospin assignmentI=0 comes from its further observation in the reactionsK ^? p→(K _s ⁰ K ^±π^?)Σ ⁰ andK ^? p→(K _s ⁰ K ^±π^?)Σ(1,385)⁰ but not inK ^? p→(K ⁺ K ^?π^?)Σ⁺ orK ^? p→(K _s ⁰ K ^±π^?)Σ(1,385)⁺. A maximum likelihood analysis of the (K \(\bar K\) π) decay Dalitz plots in the reactionsK ^? p→(K _s ⁰ K ^±π^?) determines theJ ^PC of theD′ meson to be 1⁺⁺. A satisfactorySU(3) fit is obtained to a 1⁺⁺ nonet composed of theI-1A ₁, theI=1/2Q _A with theD(1,285) and theD′(1,526) as theI=0 members having a mixing angle close to the magic one.     

Up-conversion and population of excited erbium levels in LiY1−x ErxF4 (x=0.003–1) crystals under CW InGaAs laser-diode pumping

Formation of the inverse population of working levels of 3-μm laser transition in LiY_1−x Er_xF₄ (x=0.003–1) crystals under CW InGaAs laser-diode pumping (0.967–0.982 μm) was investigated. Dependences of population of the ⁴ I _11/2 and ⁴ I _13/2 levels on the dopant concentration and pump power were studied theoretically and experimentally. Relative changes in populations of the studied levels were experimentally monitored by measuring the steady-state spectra of IR crystal luminescence in the wavelength range corresponding to ⁴ I _11/2→⁴ I _13/2 (2.7–2.8 μm), ⁴ I _11/2→⁴ I _15/2 (0.96–1.04 μm), and ⁴ I _13/2→⁴ I _15/2 (1.45–1.65 μm) transitions. Theoretical and experimental estimates of the rates of intracenter and intercenter relaxation processes (migration, self-quenching, and up-conversion) with allowance for statistics of coupling of impurity centers in the system were used to determine the energy-transfer mechanisms, elucidate the predominant mechanisms, and obtain microparameters and concentration dependences of the energy-transfer rates and nonlinear coupling. Dependences of the steady-state population of the levels of laser transition ⁴ I _11/2→⁴ I _13/2 on the dopant concentration and pumping power density were calculated within the context of rate balance equations for the scheme with the five lowest excited states of erbium. Good agreement between theory and experiment was obtained. __________ Translated from Optika i Spektroskopiya, Vol. 92, No. 1, 2002, pp. 73–88. Original Russian Text Copyright ? 2002 by Tkachuk, Razumova, Mirzaeva, Malyshev, Gapontsev.     

Effects of sidelobes of focused flat-topped laser beams on vacuum electron acceleration

Using three-dimensional test particle simulations, we investigated electrons accelerated by a focused flat-top laser beam at different intensities and flatness levels of the beam profile before focusing in vacuum. The results show that the presence of sidelobes around the main focal spot of the focused flat-top laser beam influences the optimum (as far as electron acceleration is concerned) initial momentum (and incident angle) of electrons for acceleration. The difference of initial conditions between laser beams with and without sidelobes becomes evident when the laser field is strong enough (a₀>10, corresponding to intensities I>1×10²⁰ W/cm² for the laser wavelength λ=1 μm, where a₀ is a dimensionless parameter measuring laser intensity). The difference becomes more pronounced at increasing a₀. Because of the presence of sidelobes, there exist three typical CAS (capture and acceleration scenario) channels when a₀≥30 (corresponding to I>1×10²¹ W/cm² for λ=1 μm). The energy spread of the outgoing electrons is also discussed in detail. PACS 41.75.Jv; 42.60.Jf; 42.25.Fx     

On continuity of Bowen-Ruelle-Sinai measures in families of one dimensional maps

Let us consider a family of mapsQ _a (x)=ax(1?x) from the unit interval [0,1] to itself, wherea∈[0,4] is the parameter. We show that, for any β<2, there exists a subsetE?4 in [0,4] with the properties

1. Leb([4??,4]?E) < ?^β for sufficiently small ?>0,
2. Q _a admits an absolutely continuous BRS measure µ_a whena∈E, and
3. µ_a converges to the measure µ₄ asa tends to 4 on the setE. Also we give some generalization of this results.

     

K-capture probabilities in the electron capture decay of159Dy

TheK-electron capture probabilities (P _k) for the 58 keV state and the ground state of¹⁵⁹Tb in the decay of¹⁵⁹Dy have been determined. The measured values,P _k ⁵⁸ =0.81±0.05 andP _k ⁰ =0.79±0.06 are found to be in excellent agreement with theoretical results.     

A new molecular C60 complex with bis(methylenedithio)tetrathiafulvalene (BMDT-TTF): Synthesis, crystal structure, and properties

A new molecular C₆₀ complex of the composition (BMDT-TTF) · C₆₀ · 2CS₂ (I) with the bis(methylenedithio)tetrathiafulvalene (BMDT-TTF) organic donor is synthesized. The molecular and crystal structures of this complex are determined by x-ray diffraction. The (BMDT-TTF) · C₆₀ · 2CS₂ (I) compound crystallizes in a monoclinic crystal system. The main crystal data are as follows: a=13.550(5) Å, b=9.964(7) Å, c=17.125(8) Å, β=99.52(4)°, V=2280(2) ų, M=1229.45, and space group P2₁/m. Crystals of I have a layered structure: layers consisting of C₆₀ molecules alternate with layers composed of BMDT-TTF and CS₂ molecules. It is found that, in complex I, the donor and C₆₀ molecules are linked through the shortest contacts, which leads to a change in the molecular geometry of BMDT-TTF. The donor molecules in a crystal layer are characterized by the shortest S...S contacts. The IR data indicate the electroneutrality of the fullerene molecule. The electrical conductivity of (BMDT-TTF) · C₆₀ · 2CS₂ single crystals is measured using the four-point probe method at room temperature: σ_RT=2×10^?5 Ω^?1 cm^?1.     

