Effective dynamic moment of inertia of 118Xe and 130Ba

The effective moment of inertia J_eff⁽²⁾ of ¹¹⁸Xe and ¹³⁰Ba has been measured using sum-spectrometer techniques. The data are discussed using arguments based on particle alignments and results of cranking calculations. J_band⁽²⁾ and J_eff⁽²⁾ are compared in order to estimate the contribution of particle alignments to the total increase in angular momentum.     

Rotational properties of the odd-Z transfermium nucleus 255Lr by a particle-number-conserving method in the cranked shell model

Experimentally observed ground state band based on the 1/2-[521] Nilsson state and the first exited band based on the 7/2-[514]Nilsson state of the odd-Z nucleus ~(255)Lr are studied by the cranked shell model(CSM) with the paring correlations treated by the particle-number-conserving(PNC) method. This is the first time the detailed theoretical investigations are performed on these rotational bands. Both experimental kinematic and dynamic moments of inertia(J~(1)and J~(2)) versus rotational frequency are reproduced quite well by the PNC-CSM calculations. By comparing the theoretical kinematic moment of inertia J~(1) with the experimental ones extracted from different spin assignments, the spin 17/2~-→13/2~- is assigned to the lowest-lying 196.6(5) ke V transition of the 1/2~-[521] band, and 15/2~-→11/2~- to the 189(1) ke V transition of the 7/2~-[514] band, respectively. The proton N = 7 major shell is included in the calculations. The intruder of the high- j low-? 1 j_((15)/2)(1/2~-[770]) orbital at the high spin leads to band-crossings at ω≈0.20( ω≈0.25) Me V for the 7/2~-[514] α =-1/2(α = +1/2) band, and at ω≈0.175 Me V for the1/2~-[521] α =-1/2 band, respectively. Further investigations show that the band-crossing frequencies are quadrupole deformation dependent.     

Effects of quantum fluctuations on electromagnetic properties in triaxial nuclei

Effects of quantum fluctuations, like wobbling and γ-fluctuations, are examined in even- as well as in odd-particle systems by making use of a simple model based on the Bohr hamiltonian. The strong signature dependence observed in ΔI = 1 E2 transitions in odd nuclei is studied in the context of an axially asymmetric deformation. We point out the importance of the quantum fluctuations especially at low-spin values and / or for shapes with small deviations from axial symmetry. It is also demonstrated that the J⁽²⁾ moment of inertia may be larger than J⁽¹⁾ due to the wobbling motion.     

Depolarizing collisions in ytterbium vapor: Isotropic and anisotropic relaxation

Isotropic depolarizing collisions are studied using a stimulated photon echo with a specific polarization of the excitation radiation pulses in a mixture of ytterbium with krypton for the J = 1 ? J = 0 transition of ¹⁷⁴Yb. The difference between the relaxation rates of orientation and alignment γ _b ⁽²⁾ ? γ _b ⁽¹⁾ of the ³ P ₁(6s6p) ¹⁷⁴Yb level is measured as a function of the krypton pressure. The collision photon echo at the J = 1 ? J = 0 transition induced by the anisotropic relaxation is studied for the Yb + Xe mixture. The power of the collision echo increases from zero with the addition of a buffer gas to ytterbium, reaches an optimal level, and decreases with an increase in the buffer gas pressure. The polarization of this collision-induced echo differs from the polarization of the conventional echo. The experimental results are in qualitative agreement with theoretical predictions.     

Measurement of g-factors in 170Yb, 172Yb and 174Yb by transient field interaction at high recoil velocities

A beam of ⁴⁰Ca ions at 168 MeV has been used to Coulomb excite high-spin states in ¹⁶⁹Tm and ^{170, 172, 174}Yb which recoiled through thin polarized iron at ν/c ≈ 3.5%. An enhanced transient field ≈ 6 times larger than the Lindhard-Winther prediction was observed and calibrated against the known g-factors in ¹⁶⁹Tm. Individual g-factors could not be extracted because of strong feeding; nevertheless, deviations from rotational behaviour (constant g-factors) would be detectable. Empirical fits to microscopic calculations of the rotational g-factors below spin 12⁺ suggest that if deviations from the simple rotational formula occur, they should be of the form g(J) = g₀(1 + αJ²). We find the following values in ^{170, 172, 174}Yb: α × 10³ = ?0.5±1.5, +1.0±1.5. The uncertainties are the level at which deviations from rotational behaviour are expected to occur. The results are discussed in terms of Coriolis anti-pairing effects.     

