Anomalous shift in crossing frequency for the proton 1/2[541] band in175Ta

High-spin states in¹⁷⁵Ta have been populated in the¹⁶⁰Gd (¹⁹F,4n)¹⁷⁵Ta reaction with beams provided by the HI-13 tandem accelerator at the Institute of Atomic Energy in Beijing. A level scheme was constructed from γ-γ coincidence experiments. Seven decay sequences built on 5/2⁺[402], 1/2^?[541], 7/2⁺[404] and 9/2^? [514] proton Nilsson configuration have been extended to higher spin. An anomalously large delay of the neutron AB crossing built on the h_9/2 proton Nilsson State 1/2^?[541] is discussed.     

Description of the low-lying negative parity states in153Gd

To explain the properties of the recently observed negative parity states in the 89-neutron nucleus¹⁵³Gd, the Nilsson model is extended to include the Coriolis couplings between the 3^?/2 [521], 5^?/2 [523], 3^?/2 [532], 1^?/2 [530], 1^?/2 [510], 1^?/2 [521] and 5^?/2 [512] bands. The calculation reproduces rather well the experimental level energies, single neutron transfer cross sections and electromagnetic transition rates.     

Investigation of the158Eu decay

An activity of¹⁵⁸Eu was produced by an (n, p) reaction in an enriched gadolinium target by means of 14 MeV neutrons obtained from a SAMES generator. The gamma radiation accompanying the beta decay of¹⁵⁸Eu into¹⁵⁸Gd was detected by means of a Ge(Li) spectrometer. A 24-level decay scheme was devised and the transition probabilities were analyzed in terms of adiabatic theory and in terms of the theories including band mixing effects. The values of beta radiation intensities obtained from the experiment were compared with theoretical predictions calculated on the basis of the Nilsson model.     

New rotational bands in 174Ta

Three new bands in ¹⁷⁴Ta have been identified by using the ¹⁶⁰Gd(¹⁹F,5n) reaction at beam energies of 87 MeV and 96 MeV. Nilsson configurations are assigned to these bands. In the 9/2⁻[514]_p+5/2⁻[512]_n band, the AB neutron crossing occurs at a rotational frequency of 0.30 MeV. This is indicative of the disappearance of the evidence for a reduction in neutron pair correlations. Received: 30 March 1998     

Towards a shell-model description of the low-energy structure of deformed nuclei II. Electromagnetic properties of collective M1 bands

A shell-model theory, called the pseudo SU(3) model, which was proposed previously for giving the structure of low-lying states in heavy deformed nuclei is used to predict the number of 1⁺ states with strong M1 transitions to ground states for the nuclei ¹⁵⁴Sm, ^{156 160}Gd, ¹⁶⁴Dy, ¹⁶⁸Er, ¹⁷⁴Yb of the rare earth region and the actinide species ²³²Th, ^{234 240}U, ²⁴²Pu. Results are also given for E2 and M3 transition strengths in these nuclei. The measures provide a rigorous test of the theory, which in reality is a many-particle Nilsson scheme, because the real M1, E2, and M3 operators are used in the calculations. It is found that the results for E2 strengths using the real quadrupole operator differ by less than 5% from those of calculations that use the operator which is a generator of the pseudo SU(3) symmetry. This is so even for weak interband transitions. To further test the theory additional experimental information on the 2_γ⁺ states is necessary. In particular, the 1⁺ → 2_γ⁺ decay strengths are needed to differentiate between theories for the structure of the giant M1 states.     

Low-spin states of153Gd observed in the decay of153Tb

Level structure of the 89-neutron nucleus¹⁵³Gd has been investigated by studying theEC-decay of isotope-separated¹⁵³Tb sources with several semiconductor detectors. In addition to singles gamma and electron spectra,γ-γ ande ^?-γ coincidences were investigated by using Ge(Li) and Si(Li) spectrometers and a high-capacity two-parameter recording system. In all, 191γ-rays are assigned to the decay of the 2.4d¹⁵³Tb. The proposed level scheme of¹⁵³Gd containing most of the observed transitions shows a very high density of low-spin states (45 states below 1.5MeV). Spin and/or parity assignments based mainly on coincidence data and measured transition multipolarities are proposed for a majority of these states. Nilsson model classifications of some levels are discussed. On the basis of logf t values the spin and parity of the ground state of¹⁵³Tb are suggested to be 3/2⁺ or 5/2⁺.     

Tuning the bottleneck effect in Ag metallic host doped with magnetic Gd and non-magnetic Sb ions

The Ag metallic host doped with Gd and Sb is an excellent model system to study the bottleneck effect associated to the conduction-electron (c-e) spin-flip scattering mechanism. Electron spin resonance of Gd³⁺ in both, Ag-(Gd doped)- and Ag-(Gd and Sb doped)-systems, reveal the presence of bottleneck which can be tuned by the amount of Gd and Sb impurities. The increase of the Gd concentration leads to a c-e spin-flip relaxation rate to the magnetic Gd³⁺ ions larger than that to the lattice, favoring the bottleneck regime. Whereas the effect of the non-magnetic impurities (Sb ions) is to increase, via spin–orbit scattering, the spin-flip relaxation rate of the c-e to the lattice, weakening the bottleneck regime.     

