Hyperfine magnetic anomaly in isotopic pairs <Superscript>151, 152</Superscript>Eu and <Superscript>152, 153</Superscript>Eu

High-resolution laser spectroscopy measurements of optical hyperfine splitting on the ^{151, 152, 153}Eu isotopes were performed on the atomic transition 4f ⁷6s ^{2 8} S _7/2 → 4f ⁷6s6p ⁶ P _5/2 at λ ≈ 564.58 nm. Values of the nuclear magnetic dipole and electric quadrupole moments are obtained from the measured hyperfine splitting and the magnetic hyperfine anomalies in the isotope pairs ^{151, 152}Eu and ^{152, 153}Eu are deduced. The absolute values of the hyperfine anomaly in both cases are unusually large: 5 (1)%. The possible sources causing these anomalies are discussed.     

A high resolution study of the transitions 4f 76s 2→4f 76s6p in the Eu I-spectrum

Eight transitions in the Eu I-spectrum connecting the ground state with configuration 4f ⁷ 6s ² with states of the configuration 4f ⁷ 6s6p were studied with high resolution laseratomic-beam spectroscopy. CW dye lasers operating in the wavelength regions 435–470 nm and 560–630 nm were used for this study. New data for the hyperfine structure in¹⁵³Eu were obtained as well as new and more accurate values for the isotope shifts between¹⁵¹Eu and¹⁵³Eu. The existing data for the hyperfine structure in¹⁵¹Eu were reproduced with an exception for the levelz ⁶ P _7/2.     

Hyperfeinanomalie im151Eu und153Eu

Using the Mössbauer effect, the ratios of theg factors and the hyperfine splitting constants for the 21.6 keV state and the ground state in¹⁵¹Eu and of the 103 keV state and the ground state in¹⁵³Eu have been measured. From these results values for the hyperfine anomaly of⁰Δ ₁₅₁ ²² =?0.81(8)% and⁰Δ ₁₅₃ ¹⁰³ =+ 1.8(8)% have been derived for¹⁵¹Eu and¹⁵³Eu, respectively.     

Laser-atomic-beam spectroscopy of 4f 75d6s−4f 75d6p transitions in Eu I

The hyperfine structure and the isotope shift of transitions between metastable levels of the configuration 4f ⁷5d6s and levels of the configuration 4f ⁷5d6p of¹⁵¹Eu and¹⁵³Eu were studied by means of the high resolution laser-atomic-beam technique. The metastable states were populated by an arc discharge burning in the atomic beam. The measured hyperfine constantsA andB of the 4f ⁷5d6s configuration allow to perform a parametric analysis using the effective tensor operator formalism. For the first time the nuclear quadrupole moments are deduced from the quadrupole interaction parameters of the 5d electron in Eu I. The values uncorrected for the Sternheimer effect are¹⁵¹ Q(5d)=1.53(5)b and¹⁵³ Q(5d)=3.92(12)b. A comparison with the quadrupole moments derived from the 6p electron and the intrinsic quadrupole moment of¹⁵³Eu gives information about Sternheimer's correction factors. The value found for the hyperfine anomaly due tos electrons in the 4f ⁷5d6s configuration agrees very well with previous results in other Eu configurations. The change in the mean-square nuclear charge radius is derived from the isotope shift measurements and compared with the results obtained from other optical transitions in Eu. The mean value isgd〈r ²〉^{151, 153} =0.577(25) fm².     

Nuclear moments and isotope shifts of europium isotopes by hyperfine structure investigations with collinear laser — Ion beam spectroscopy

Hyperfine structures and isotope shifts of the transition 4f⁷(⁸S ₇ ^2/0 )6p_3/2 (7/2,3/2)₄?4f⁷(⁸S ₇ ^2/0 ) 5d⁹D ₄ ⁰ ,λ=604.95 nm, of stable¹⁵¹Eu and¹⁵³Eu and radioactive¹⁵²Eu and¹⁵⁴Eu have been investigated by collinear laser — ion beam Spectroscopy. Nuclear quadrupole moments have been derived.     