Measurement of Δ1J(199Hg, 31P) in [HgPCy3(OAc)2]2 and relativistic ZORA DFT investigations of mercury–phosphorus coupling tensors

Using ³¹P solid-state NMR spectroscopy, anisotropy in the indirect ¹⁹⁹Hg-³¹P spin–spin coupling tensor (ΔJ) for powdered [HgPCy₃(OAc)₂]₂ (1) has been measured as 4700±300 Hz. Zeroth-order regular approximation (ZORA) density functional theory (DFT) calculations, including scalar and spin-orbit relativistic effects, performed on 1 and a series of other related compounds show that ΔJ(¹⁹⁹Hg, ³¹P) arises entirely from the ZORA Fermi-contact–spin-dipolar cross term. The calculations validate assumptions made in the spectral analysis of 1 and in previous determinations of ΔJ in powder samples, namely that J is axially symmetric and shares its principal axis system with the direct dipolar coupling tensor (D). Agreement between experiment and theory for various ¹⁹⁹Hg, ³¹P spin–spin coupling anisotropies is reasonable; however, experimental values of ¹J(¹⁹⁹Hg, ³¹P)_iso are significantly underestimated by the calculations. The most important improvements in the agreement were obtained as a result of including more of the crystal lattice in the model used for the calculations, e.g., a change of 43% was noted for ¹J(¹⁹⁹Hg, ³¹P)_iso in [HgPPh₃(NO₃)₂]₂ depending on whether the two or three nearest nitrate ions are included in the model. Finally, we have written a computer program to simulate the effects of non-axial symmetry in J and of non-coincidence of the J and D on powder NMR spectra. Simulations clearly show that both of these effects have a pronounced impact on the ³¹P NMR spectrum of ¹⁹⁹Hg–³¹P spin pairs, suggesting that the effects should be observable experimentally if a suitable compound can be identified.     

Study of 170,171,173Ta isotopes at high spinṡ

High-spin data are presented for ¹⁷⁰Ta and ¹⁷¹Ta for the first time, and the known level scheme of ¹⁷³Ta is extended to higher spins. Anomalies found in the crossing frequencies for the alignment of a pair of neutrons are considered. At high spin a large and constant value of J⁽²⁾, with J⁽²⁾ > J⁽¹⁾, is found for two ¹⁷¹Ta bands and the implications of this are discussed. The πi_13/2 [660]1/2⁺, α = + 1/2 orbital is identified as it crosses the rotational band built on the [402]5/2⁺, α = + 1/2 orbital in ¹⁷¹Ta. Magnetic transition probabilities obtained from measured branching ratios show the effects of the aligning pair of neutrons and the spectator orbital. The data are interpreted using cranked shell-model calculations and a semiclassical vector-coupling scheme developed by Donau and Frauendorf.     

Properties of rotational excitations in odd mass Dy isotopes

The data on high-spin rotational states in¹⁵⁵Dy,¹⁵⁷Dy,¹⁵⁹Dy and¹⁶¹Dy are discussed within a model where a particle is coupled to a rotor with a variable moment of inertia. In this model there is often a definite improvement in the quality and stability of the fits to levels in the positive-parity band below spin 25/2 when the moment of inertia of the core exhibits a linear dependence on the square of the rotational angular velocity as compared to the situation where a linear dependence onI(I+1) is assumed. In the improved fits the empirical matrix elements of the Coriolis force exhibit a smooth and significant increase with decreasing moment of inertia. The rotational energies above spin 25/2 in the positive-parity band and above 19/2 in the 11/2^? [505] band are understood within the present theoretical model if the moment of inertia increases more rapidly than the linear trend established at lower spin. In the 11/2^? [505] band this increase follows rather closely the behaviour in the even nuclei whereas in the positive-parity band the curves are quite flat even beyond the point where the moment of inertia in the even nuclei exhibits a discontinuous or back-bending behaviour. The significance of this observation is discussed in the light of existing theories on nuclear moments of inertia.     