N=28丰中子核的形变和形状共存研究

利用同位旋依赖的尼尔逊势,在宏观-微观理论框架下,计算了幻数N=28同中子链上原子核的性质,研究了N=28同中子链上原子核的形变和形状共存现象. 研究结果表明,N=28这个幻数在Na,Mg, Al同位素链上有着强的形状共存现象. 此外,计算表明⁴²Si的基态为扁椭球,同时在Si同位素链上的形状共存现象相对较弱. 关键词： 同位旋 幻数 形变 形状共存     

Rotational co-existence in selenium isotopes

High spin states of ^72,73,74Se nuclei are discussed using calculations from the cranked Nilsson Strutinsky method with tuning to fixed spins. The low spin anomaly in the yrast bands of these nuclei is interpreted in a rotational co-existence picture. High K rotational isomers are proposed for I ^π =4⁺ in ⁷²Se and 6⁺ in ⁷⁴Se.     

NMR-analysis of the conduction electron polarization at the gadolinium site in ferromagnetic intermetallic compounds

We have studied the zero field spin echo NMR of ¹⁵⁵Gd, ¹⁵⁷Gd, ¹³⁹La, ¹⁹¹Ir and ¹⁹³Ir in the compounds Gd_xLa_1-x Ir₂ and Gd_xY_1-xIr₂. The ¹³⁹La resonance in particular proved useful as probe for the contribution (H_N) of the hyperfine field at the Gd site in GdIr₂ which is due to the polarizing influence of all the other Gd moments in the lattice. In GdIr₂ the contribution H_N was found to be positive; it is due for about 56% to the four nearest neighbour atoms. The part of H_N coming from the second and third nearest neighbour atoms has the same sign (positive) as that of the nearest neighbours. We show how the varying magnitude and sign of H_N in intermetallic compounds of Gd can be used to estimate the relative importance of 5d electrons in the indirect coupling of the localized rare-earth moments.     

Observation of M3 isomeric transition from <Superscript>156m</Superscript>Pm through the βdecay of <Superscript>156</Superscript>Nd

An M3 transition in a doubly odd nucleus of ¹⁵⁶Pm was identified by internal conversion electron measurement through the β-decay of ¹⁵⁶Nd which was separated from the fission products of ²³⁵U using the on-line mass separator KUR-ISOL. The isomeric state at 150.3keV de-excites to the ground state with the M3 transition, and the spin-parity is considered to be 1^-. Nilsson configurations are also discussed on the basis of the systematics.     

Microstructural and magnetic properties of Ax:Zn1-xO (A=Mn,Gd and Mn/Gd) nanocrystals

We report the microstructural and magnetic properties of transition (3d) and rare earth (4f) metal substituted into the A_x:Zn_1?xO (A=Mn, Gd and Mn/Gd) nanocrystal samples synthesized by solgel method. The structural properties and morphology of all samples have been analysed using X-ray diffraction (XRD) method and scanning electron microscopy. The impurity phase in the XRD patterns for all samples is not seen, except (Mn/Gd):ZnO sample where a very weak secondary phase of Gd₂O₃ is observed. Due to the large mismatch of the ionic radii between Mn²⁺ and Gd³⁺ ions, the strain inside the matrix increases, unlike the crystallite size decreases with the substitution of Mn and Gd into ZnO system. A couple of additional vibration modes due to the dopant have been observed in Raman spectrum. The magnetic properties have been studied by vibrating sample magnetometer. The magnetic hysteresis shows that Mn:ZnO and Gd:ZnO have soft ferromagnetic (FM) behaviour, whereas (Mn/Gd):ZnO has strong FM behaviour at room temperature (RT). The enhancement of ferromagnetism (FM) in (Mn/Gd):ZnO sample might be related to short-range FM coupling between Mn²⁺ and Gd³⁺ ions via defects potential and/or strain-induced FM coupling due to the expansion lattice by doping. The experimental results indicate that RTFM can be achieved by co-substitution of 3d and 4f metals in ZnO which can be used in spintronics applications.     

The magnetic hyperfine field and the electric field gradient at181Ta impurities in Gd metal

The magnetic hyperfine fieldH _hf and the electric field gradientV _zz at¹⁸¹Ta impurties in metallic Gd were determined by time differential perturbed angular correlation measurements with the 133 keV K-conversion electron 482 keV -cascade of¹⁸¹Ta. The sources for these measurements were prepared by implantation of radioactive¹⁸¹Hf ions into Gd. The results are: |H _hf(TaGd; 77 K)|=285(14)kG, and |V _zz(TaGd; 330 K)|=5.32(15)·10¹⁷V/cm². The value ofH _hf fits well into the systematics for 5d impurities in Gd and indicates a positive core polarisation contribution, which is expected if the conduction electrons of Gd have to a large extent d-character. The electric field gradients of the 5d impurities in Gd are not consistent with a proportionality between the ionic and the electronic contribution.     

