Hyperfine structure and nuclear moments of99Ru and101Ru

The atomic-beam magnetic-resonance method in combination with the triple resonance technique has been used to determine the nuclear magnetic dipole moments of⁹⁹Ru and¹⁰¹Ru. The moments are deduced fromrf transition measurements in the⁵F₅ and⁵F₄ states at magnetic fields between 770 and 2400 Oe. In order to reduce the part of the uncertainty of the moments which arises from the uncertainty of the hyperfine structure constants more precise values of the constants than those available up to now were determined from low field measurements. After making corrections for hyperfine and Zeeman interactions with neighbouring atomic states we obtain the following values for the magnetic dipole moments:μ ₉₉=?0.6381 (51)μ _N andμ ₁₀₁=?0.7152 (60)μ _N (uncorrected for diamagnetic shielding). The results of the present work combined with the results of an earlier hyperfine structure investigation in the⁵F multiplet are analysed with respect to the effective-operator formalism. From this analysis we obtain the following values for the electric quadrupole moments:Q ₉₉=0.076 (7) b andQ ₁₀₁=0.44 (4) b (uncorrected for Sternheimer shielding or antishielding).     

99Ru,61Ni,57Fe,and119Sn Mössbauer studies of Heusler alloys containing ruthenium

⁹⁹Ru,⁶¹Ni,⁵⁷Fe and¹¹⁹Sn Mössbauer spectroscopic studies were made on ternary intermetallic compounds containing ruthenium, Ru_xY_3?xZ (Y=Fe, Ni; Z=Si, Sn). In the system of Ru_xFe_3?xSi, two different hyperfine magnetic fields were observed at the⁹⁹Ru nuclei (H _hf[Ru]) in the range ofx≤1.0 and the magnitude of eachH _hf[Ru] was found to decrease with an increase in the ruthenium concentrationx. Both the⁹⁹Ru and¹¹⁹Sn Mössbauer spectra of Ru₂FeSn could be analyzed with two sets of magnetically split lines. The⁶¹Ni Mössbauer spectra of Ru₂NiSn were obtained at 5 and 77 K.     

Nuclear orientation study of97, 103, 105Ru in Fe

Angular distributions have been measured forγ-rays emitted following the decays of^{97, 103, 105}Ru oriented in an iron matrix at temperatures down to 2.8mK. From the temperature dependence of theγ-anisotropies the magnetic hyperfine splitting frequenciesν _M =|gμ _N B _HF/h| of^{97, 103, 105}RuFe were found to be 110(7), 57(15) and 80 _?50 ⁺¹⁷ MHz, respectively. With the known hyperfine fieldB _HF=?489.6(4.0) kG the nuclearg-factors are derived as ∣g(⁹⁷Ru;j ^π=5/2⁺)∣=0.29(2), ∣g(¹⁰³Ru;j ^π=3/2⁺)∣=0.15(4) and ∣g(¹⁰⁵Ru;j ^π=3/2⁺)∣=0.21 _-0.13 ^+0.05 . The analysis for¹⁰³RuFe has been performed with the assumption ofj ^π=3/2⁺ and 5/2⁺ for the ground state of¹⁰³Ru. Taking into account experimentally knowng-factors of 3/2⁺ and 5/2⁺ states in this mass region, our data strongly favour the assignmentj ^π=3/2⁺ for the¹⁰³Ru ground state.     

Hyperfine structure measurements in the ground states5 F 5,5 F 4,5 F 3 and5F2 of99Ru and101Ru with the atomic beam magnetic resonance method

The hyperfine structure of the four lowest levels⁵ F _{5, 4, 3, 2} of the⁵ F ground state multiplet arising from the configuration 4d ⁷ 5s in⁹⁹Ru and¹⁰¹Ru has been studied by the atomic — beam magnetic — resonance technique. After applying corrections due to the effects of off-diagonal hyperfine mixing we obtain the following multipole interaction constants:⁹⁹Ru:A(⁵ F ₅)=?204.5514(33) MHzB(⁵ F ₅)=27.281 (62) MHzA ⁵ F ₄=?163.6845(36) MHzB(⁵ F ₄)=17.455(52) MHzA ⁵ F ₃=?135.0294(37) MHzB(⁵ F ₃)=10.164(50) MHzA(⁵ F ₂)=? 82.5325(27) MHzB(⁵ F ₂)=5.457(22) MHz¹⁰¹Ru:A(⁵ F ₅)=?229.2881(33) MHzB(⁵ F ₅)=158.934(62) MHzA(⁵ F ₄)=?183.4744(36) MHzB(⁵ F ₄)=101.799(52) MHzA(⁵ F ₃)=?151.3502(38) MHzB(⁵ F ₃)=59.323(50) MHzA(⁵ F ₂)=?92.4974(27) MHzB(⁵ F ₂)=31.869(23) MHz. The magnetic dipole and the electric quadrupole moments of the⁹⁹Ru and¹⁰¹Ru nuclear ground states as calculated from these constants are the following:μ _I (⁹⁹Ru)=?0.594(119) nmQ(⁹⁹Ru)=0.077 (15) barnsμ _I (¹⁰¹Ru)=?0.666(133)nmQ(¹⁰¹Ru)=0.45 (9) barns. From measurements of the Zeeman effect in the even isotope¹⁰²Ru we find the followingg _J -factors for the⁵ F ground multiplet:g _J (⁵ F ₅)=1.397741(20)g _J (⁵ F ₄)=1.347604(20)g _J (⁵ F ₃)=1.248988(20)g _J (⁵ F ₂)=1.001120(3).     