Level-Crossing-Untersuching der Stark-Aufspaltung der tiefsten1 P 1-Terme von Ca,Sr und Ba

Using the level-crossing technique, magnitude and sign of the tensor polarizability α_ten of the lowest¹ P ₁-levels of Ca, Sr, and Ba have been measured by investigating the splitting into Zeeman-sublevels in superimposed homogeneous electric and magnetic fields. The experimental results are: α_ten/g _J =?13.6(3) kHz/(kV/cm)² for Ca α_ten/g _J =?14.32(15) kHz/(kV/cm)² for Sr α_ten/g _J =?10.72(10) kHz/(kV/cm)² for Ba, where theg _J -values are approximatelyg _J≈1. With greater accuracy the ratios of these constants have been determined by eliminating the electric-field strength measurement: (α_ten(Sr)/g _J (Sr))/(α_ten(Ca)/g _J (Ca))=1.050(8) (α_ten(Sr)/g _J (Sr))/(α_ten(Ba)/g _J (Ba))=1.336(2). The polarizability constants are discussed with regard to the state vectors of the lowestsp ¹ P ₁- and³ P ₁-levels. The tensor polarizability of the 6s 6p¹ P ₁-level of Ba I is considered in relation to oscillator strengths of electric dipole transitions to neighbouring levels.     

Investigation of high spin states in23Na and23Mg and the12C+12C resonance atE c.m.=19.3 MeV

The resonance in the¹²C+¹²C system atE _c.m.=19.3 MeV has been studied in the neutron and proton decay channels. From(p, γ), (n, p) and (n, γ) coincidence measurements high spin states could be localized inA=23 nuclei, in²³Mg up to possibly 21/2⁺. These states were resonantly populated. The present data favorJ ^π=17/2⁺ for the 9.61 MeV state in²³Mg and therefore also for the probable parent state at 9.81 MeV in²³Na. AJ ^π=12⁺ assignment to the resonance is supported and evidence was found that the resonant excitation of the lowest 15/2⁺ and 17/2⁺ states in mass 23 nuclei is caused by a change of the intrinsic structure of the Yrast levels aroundJ ^π=15/2⁺ towards larger deformation.     

A superdeformed band in131Ce

A rotational band of 16γ-rays has been found in¹³¹Ce with a high moment of inertia indicating a deformation ε₂～0.38 and extending to spin ～40?. Its intensity is ～～5% of the total in¹³¹Ce, confirming a difference in the intensity systematics for superdeformed states in Ce nuclei compared with Nd.     

Indirect carbon–carbon spin–spin couplings across one,two and three bonds in pyridine and diazine systems: experiment and theory

An excellent linear correlation is found between a large body of experimental spin–spin carbon–carbon couplings, J(CC), across one, two and three bonds in pyridine and diazine ring systems and the corresponding B3PW91/6‐311++G(d,p)//B3PW91/6‐311++G(d,p) computations. The correlation does not differ significantly from the simplest relationship possible, J(CC)_exp. = J(CC)_calcd., within a small and random spread of about 1 Hz. There are 276 experimental values considered, and 124 out of these are new and come from the present work. The aromatic carbon–carbon couplings vary from ?7.6 through +78.5 Hz. It is shown that the correlation provides a reliable tool for predictions of the signs of aromatic J(CC)'s even if the magnitudes of the latter are of the order of 1 Hz. It is demonstrated, for the first time, that the relatively weak ² J(CC) couplings, in the heteroaromatic systems studied, can bear either sign and span a considerable range of about 11 Hz. The character of the correlation indicates that rovibronic effects on aromatic J(CC)'s and those of nuclear motions on aromatic J(CC)'s are practically negligible. All of this is in a perfect agreement with our recent extensive studies on aromatic J(CC)'s in analogous benzene ring system. Substituent effects on the aromatic J(CC)'s turn out to be significant not only for ¹J(CC)'s but also for most of ³J(CC)'s and ² J(CC)'s, and the computation neatly reciprocates these trends. Copyright © 2008 John Wiley & Sons, Ltd.     

Magnetism,spin relaxation and hyperfine interactions of rare earths in RM6Al6(M = Cr,Mn, Cu)

The systems RM₆Al₆ (R = rare earth or Y, M = Cr, Mn, Cu, Rh) were studied by magnetization measurements and by Mossbauer spectroscopy of ¹⁵⁵Gd, ¹⁶¹Dy, ¹⁶⁶Er and ¹⁷⁰Yb. The magnetization studies show weak R-R antiferromagnetic exchange interactions in RCu₆Al₆(T_n)Gd) = 21 K, less than 4 K for all other R and strong crystalline field effects. Similar phenomena are observed in RMn₆Al₆ and RCr₆Al₆, however, due to the presence of a Mn or Cr local moment the systems order ferrimagnetically. In RCr₆Al₆the order temperatures are low T_c ～ 25 K, yet T_c(GdCr₆Al₆) = 170 K. The Mossbauer studies observations are consistent with the magnetiza results. In the case where Er and Yb are not ordered at 4.1 K, the spectra still show magnetic hyperfine structure however of paramagnetic nature. The spectra yield the hyperfine interaction spin Hamiltonian parameters and the spin relaxation rates. These turn out to be extremely slow (1O⁸–1O⁹ sec^?1, a very uncommon phenomenon for a concentrated Er or Yb metallic system.     