A new many-body solution of the Friedel resonance problem

It is numerically shown that the groundstate of the Friedel problem (consisting of a conduction band and a dresonance), occupied with (n+ 1) electrons, can be written as Ψ = (A a ₀ ^* +Bd*) Π _v=1 ⁿ a _v ^* Φ₀, where a ₀ ^* represents a localized conduction electron state, d* is the Friedel resonance state and Π _v=1 ⁿ a _v ⁸ Φ₀ is a Slater determinant of n single electron states a _t ^* , (Φ₀ is the vacuum state). The a _i ^* together with a ₀ ^* are part of a full ortho-normalized basis of the conductions band.     

Nuclear spin relaxation of Xe in liquid Te

By the method of time differential perturbed angular distribution following a nuclear reaction, the relaxation rateT _r ^?1 of the 8 msI ^π=10⁺ isomer of¹³²Xe has been measured in liquid Te. Between 670 °K (supercooled liquid) and 1,000 °K the rate decreases from about 720/s by about a factor of two. From existing experimental material it is concluded thatT _r ^?1 is mainly due to quadrupolar interaction (T _r ^?1 ≈T _Q ^?1 ). Its magnitude is discussed considering the metallic and the noble gas limit as models for the Xe-Te-interactions. The temperature dependenceT _Q(T) apparently does not correlate with the diffusion constant of Te in contrast to a simplified theoretical treatment. — The nuclearg value of the isomer has been determined to be g=(?)0.195(5) thus confirming the configuration (vh_11/2)².     

Perturbed angular distribution of recoil implanted F19-nuclei in a nickel-environment

Magnetic hyperfine fields acting on F¹⁹ in a Nickel lattice have been investigated. Time-dependent spin rotation has been observed following the excitation and recoil implantation with a pulsed proton beam using the reaction F¹⁹(p,p′)F¹⁹?. Two hyperfine fields were detected at 290 °K:H _hf ⁽¹⁾ =+17.6 ± 0.5 kGH _hf ⁽²⁾ =+91 ± 3 kG. The variation of the effective fields with the external polarizing field was studied. The mean life of the 197 keV level has been remeasured as τ=128±2 nsec.     

Low energy π-π resonances in the Veneziano model

We attempt to impose elastic unitarity on the forward π-π scattering using the Veneziano Amplitude together with a crossing symmetric subtraction term as an input. TheN/D method is used and thep, ? mesons are interpreted as CDD poles. The self consistency requirement led to the evalutation of the low energy parameters and theS andP-wave phase shifts. The values of the scattering lengths obtained area ₀ ⁰ =0.084m _π ^?1 ,a ₂ ⁰ =?0.024m _π ^?1 ,a ₁ ¹ =0.047m _π ^?3 .     

Parametrization of two-body perturbation on atomic fine and hyperfine structure. The configuration (6p)3 in the bismuth atom

A method of simultaneous parametrization of one- and two-body interactions on atomic hyperfine structure of configurationl ^N is proposed and applied for the analysis of the configuration (6p)³ in the bismuth atom. For this purpose, the hyperfine structure splittings of the levels²D ₃ ^2/0 ,²D ₅ ^2/0 and²P ₁ ^2/0 were measured. The finally obtained values of HFS parameters are: for one-body parameters (in MHz):a _p ⁰¹ =2,537(9),a _p ¹² =5,182 (12),a′¹⁰=?2,019(10),b _p ⁰² =?3,198(53),b _p ¹¹ =2,816(54); for two-body parameters (in MHz):x _pp ^′/01 ,₂=284(3),x _pp ^′/12 ,₂=581(5),x _pf ^′/12 ,₂=170(70),x _pp ^′/02 ,₂=?359(36),x _pf ^′/02 ,₂=?33(100). The value of the quadrupole moment of the nucleus ₈₃ ²⁰⁹ Bi is also discussed.     

Optical determination of the nuclear moments of137La

Using the reactor-produced lanthanum isotope ₅₇ ¹³⁷ La, the hyperfine structure (hfs) of the transition La I, 5d ² 6p z ⁴ G ₁₁ ^2/0 ?5d ² 6s a ⁴ F _9/2, λ=6250 Å and La I, 5d ² 6p z ² H ₁₁ ^2/0 ? 5d ² 6s a ²G_9/2, λ=6266 Å were measured by means of a Fabry-Pérot interferometer. The nuclear spin I (¹³⁷La)=7/2, already theoretically estimated by earlier authors, was confirmed. The nuclear magnetic dipole moment μ_I(¹³⁷La)=+ 2.690 (6) n.m. and the electric quadrupole momentQ(¹³⁷La)=+ 0.26 (8) · 10^?24 cm² were determined from the ratios of the hfs interaction constantsA andB of¹³⁷La and the natural¹³⁹La.