Isomer shifts and changes of the nuclear charge radii in99Ru and101Ru

The recoilless nuclear gamma resonance of the 127 keV γ-rays of¹⁰¹Ru was observed in ruthenium metal, RuO₂ and [Ru(NH₃)₄(HSO₃)₂]. By comparison of the isomer shifts observed in these materials for the 127 keV absorption line with the corresponding shifts of the 90keV γ-rays of⁹⁹Ru one obtains δ〈r ²〉 [127 keV]/ δ〈r ²〉 [90 keV]=1.78±0.26 for the ratio of the changes of the mean square nuclear charge radii between the first excited and the ground states in these nuclei. An estimate of electron density differences based on free-ion relativistic self-consistent field calculations yields δ〈r ²〉[90keV]≈+1.4·10^?3 for⁹⁹Ru and δ〈r ²〉/〈r ²〉 [127 keV]≈+2.4·10^?3 for the¹⁰¹Ru case. These results are discussed in terms of the core excitation model.     

TDPAC andemission Mössbauer studies of Fe3O4(99Ru)

Hyperfine interactions of⁹⁹Ru(»⁹⁹Rh) nuclei in Fe₃O₄ were studied by means of TDPAC andemission Mössbauer spectroscopy. The isomer shift obtained from an emission Mössbauer spectrum andthe temperature dependence of the hyperfine magnetic field obtained from TDPAC measurements indicate that⁹⁹Ru ions arising from⁹⁹Rh nuclei dilutely doped in Fe₃O₄ exist as a mixed state of Ru²⁺ andRu³⁺, which is not common in ruthenium oxides. Fe₃O₄(⁹⁹Ru) is the first example where a Ru ion in a low valence state exhibits its own magnetization in oxides.     

Anomalous temperature dependence of the magnetic hyperfine field of99Ru in gadolinium

The magnetic hyperfine field at dilute⁹⁹Ru impurities in ferromagnetic Gd has been investigated as a function of temperature by time differential perturbed angular correlation (TDPAC) measurements. The saturation field at 11 K is H_hf(Ru Gd)=51(2) KOe. This value fits well into the systematics of 4d impurity hyperfine fields in Gd. The magnetic hyperfine field of RuGd does not follow the magnetization of the host (T_c=290 K) but vanishes abruptly at about 70 K. A similar behaviour has previously been observed for the 5d impurity Os in Gd. From first TDPAC measurements of the hyperfine interactions in the intermetallic phases of the Ru-Sc system it can not be completely ruled out that the observed collapse of the hyperfine field at 70 K is due to the formation of the intermetallic compound RuGd₃.This work has been supported by the Minister für Wissenschaft und Forschung des Landes Nordrhein-Westfalen     

Spin-flipβ − decay of even-even deformed nuclei110Ru and112Ru

Neutron-rich nuclides¹¹⁰Ru and¹¹²Ru produced in symmetric fission of²³⁸U by 20 MeV protons have been studied at the IGISOL facility by means ofβ-ray,γ-ray and conversion electron spectroscopy. A total of 12 and 6γ-transitions were observed in the decays of¹¹⁰Ru and¹¹²Ru, respectively. Multipolarities were determined for a few transitions. The beta decay half-life was determined to be 11.6±0.6 s for¹¹⁰Ru and 1.75±0.07 s for¹¹²Ru. As a side product, a new value of 2.1±0.3 s for theβ half-life of the¹¹²Rh 1⁺ state was obtained. The decay energy measured with the plastic scintillator was 2.81 ±0.05 MeV for¹¹⁰Ru and 4.52 ±0.08 MeV for¹¹²Ru. The beta decay schemes of¹¹⁰Ru and¹¹²Ru isotopes indicate that the main fraction of their beta strength resides in two 0⁺→1⁺ spin-flip transitions with their logf t values between 4.4 and 4.7. The decay energies and the energies of the 1⁺ GT states are compared with the macroscopic-microscopic model calculations. The observed GT-strengths are discussed in the framework of the deformed single-particle model.     