Richtungskorrelationsuntersuchungen an den γ-Kaskaden des131Cs

The¹³¹Cs decay has been studied by angular correlation measurements of the (404-216), (832-216), and (247-373) keV γ-cascades using NaJ(Tl)-detectors in connection with a two parameter multi-channel analyzer. Unique spin assignments are obtained for the 216 (Jπ=3/2⁺) and 373 (Jπ=3/2⁺) keV levels. A previously discussed value ofJπ=5/2⁺ for the 1048 keV level is ruled out. The multipole character of the 404 keV transition is found to beE2 with less than 2%M1.     

Supplementary data concerning the58Ni(p,p′ γ) reaction

Angular correlation measurements for the⁵⁸Ni(p, p′ γ) reaction were performed atE _p =8.1 MeV. Method II of Litherland and Ferguson was used to determine multipole mixing ratios of the γ-radiation and spins of most of the excited levels up to 4.11 MeV. The results confirm for the most part recent measurements of van Patteret al.; the 2775 keV state was verified to have a spin ofJ=2. Several discrepancies and additional information concerning the 3531, 3774, 3898 and 4108 keV levels are discussed. A spin value ofJ=1 is assigned to the 3531 keV level, clearly ruling out former assignments of 4⁺ and 0⁺. AJ=4 assignment is proposed for the 3774 keV state, contrary to the generally assumed value ofJ=3, which these measurements do not support.     

On the cause for the no spin-gap behavior of the triangular spin tube system CsCrF4

The spin exchange interactions of the triangular spin tube system CsCrF₄ were evaluated by performing mapping analysis on the basis of density functional theory calculations. Our results show that the exchange J₁ for the triangular ring and the exchange J₂ along the chain are both antiferromagnetic with the ratio J₁/J₂≈0.5, so the spin gap of CsCrF₄ is too small to be experimentally detected. This finding is consistent with the experimental observation and theoretical analysis. The possible ways of preparing a triangular spin tube with observable spin gap was discussed.     

Experimental study of high spin states in the ground state bands of158,160Er,164,166Yb,and168Hf

Ground state rotational bands in the deformed doubly-even rare earth nuclei^158,160Er,^164,166Yb, and¹⁶⁸Hf have been observed in (α, 8n γ) reactions. The γ-spectra associated with these reactions were studied in-beam using conventional spectroscopic methods. In all five nuclei the nuclear moment of inertia of the ground state rotational states was found to increase abruptly as higher spin states were attained. In a plot of the moment of inertia as a function of the angular velocity all these five nuclei display “backbending” curves. Moreover, in¹⁵⁸Er and¹⁶⁶Yb, the curves after passing through a maximum bend subsequently downwards.     

Evaluation of exchange interaction in binuclear copper(II) chelates of amide-based cyclophanes

Temperature dependence of the electron paramagnetic resonance (EPR) spectra of binuclear Cu(II) complexes with amide-based cyclophanes, Cu₂(bis-EDTAPDN), Cu₂(bis-EDTANAP) and Cu₂(bis-EDTABPE), in 60% methanol (pH ca. 10) has been studied at a frequency of 9.43 GHz in the temperature range of 77–4.2 K; the cyclophanes are macrocyclic compounds in which four amide bonds link two ethylenediaminetetraacetate (EDTA) units and two units of the aromatic diamine 1,4-phenylenediamine (DPN), 1,5-diaminonaphthalene (NAP) or bis(4-aminophenyl) ether (BPE). Exchange integrals found from the EPR measurements are ca. 70–105 cm^?1, 22 cm^?1 andJ ≤ 0, for Cu₂(bis-EDTAPDN), Cu₂(bis-EDTANAP) and Cu₂(bis-EDTABPE), respectively; the sign ofJ is defined to be positive for antiferromagnetic interaction. The variation of exchange interactions in these compounds is related to the nature of the bridging organic groups.