Bestimmung der Kernquadrupolmomente der beiden stabilen Europiumisotope aus dem Eu II-Spektrum

The hyperfine structure of the transitions 4f ⁷ 6p ⁹ P _3,4,5?4f ⁷ 6s ⁹ S ₄,⁷ S ₃ in the spark spectrum of europium was investigated by a digital recording double-Fabry-Perot-spectrometer. Enriched samples of¹⁵¹Eu and¹⁵³Eu were used in hollow cathode light sources cooled in liquid air. As the hyperfine splitting of the⁹ P levels was not completely resolved the patterns were analysed by a computer. TheA- andB-values of the⁹ P levels were determined for both isotopes. Together with the experimentalA-values of the⁷ P levels theseA-values were used to check the eigenfunctions ofBordarier, Judd, andKlapisch, which have been calculated for intermediate coupling. Good agreement between observed and calculatedA-values was reached only if the spherical-symmetric part of the magnetic hyperfine interaction operator of the 6p-electron was used as a free parameter. In this way the configuration interaction between 4f ⁷ 6p and 4f ⁶ 6s 6d can be taken into account. Fortunately this mixing does not affect the quadrupole interaction. Therefore the quadrupole moments were derived from the measuredB-values using the unperturbed eigenfunctions. The resultsQ(¹⁵¹Eu)=(1.12 ±0.07) · 10^?24 cm² andQ(¹⁵³Eu)=(2.85 ± 0.18) · 10^?24cm² are in complete agreement with the values obtained byMüller, Steudel, andWalther in the 4f⁷ 6s 6p levels of the arc spectrum of europium. The values found for the hyperfine anomaly agree very well with the values derived from levels in Eu I and Eu III.     

Cross sections and γ-rays from multiple neutron capture in151Eu

Primary capture gamma rays following multiple neutron capture in¹⁵¹Eu have been measured as a function of the irradiation time. Neutron capture cross sections of the¹⁵²Eu 3^? groundstate and of the¹⁵²Eu 0^? isomer (T _1/2=9.3h) were determined. These cross sections are relevant for the interpretation of inelastic scattering of neutrons at isomeric states with energy gain (neutron acceleration). The level scheme of¹⁵³Eu has been extended. Neutron binding energies of¹⁵²Eu,¹⁵³Eu,¹⁵³Gd and¹⁵⁴Gd are given.     

Half-life of the 89.83 keV level in152Eu

The half-life of the 89.83 keV level in¹⁵²Eu was measured in the¹⁵¹Eu(n, γ)¹⁵²Eu reaction to be 381±19 nsec. This results in the determination of the absolute transition probabilities of the 89.83 keVE1+M2 transition to the ground state, yielding hindrance factors relative to the Weisskopf estimateF _W(E1)=(2.3 ± 0.4) × 10⁶ andF _W=0.20±0.08.     

A muonic X-ray study of the charge distribution of 144, 148, 150, 152, 154Sm

We report the measurement of the energies of the 4f → 3d, 3d → 2p and 2p → Is muonic atomic transitions in separated isotopes of ^{144, 148, 150, 152, 154}Sm, and that of the 2s → 2p transitions of ¹⁵²Sm as well. Using these transition energies as well as the hyperfine splittings of the 2p levels, we have interpreted our data in terms of a deformed Fermi distribution for the charge density and obtained good fits. A model independent analysis of the isotope shifts in terms of generalized R_h moments has been made and is in good agreement with electronic X-ray and optical isotope shifts. The static quadrupole moments and the isomer shifts of the first excited state of ^{152, 154}Sm have been determined from the 2p hyperfine structure.     

Level crossing investigation of the hyperfine splitting in thez 6 P 7/2-level of EuI

By means of a level crossing experiment the hyperfine structure constants of thez ⁶ P _7/2-level of Eu have been determined. The results areA=-6.51(6) MHz andB= 131.2(1.0) MHz in the isotope¹⁵¹Eu andA=-2.84(3) MHz andB=327.5(1.5) MHz in the isotope¹⁵³Eu. Experimental data on the hyperfine splitting are available now for 11 of the 12 levels of the configuration 4f ⁷ (⁸S)6s 6p of EuI. These data are compared with the theoretical interpretation given by Bordarieret al. [1] which was based on only 7A-factors andB-factors. It is shown that the agreement between theory and experiment can be improved by taking into account configuration interactions.     