Search for double- \beta decays of 96Ru and 104Ru by ultra-low background HPGe \gamma spectrometry

A search for double- $ \beta$ processes in ⁹⁶Ru and ¹⁰⁴Ru was realized in the underground Gran Sasso National Laboratories of the INFN (Italy) with the help of ultra-low background HPGe $ \gamma$ spectrometry. After 158h of data taking with 473g ruthenium sample, new improved limits on double-beta processes in ⁹⁶Ru have been established on the level of 10¹⁸-10¹⁹yr. For the first time the double-beta decay of ¹⁰⁴Ru to the 2⁺ ₁ excited level of ¹⁰⁴Pd has been restricted as T _1/2 > 3.5×10¹⁹ yr.     

The decay of105Tc to levels in105Ru

Theβ ^?-decay of 7.6-min¹⁰⁵Tc has been investigated byβ- andγ-ray singles and coincidence measurements. The activities have been produced by thermal-neutron-induced fission of²³⁵U or²³⁹Pu and subsequent chemical separation of the technetium fraction from the fission product mixture. AQ _β-value of 3.2±0.2 MeV has been determined. In a delayed coincidence experiment the lifetime of the first excited state in¹⁰⁵Ru at 20.55 keV has been measured to be 340±15 nsec. A level scheme of¹⁰⁵Ru is proposed and compared with the results of recent nuclear reaction studies like¹⁰⁴Ru(d, p) and¹⁰⁴Ru(n, γ). From beta branching ratios to levels in¹⁰⁵Ru, ground state spin and parity of 5/2⁺ can be suggested for¹⁰⁵Tc in accordance with the trend observed in neutron rich technetium isotopes.     

Ru L2,3 XANES theoretical simulation with DFT: A test of the core-hole treatment

Density functional theory (DFT)-based relativistic calculations were performed to model the Ru L-edge X-ray absorption near edge structure (XANES) spectra of the hexaammineruthenium complex [Ru(NH₃)₆]³⁺ and “blue dimer” water oxidation catalyst, cis,cis- [(bpy)₂(H₂O)Ru^IIIORu^III(OH₂)(bpy)₂]⁴⁺ (bpy is 2,2-bipyridine). Two computational approaches were compared: simulations without the core-hole and by modeling of the core-hole within the Z+1 approximation. Good agreement between calculated and experimental XANES spectra is achieved without including the core-hole. Simulations with algorithms beyond the Z+1 approximation were only possible in a framework of the scalar relativistic treatment. Time-dependent DFT (TD-DFT) was used to compute the Ru L-edge spectrum for [Ru(NH₃)₆]³⁺ model compound. Three different core-hole treatments were compared in a real-space full multiple scattering XANES modeling within the Green function formalism (implemented in the FEFF9.5 package) for the [Ru(Mebimpy)(bpm)(H₂O)]²⁺ complex. The latter approaches worked well in cases where spin–orbit treatment of relativistic effects is not required.     

The collective structure of106,108Ru

Levels in^106,108Ru have been studied by measuringγγ coincidences andγγ directional correlations of theγ-rays following theβ ^?-decay of 36 s¹⁰⁶Tc and 5 s¹⁰⁸Tc. Tc activities were separated chemically from the fission products of thermal neutron induced fission of²³⁹Pu by the continuously running system “SISAK 2” and theγ-radiation was measured on-line. An extended level scheme for¹⁰⁸Ru, spin assignments,E2/M1 multipole mixing ratios andB(E2) ratios for¹⁰⁶Ru and¹⁰⁸Ru have been obtained. The collective structure of the two nuclei is discussed in the framework of different nuclear models.     

Magnetic properties and Eu hyperfine interactions in EuSr2Ru1−xO6 (x=0 and 0.2)

Magnetization studies show that nonsuperconducting RSr₂Ru_1−xCu_xO₆ (R=Eu and Gd) compounds are magnetically ordered below T_N=31 K regardless of R and Cu concentration. The magnetic ordering is due to the Ru sublattice. Mössbauer effect studies reveal that the Ru magnetism induces a magnetic moment (0.35 μ_B) and a magnetic hyperfine field (270 kOe) in the otherwise nonmagnetic Eu³⁺ ions, and that the Ru magnetization lies in the basal plane.     

The level structure of92Ru up to high spin values

The level structure of⁹²Ru has been studied by means of γ-ray spectroscopy. The nucleus was produced by the⁵⁸Ni(⁴⁰Ca, α2p)⁹²Ru reaction at beam energies of 147 and 187 MeV. The NORDBALL detector system including particle selection was used. A large number of new levels with excitation energies up to 11.3 MeV and spin values up to 22 or 23 units of angular momentum have been established. The level scheme is compared with recent shell model calculations using¹⁰⁰Sn as a core. Some systematics of the g ₉ ^2/?2 configuration is discussed and a strong correlation between the levels in⁹⁰Mo and⁹²Ru is found.     

