Precise Quadrupole Moment of the Doubly Closed Shell Plus One Proton Nucleus 41Sc

In order to precisely determine the |eqQ(⁴¹Sc)/h| of ⁴¹Sc(I ^π=7/2⁻, T _1/2=0.596 s) implanted in a TiO₂ single crystal the electric field gradient tensor and anisotropic chemical shift were determined by detecting the Fourier Transformed Pulse-NMR of ⁴⁵Sc(I ^π=7/2⁻, stable) in the crystal at a high field of 7.0 T and 9.4 T. Combining the new |eqQ(⁴¹Sc)/h| value with the Q(⁴⁵Sc)=−(23.6±0.2) fm², also renewed by using the known atomic hyperfine interaction constants and Sternheimer polarization effect, the |Q(⁴¹Sc;I ^π=7/2⁻,T _1/2=0.596 s)|=(15.6±0.3) fm² has been precisely determined. The value is compared with the theoretical Q(⁴¹Sc) given by a shell model code. This revised version was published online in September 2006 with corrections to the Cover Date.     

Hyperfine Interactions of 8Li in Ferromagnetic Single Crystal Fe

The hyperfine interactions of ⁸Li implanted in single crystal Fe have been studied using the β-NMR technique. One kind of hyperfine field B _hf was found. Since no dipolar field was observed, ⁸Li nuclei are suggested to sit in substitutional sites. The B _hf and the spin-lattice relaxation time T ₁ were observed as functions of temperature. The experimental B _hf and T ₁ were compared with the theoretical predictions from the first principles KKR-band-structure calculations. While predicted B _hf for the substitutional site is consistent with the experiment, predicted T ₁ cannot reproduce the experiment well. This revised version was published online in September 2006 with corrections to the Cover Date.     

Hyperfine Interactions of 12B in CaB6

The hyperfine interactions of short-lived β-emitter ¹²B implanted into a CaB₆ crystal have been studied by means of the β-NMR technique. An electric quadrupole splitting has been observed at room temperature from which an electric field gradient of q=−(1.34±0.05)×10²¹ V/m² was determined. From the present result, it was found that the ¹²B nuclei are mainly implanted in the substitutional boron site. This revised version was published online in September 2006 with corrections to the Cover Date.     

Lattice Locations of 8Li and 12N in Al

The line widths of the β-NMR spectra of the short-lived β emitters ⁸Li and ¹²N implanted in a single crystal of Al have been measured precisely for the first time as a function of crystal orientation. The NMR line widths were compared with the theoretical van Vleck values of the dipolar broadening. As a result, it was found that ⁸Li mainly sits in substitutional sites, while ¹²N sits in tetrahedral interstitial sites, in Al. This revised version was published online in September 2006 with corrections to the Cover Date.     

Quadrupole Moments of Na Isotopes

The electric quadrupole coupling constants eqQ/h of ²⁰Na (I ^π = 2⁺, T _1/2 = 449.7 ms), ²¹Na (I ^π = 3/2, T _1/2 = 22.49 s) and ²⁵Na (I ^π = 5/2, T _1/2 = 59.6 s) in single crystal ZnO and TiO₂ were precisely measured by applying the β-NMR technique. The ratio of the quadrupole moments between ²⁰Na (²⁵Na) and ²¹Na was determined to be 0.728 ± 0.023 (0.011 ± 0.002).     

Hyperfine Interactions of Short-Lived β Emitters in Pd

The Knight shifts K and the spin-lattice relaxation time T ₁ for the short-lived β-emitters ¹²B and ¹²N implanted into Pd have been measured by means of the β-NMR method. The results show that K depends on temperature. The obtained values of experimental K were compared with theoretical values derived with the KKR method.     

A Possible Nuclear Spin Dewar. Hyperfine Interactions of Short-Lived β Emitter 8Li and 12B in TiO2

It was confirmed by detecting the β-NMR of ¹²B (I ^π=1⁺, T _1/2=20.2 ms) in a TiO₂ (rutile) crystal that the nuclear spin polarization of ¹²B was totally maintained in the crystal as produced through a nuclear reaction before implantation. Two locations, site 1 and site 2, were found with the relative populations 9 and 1, respectively, and the electric field gradients (EFGs) at those sites were obtained to be q(site 1)=+(37.1±0.5)10¹⁵ V/cm², η(site 1)<0.03, q(site 2)=+(185±5)10¹⁵ V/cm² and η(site 2)=0.62±0.02. We also found that about 30% of the initial polarization of ⁸Li (I ^π=2⁺, T _1/2=838 ms) was maintained in the crystal. Since the polarizations of other β emitting nuclei, ^12,16N, ^13,19O, and ⁴¹Sc were also totally maintained in the crystal, the crystal can be a “Spin Dewar” in which many short-lived nuclides can be implanted with their polarizations totally maintained during their lifetimes for the studies not only on the electronic structure of impurities in it but also on the nuclear properties. This revised version was published online in September 2006 with corrections to the Cover Date.     