SU(3) coupling schemes for odd-odd nuclei in the interacting boson – fermion – fermion model with both odd proton and odd neutron in natural parity orbits

The SU^BFF(3) dynamical symmetry limits of interacting boson – fermion – fermion model are identified and they are appropriate for heavy deformed odd – odd nuclei for configurations with both the odd proton and odd neutron occupying all the natural parity orbits in the corresponding valence shells. There are three symmetry limits and their correspondence with two quasi-particle (proton-neutron) Nilsson configurations is established; one of the limits mixes both Nilsson n_z's and Λ's and other two limits mix only Nilsson Λ's. The ¹⁹¹Ir (d,t) ¹⁹⁰Ir single nucleon transfer spectroscopic strengths are well described by one of the symmetry limits that mixes only Nilsson Λ's. Received: 22 June 1998     

Multipole mixtures in gamma transitions in the (<Emphasis Type="Italic">n,n′γ</Emphasis>) reaction on <Superscript>160</Superscript>Gd

The spectrum of gamma rays from the reaction ¹⁶⁰Gd(n, n′γ) and their angular distribution with respect to the neutron-beam axis are measured by using fast reactor neutrons. The scheme of energy levels and gamma transitions is composed for ¹⁶⁰Gd. Multipole-mixture parameters δ are found for many gamma transitions.     

A microscopic explanation of the isotonic multiplet at N = 90 and of the F-spin multiplet in Dy-Hf

The N = 90 isotones of Nd, Sm, Gd and Dy, with almost similar deformed level structure and associated with X (5) symmetry, form the isotonic multiplet in Z = 50?C66, N = 82?C104 quadrant. This is explained microscopically in terms of the Nilsson level diagram. Using the Dynamic Pairing-Plus-Quadrupole model of Kumar-Baranger, the quadrupole deformation and the occupancies of the neutrons and protons in these nuclei in the Nilsson orbits have been calculated, which support the formation of N = 88, 90 isotonic multiplets. The existence of the F-spin multiplets, with almost identical spectra, recognized in earlier works, in Z = 66?C82, N = 82?C104 quadrant, is also explained microscopically in our study.     

Blocking of coupling to the 0<Subscript>2</Subscript><Superscript>+</Superscript> excitation in <Superscript>154</Superscript>Gd by the [505]11/2<Superscript>-</Superscript> neutron in <Superscript>155</Superscript>Gd

The concept that the first excited 0⁺ states in N = 90 nuclei are not a b \beta -vibration but a second vacuum formed by the combination of the quadrupole pairing force and the low density of oblate orbitals near the Fermi surface is supported by the blocking of this collective mode in ¹⁵⁴Gd from coupling to the [505]11/2^- single-particle quasi-neutron orbital in ¹⁵⁵Gd . The coupling of this orbital to the 2⁺ g \gamma -vibration in ¹⁵⁴Gd is observed since this coupling is not Pauli-blocked.     

Investigation of the hyperfine interaction of the transition element impurity193Ir in gadolinium

The combined magnetic and electric hyperfine interaction of dilute¹⁹³Ir impurities in ferromagnetic Gd has been investigated by means of the Mössbauer effect. The magnetic hyperfine field of¹⁹³Ir in Gd at 4.2 K is: |H _hf(Ir:Gd)|=624(6) kG.The electric fieldgradient at the site of Ir in Gd is:V _zz (Ir:Gd)=+19.5(5.0) × 10¹⁷ V/cm².The fieldgradient is axially asymmetric with an asymmetry parameter of 0.53(2)1.     

The electric field gradient for Gd in gadolinium metal

We have examined the temperture dependence of the efg for GdGd above the Curie point. Using anI =10⁺ isomer in¹⁴⁴Gd as a probe nucleus, we find a weakT ^3/2 dependence withB=(1.5±0.4) 10^–5 K^–3/2. The absolute value of the efg at 332 K was measured by Coulomb excitation of 2⁺ states in^{156, 158, 160}Gd, yielding |eq(332 K)|=(3.43±0.14) 10¹⁷ V/cm². A possible small deviation from theT ^3/2 temperature dependence of the efg for ferromagnetic Gd is discussed.     

Study of low-lying states in151Eu via (n,n′γ) reaction

The levels of¹⁵¹Eu have been investigated in the (n,n′γ) reaction using nuclear reactor fast neutrons. The energies, intensities and angular distributions of theγ-rays have been measured with the Ge(Li) spectrometer. Four rotational bands with the following band heads and Nilsson configurations have been identified: ground state band, 5/2⁺ [402]; 21.5 keV, 7/2⁺[404]; 196.5 keV, 3/2⁺[411]; 260.5 keV, 5/2⁺[413]. The low spin states at 332.2 and 336.2 keV have been tentatively assigned to the l/2⁺[411] Nilsson orbital, but 522.8, 580.0 and 587.0 keV states to the 1/2⁺[420] Nilsson orbital. The negative parity levels at 353.7, 522.1 and probably 546.2 keV have been proposed basing on theh _11/2 proton state.