Nuclear levels in152Eu

The transitional nucleus¹⁵²Eu has been studied using the (n, e), (n, γ), (n _res,γ), (n, γγ), (d, p), (d, t) and (p, d) reactions. The experiments have been performed at nine different laboratories. A model independent level scheme was established including 95 levels below 510 keV and nearly 900 transitions by combination of low energy transitions and reaction data. More than 20 additional levels result from gamma rays and/or charged particle reactions. The level scheme is interpreted in terms of the Nilsson model indicating that¹⁵²Eu is a deformed nucleus. Seven rotational bands and Nilsson configurations are established. An additional 27 rotational bands are tentatively or speculatively assugned. Gallagher-Moszkowski splittings are discussed. The neutron binding energy was determined as 6305.2±0.5 keV. The energy of the 9.3 h 0^? isomer is 45.599 keV. The lifetimes of four levels were measured. Nuclear Reactions¹⁵¹Eu(n,γ),E _n =thermal and resonance; measuredE _γ ,I _γ ,E _c.e.,I _c.e.,γγ Coinc.,γγΔt coinc.;¹⁵¹Eu(d, p),E=12MeV and 14MeV;¹⁵³Eu(d, t),E=12MeV;¹⁵³Eu(p, d),E =18MeV; deduced level scheme of¹⁵²Eu,J, π, T _1/2,cc, Nilsson configurations. Magnetic electron spectrometer, curved crystal spectrometer, Ge(Li) and Si(Li) detectors, magnetic spectrographs. Enriched targets.     

Excited states in124Xe

The isomer shift in the optical transition Eu II 4f⁷(⁸S ₇ ^2/o )⁶p_3/2 ^(7/2,3/2)4?4f⁷ (⁸S ₇ ^2/o )5d⁹D ₄ ^o , λ=6O4.95 nm, has been measured between the isotope^152gEu(3^?) and its isomer^152mEu(0^?). From the valuev(^152gEu)–v(^152mEu)=736(10) MHz the deformation parameter of^152mEu has been estimated to be^152mβ?+0.25. This value is smaller than^152gβ as obtained from isotope shift measurements and the spectroscopic quadrupole moment. The influence of the shape difference on the decay of^152mEu is discussed.     

Hyperfeinstrukturuntersuchungen mit einem sphärischen Fabry-Perot-Interferometer mit internem Absorptionsatomstrahl im Tm I- und Eu I-Spektrum

A spherical Fabry-Perot spectrometer with an absorbing atomic beam passing the interior of the interferometer is described. By use of the internal beam it is possible to reduce the amount of material needed for the atomic beam source to a few milligrams per hour. The set-up is especially suitable for hyperfine structure and isotope shift investigations. For the photoelectric recording of the signal the geometrical distance between the spherical mirrors was changed using the piezoelectric effect. In order to reduce the influence of the intensity distribution of the light sourceI ₀(λ) the ratio [I ₀(λ)-I(λ)]/I ₀(λ) was measured, whereI ₀(λ)=I ₀(λ) exp (—V·k(λ)·d) is the observed intensity with absorbing atoms between the mirrors, andV the increase of the absorption signal due to the multiple reflections of the light through the atomic beam (V≈75). For an accurate and easy evaluation of the data this ratio was measured by a digital voltmeter and punched into paper tape. The small line width of the absorption profile obtained in the experiments with Tm and Eu enabled us to measure hyperfine distances of the order of 5 · 10^?3 cm^?1 to 20 · 10^?3 cm^?1 with an error not exceeding 0.1 · 10^?3 cm^?1 in some cases. From the measurements theA-factors for five levels of the configurations 4f ¹³6s 6p and 4f ¹²5d 6s ² in Tm I and theA- andB-factors of the stable Eu isotopes of the 4f ⁷ 6s 6p y ⁸ P _5/2level in Eu I were determined.     

Levels in154Eu populated by thermal neutron capture

The level scheme of¹⁵⁴Eu has been investigated by means of thermal neutron captureγ-rays and conversion electrons. The high energyγ-ray spectrum from thermal neutron capture in enriched¹⁵³Eu has been studied in the energy range of 5700 to 6500 keV. Low energyγ radiation has been observed with Ge(Li) and Si(Li) detectors from 5 to 300 keV and conversion electrons have been measured from 15 to 300 keV. Low energy (n, γγ) coincidences and half lives of transitions have been measured. The data, combined with three very recent studies of the 8^? isomer decay in¹⁵⁴Eu has led to the construction of a level scheme with 12 excited levels. Nuclear Reaction¹⁵³Eu(n, γ),E _n =thermal, measuredE _γ ,I _γ ,E _ce ,I _ce ,γγ-coincidence, halflives,¹⁵⁴Eu deduced levels.     