Hyperfine Fields of Sr and Y in Ferromagnetic Hosts, and Magnetic Moment of 93Y

Recent studies of hyperfine fields B _HF of Sr and Y in Fe are briefly reviewed. The B _HF value of Y in Ni is given by NMRON of ^91mYNi. The nuclear magnetic moment of the ground state of ⁹³Y is extracted from the β-ray detected NMRON of ⁹³YFe.     

Hyperfine Interactions in CeT2Ge2 (T = Mn,Co) Heavy Fermions Compounds Measured by TDPAC

Time Differential Perturbed γ–γ Angular Correlation (TDPAC) technique was used to measure the magnetic hyperfine field at both Ge and Ce sites in CeMn₂Ge₂ and CeCo₂Ge₂ intermetallic compounds. The ¹¹¹In (¹¹¹Cd) probe nuclei was used to investigate the hyperfine interaction at Ge sites, while the ¹⁴⁰La (¹⁴⁰Ce) nuclei was used to measure the magnetic hyperfine field at Ce site. The present measurements cover the temperature ranges from 10–460 K for CeMn₂Ge₂ and 9–295 K for CeCo₂Ge₂, respectively. The result for ¹¹¹Cd probe showed two distinct electric quadrupole frequencies above magnetic transition temperatures, in both compounds and a combined interaction in the magnetic region. The temperature dependence of the magnetic hyperfine field at ¹¹¹Cd at Mn site for the CeMn₂Ge₂ compound showed a transition from ferromagnetic to antiferromagnetic phase around 320 K and from antiferromagnetic to paramagnetic phase at 420 K. While a small magnetic field was measured on ¹¹¹Cd at Co site, no magnetic field on ¹⁴⁰Ce site was observed in CeCo₂Ge₂. This revised version was published online in September 2006 with corrections to the Cover Date.     

Hyperfine Interactions at 181Ta in Hf2Co7

In this paper we report a time differential perturbed angular correlation (TDPAC) study of hyperfine interactions at ¹⁸¹Ta in Hf₂Co₇ compound. The TDPAC measurements have been performed in the temperature range 77–1023K. The measured spectra showed broad distribution of hyperfine interactions up to 388K. Above this temperature, in a reversible manner, two nuclear electric quadrupole interactions (EQI) have been observed: at 393K, _Q1=449.0(27)MHz, ₁=0.00(4) and _Q2=144.7(41)MHz, ₂=0.44(2). Since the Curie temperature for this compound is known from the literature to be around 420K, only magnetic order transition could be responsible for such an observation. However, the measurements of magnetization did not exhibit any drastic change in this temperature range.     

Behavior of Boron Implanted in Semiconductor Si

Using β-NMR with ¹²B nuclei the temperature dependence of the lattice locations of boron implanted in Si is studied. At low temperature almost 100% of the implanted B is in either substitutional site or nonsubstitutional site. Above 260 K, the nonsubstitutional B rapidly becomes undetectable and disappears at a temperature higher than 325 K due to the fast spin-lattice relaxation. Above 450 K, the fraction of substitutional B increases to 100%. These experimental results are consistently explained by the thermal atomic jump and the dissociation of the defect associated with the nonsubstitutional B. This revised version was published online in September 2006 with corrections to the Cover Date.     

Quadrupole interaction of tantalum impurities in bismuth metal

The time differential perturbed angular correlation technique has been used in the measurement of the electric quadrupole interaction of Ta impuritiy in bismuth metal. The interaction frequencies at 293, 400 and 500 K have been observed to be 288±1.5, 266.9±3 and 244.5±4.3 MHz respectively. The electric field gradient at 293 K is 4.75±0.3 × 10¹⁷ V/cm² with the temperature coefficientB=2.2±0.2 × 10⁻⁵ (K)^−3/2.     

Measurement of Quadrupole Interactions in LaMO3 (M = Cr,Fe, Co) Perovskites by TDPAC

The perturbed angular correlation (PAC) technique has been used to study the electric field gradient (EFG) in LaCoO₃ perovskite. The results are compared with those for LaCrO₃, LaFeO₃ measured earlier. The PAC probe, ¹¹¹In → ¹¹¹Cd, was introduced in the oxide lattice by means of chemical reaction during sample preparation. In the present work, the temperature dependence of the electric quadrupole interaction parameters, for LaCoO₃ was investigated. The resulting systematics of EFG at ¹¹¹Cd, in La(Cr,Fe,Co)O₃ perovskites, reveals a linear dependence with temperature. This revised version was published online in September 2006 with corrections to the Cover Date.     

Investigations on the Diffusion of Boron in SiGe Mixed Crystals

By studying the quadrupolar interaction of ¹²B in silicon–germanium mixed crystals with the β-NMR method, the boron–germanium pair was identified and the saturation amplitudes for boron in differently composed crystals were measured. The relative saturation amplitudes agree with statistical predictions. At low temperatures boron is preferentially implanted into stable interstitial sites. These sites are converted into substitutional sites by diffusion processes which take advantage of reorientation jumps.     