Alignments and band termination in99,100Ru

h11/2 neutron and g9/2 proton alignments in ^99,100Ru deduced from comparisons of experimental Routhians and aligned angular momenta to cranking model calculations. There is indication of band termination in¹⁰⁰Ru.     

Gamma spectroscopic study of105Ru

Theγ radiation following thermal neutron capture in¹⁰⁴Ru has been investigated through singles, coincidence, and angular correlation measurements in order to solve existing discrepancies and to complete the knowledge about the transitional odd-N nucleus ₄₄ ¹⁰⁵ Ru₆₁. The resulting level andγ-decay scheme is found to be very similar to that of the odd-Z transitional nucleus ₆₁ ¹⁴⁹ Pm₈₈. Between the 11/2^?, 15/2^?, and 19/2^? states which are interpreted as members of the decoupled band, built on the unique parity 11/2^? single particle state, low spin states of negative parity are found at surprisingly low excitation energies above the 11/2^? state. In the frame of the particleplus-rotor model their positions would require a sharp decrease of the rotational parameter with increasing collective angular momentum of the soft core.     

Coadsorption of oxygen and sodium on Ru(001)

The interaction of oxygen with sodium predosed Ru(001) is studied by means of thermal desorption, Auger and electron loss spectroscopy and work function measurements. The initial sticking coefficient of oxygen is found to increase from 0.45 for bare Ru(001) to 1 for Ru(001) with a 0.35 monolayer sodium coverage. The adsorption capacity of the sodium predosed Ru(001) surface towards oxygen is enhanced from θ_O = 0.5 for clean Ru(001) to θ_O = 1.4 for Ru(001) with a 0.7 monolayer sodium coverage. The work function, electron loss changes and thermal desorption data give evidence that as long as θ_Na is less than 0.25, the oxygen chemisorption phase is characterized mainly by oxygen-Ru bonds and by the absence of strong sodium-oxygen interactions. At high sodium coverages (θ_Na > 0.35), the experimental data indicate the formation of a Na-O compound in the second adsorption layer at high oxygen exposures. When Ru(100) is predosed with sodium (θ_Na ? 0.25), this leads to complete suppression of oxygen penetration into the bulk during heating, the latter process being observed for the oxygen-Ru(001) system.     

Levels in 106Ru and 108Ru

The decay schemes of 36 s ¹⁰⁶Tc and 5 s ¹⁰⁸Tc have been studied with γ-ray singles and γ-γ coincidence measurements. To separate the technetium nuclides from the fission products of ²³⁹Pu, an on-line chemical separation procedure has been developed which is based on multistep chemical separations of liquid phases by fast-rotating centrifuges (“SISAK”). The resulting level schemes of ¹⁰⁶Ru and ¹⁰⁸Ru, together with those of ¹⁰²Ru and ¹⁰⁴Ru, are interpreted in terms of the generalized collective model of Gneuss and Greiner. The potential-energy surfaces calculated from the spectroscopic data show a trend towards triaxial shapes for the very neutron-rich Ru nuclei.     

Description of mixed symmetry states in <Superscript>96</Superscript>Ru using IBM-2

We have investigated the properties of low-lying states in ⁹⁶Ru within the framework of the neutron-proton interacting boson model (IBM-2), with special attention paid to the characteristics of the mixed symmetry states. By considering the relative energy of d proton boson to be different from that of neutron boson, the level energies and M1, E2 transition strengths have been calculated. The IBM-2 calculation is consistent with the experimental data of ⁹⁶Ru both quantitatively and qualitatively. Particularly, the strong M1 transition between the 4₂ ⁺ and 4₁ ⁺ states has been reproduced nicely. The calculated results show that the M1 transition strength of B(M1; 4₂ ⁺ → 4₁ ⁺) in ⁹⁶Ru can be described successfully by the IBM-2.     

Low-spin structure of 113Ru and 113Rh

The ¹¹³Ru and ¹¹³Rh nuclei, produced in the spontaneous fission of ²⁴⁸Cm and in proton-induced fission of ²³⁸U , were studied by means of prompt gamma spectroscopy using the EUROGAM 2 array of Anti-Compton spectrometers and the IGISOL mass separator, respectively. For the 0.5s isomer, found in ¹¹³Ru in our recent study we propose the 7/2^-[523] configuration. The present data indicate spin and parity 1/2⁺ for the ground state in ¹¹³Ru . This and some new data on the excited levels in ¹¹³Rh allows reinterpretation and a better understanding of the β^- _{} decay scheme of ¹¹³Ru . The properties of ¹¹³Ru were studied in the frame of the Core-Quasiparticle Coupling model, which has well reproduced the experimental data.