Determination of isotope shift crossed-second-order-effects and hyperfine-structure parameters in the Eu I configuration 4f 7 6s7s

In the Eu I configuration 4f ⁷(⁸ S)6s7s the isotope shift (IS) and hyperfine-structure (hfs) of the levelse ⁸ S _7/2 andf ⁸ S _7/2 were determined from the transitions 684.5 nm, 733.7 nm and 821.0 nm to 4f ⁷6s6p. Together with experimental results of our previous measurements a theoretical analysis of the IS and hfs for the complete configuration 4f ⁷ 6s7s can now be carried out. From the IS of the four 6s7s-levels we evaluated the two crossed-second-order-parametersg ₃(4f,6s)= ?l.l(l)mK andg ₃(4f, 7s)= ?0.1(l)mK. The ratiog ₃/G ₃ is determined for various Eu configurations and found to be equal to 5.6(3)·10^?6 in complete agreement with a theoretical value following from Hartree-Fock calculations. The single electron hfs splitting constantsa ¹⁰(4f)= ?1.9 (3) mK,a ¹⁰(6s)=396(3)mK, anda ¹⁰(7s)=65(3)mK are also determined and compared with those of other Eu configurations.     

Nuclear structure and the hyperfine interaction of oriented152Eu,155Eu,and153Gd in gold

Nuclear orientation of^152,155Eu and¹⁵³Gd in Gold has been used to determine the nuclear magnetic moment of¹⁵⁵Eu, (μ¹⁵⁵Eu)=1.93±0.26 n.m., and several mixing ratios of γ and β^? transitions in the decays. The hyperfine field of dilute EuAu alloys was found to beH _hf=134±10 kOe and for GdAu, |μH| was found to be in the range 0 to 1.0×10⁵ Oe·n.m.     

Spins,moments and charge radii in the isotopic series181Hg-191Hg

The hyperfine structure splitting and the isotope shift in the (6 s^{2 1}S₀ - 6s 6p³P₁,λ=2,537 Å) line of very neutron deficient Hg isotopes were determined by the β radiation detected optical pumping method (β-RADOP). In addition, nuclear magnetic resonance was observed in the atomic ground state. The results are Mean-square nuclear charge radii are calculated. Interpreting the sudden change of nuclear radius between¹⁸⁷Hg and¹⁸⁵Hg δ〈r²〉^187,185=0.42(5)fm² as oblate-prolate shape transition, one obtains δ〈β²〉 =0.054(5).     

Die Hyperfeinstruktur in den 4f7 6s 6p-Termen des Eu I und die elektrischen Kernquadrupolmomente von Eu151 und Eu153

The hyperfine structure of the statesz ¹⁰ P _11/2,z ¹⁰ P _9/2,z ¹⁰ P _7/2,z ⁸ P _9/2,y ⁸ P _9/2,y ⁸ P _7/2,y ⁸ P _5/2,z ⁶ P _7/2,z ⁶ 6s P _5/2 of the 4f ⁷ 6p configuration of EuI was investigated with a photoelectric recording Fabry Perot spectrometer using enriched isotopes of Eu¹⁵¹ and Eu¹⁵³, which have been excited in liquid air cooled hollow cathodes. From the measurements the values for the nuclear quadrupole moments

$$Q(Eu^{151} ) = (1.16 \pm 0.08) \cdot 10^{ - 24} cm^2 $$     

New neutron deficient isotopes with mass numbersA=136 and 145

High resolution laser-atomic-beam spectroscopy was applied to study crossed-second-order effects in the isotope shift of the terms 4f⁷5d6s a¹⁰D and a⁸D for¹⁵¹Eu-¹⁵³Eu. The term dependent effects lead to a difference in the isotope shift of the terms a¹⁰D and a⁸D of 415(20) MHz. The J dependent effects are interpreted through the use of one parameter z_5d for each term; z_5d(a¹⁰D)=41(7)MHz, z_5d(a⁸D)=50(26)MHz.     

151Eu Mössbauer studies on Eu1+x Ba2−x Cu3O7+δ oxide systems

Mössbauer parameters of¹⁵¹Eu in Eu_1+x Ba_2?x Cu₃O_7+δ have been studied as a function of temperature, forx=0.15 andx=0.25. The areas of the absorption spectra for the two samples are almost equal. This could mean that thef-Mössbauer factor for¹⁵¹Eu at the barium sites is much smaller than that for¹⁵¹Eu at the rare earth sites, i.e. we only observe the spectra of the latter sites. According to this, the fits of the spectra with a single quadrupolar pattern and with two quadrupolar patterns have given equivalent χ² values.