Electric Field Gradients of B in TiO2

We observed the electric quadrupole interaction of ¹²B implanted in the interstitial site of TiO₂ using β-NMR method. The electric field gradients including the direction of the principal axes were determined. The direction agreed well with the theoretical calculation.     

Investigation of Hyperfine Interactions in CeIn3 byTDPAC

Magnetic hyperfine fields (mhf) at ¹¹¹Cd and ¹⁴⁰Ce nuclei, dilutely substituting the In and Ce sites, respectively, have been measured in the intermetallic compound CeIn₃ using perturbed angular correlation technique. A pure electric quadrupole interaction with an axially symmetric electric field gradient was observed at ¹¹¹In(EC)¹¹¹Cd probe nuclei at room temperature while a combined magnetic dipole and electric quadrupole interaction is observed below 10K. Below the ordering temperature, only a magnetic interaction is observed at ¹⁴⁰La(^–)¹⁴⁰Ce probe. The values of mhf measured experimentally as a function of temperature are discussed in terms of critical behavior.     

Nuclear Spin Orientation Created in Heavy Ion Collisions and the Sign of the Q Moment of 13B

The momentum dependences of the nuclear spin polarization P and alignment A of ¹³B(, T _1/2 = 17.36 ms) produced in the 100A MeV ¹⁵N + Be collisions have been measured by detecting β-ray asymmetry. Because both the P and A were significantly smaller than the prediction from a simple kinematical model, some relaxation mechanisms must be take into account. Comparing the signs of the observed alignment of ¹²B, the sign of the quadrupole coupling constant eqQ of ¹³B in TiO₂ was determined to be positive.     

Nuclear Spin Alignment of 12,13B Produced in Heavy Ion Collisions

The nuclear spin alignments of the β-emitting fragments ¹²B(I ^π=1⁺, T _1/2=20.2 ms) and ¹³B(I ^π=3/2⁻, T _1/2=17.4 ms) produced in the 100A-MeV ¹³C, ¹⁵N + ⁹Be collisions respectively have been observed for the first time detecting asymmetric β-ray emission from these nuclei. By means of the spin manipulation technique based on the hyperfine interaction of B isotopes in TiO₂, both the polarization P and the alignment A were determined reliably. The obtained P and A were significantly smaller than the expectation from the kinematical model. From the fact that the quenching factors for P and A are almost the same, there may be some depolarization mechanism in the collision process itself. This revised version was published online in September 2006 with corrections to the Cover Date.     

Perturbed Angular Correlation Study of Magnetic and Electric Hyperfine Interactions at 111Cd in GdNi2 and SmNi2

The magnetic hyperfine field B _hf of the closed-shell probe nucleus ¹¹¹Cd in the C15 Laves phase RNi₂ (R= Gd, Sm) has been investigated as a function of temperature by perturbed angular correlation (PAC) spectroscopy. The saturation magnetic hyperfine fields at 10 K are B _hf=7.7(2) and 3.9(1) T for GdNi₂ and SmNi₂, respectively. Although the probe nucleus resides on the cubic rare-earth site, a strong axially symmetric electric quadrupole interaction (QI) is observed in the paramagnetic phase at T300 K. The possible relation of this unexpected QI to the structural instability of RNi₂ is discussed.     

Hyperfine Interactions of 181Ta in Zr2Ni Observed Using PAC Spectroscopy

We have measured nuclear electric–quadrupole interactions (EQI) at ¹⁸¹Ta impurities substituted as Hf atoms into the Zr site in Zr₂Ni. Using perturbed-angular-correlation (PAC) spectroscopy, we measured the EQI over temperatures ranging from 10 to 1200 K. Over the entire range of temperature, the Zr₂Ni crystal has a bct Al₂Cu structure that includes a single Zr site. The crystal field symmetry surrounding this site is rather low, giving rise to a highly asymmetric electric-field gradient tensor. At 10 K, the EQI is characterized by an angular frequency ω₀=601(3) Mrad s⁻¹, and an asymmetry parameter η=0.835(2). At 1200 K, ω₀ decreases to 516(3) Mrad s⁻¹, and η also decreases to 0.790(4). Although weak, the temperature dependence of ω₀ is consistent with a (1−BT ^3/2) power law, in which B=6×10⁻⁶ K^−3/2. The EQI also manifests a very narrow linewidth. We observed no evidence either for magnetic ordering or for structural phase transitions in the temperature range covered by this experiment. Moreover, the sharpness of the EQI indicates that the samples as prepared are remarkably free of strain and defects. These results indicate that the Zr₂Ni structure does not promote the formation of defects and that the power-law dependence of ω₀ on T is insensitive to the asymmetric nature of the crystal. This revised version was published online in September 2006 with corrections to the Cover Date.