Hyperfine interaction of Ce and La in 3-d ferromagnets

NMR/ON measurements on¹⁴¹CeFe show the sign of the hyperfine field of CeFe to be negative. For the¹⁴¹Ce nucleus a g-factor of ¦g_N¦=0.311±0.011 is found. With this g-value a hyperfine field of H_hf=?41±2 T for CeFe is derived. Low temperature nuclear orientation experiments on¹⁴¹CeCo and¹⁴⁰LaFe yield ¦H_hf¦=30±3 T and ¦H_hf¦=46±5 T respectively. The valence of cerium impurities in Fe, Co and Ni is discussed.     

Hyperfine fields in the 5sp series studied by the low temperature nuclear orientation of83Rb,83Sr,85Sr and85Ym in iron

The hyperfine fields B_hf (RbFe), B_hf (SrFe) and B_hf (YFe) have been determined by the low temperature nuclear orientation of dilute samples of⁸³Rb,^83,85Sr and⁸⁵Y^m in an iron lattice to be B_hf (RbFe)=+54 (10) kG, B_hf (SrFe)=(?)100 (30) kG and B_hf (YFe)=?226 (10) kG. These results are compared with recent calculations for these fields (1), (2).     

Nuclear orientation and resonance studies of96TcFe

Low temperature nuclear orientation and nuclear magnetic resonance (NMRON) have been used to measure the magnetic hyperfine interaction in⁹⁶TcFe and the decay scheme properties of⁹⁶Tc. The spin of the⁹⁶Tc ground state is confirmed as 7. Its magnetic moment μ(⁹⁶Tc)=5.37±0.17 n.m. The magnetic hyperfine field for⁹⁶TcFe is ?298±10 kOe. The anisotropies of the 778, 813, 850 and 1126 keV transitions in⁹⁶Mo agree with pure E2 multipolarity assignments. The spin-parity of the 2876 keV level is 7⁺.     

Measurement of theg-factor of the 21 + state of192Pt in an external magnetic field

Theg-factor of the 2₁ ⁺ state of¹⁹²Pt has been measured by the IPAC technique in an external magnetic field as:g(2₁ ⁺,¹⁹²Pt)=+0.287(17). An additional IPAC experiment with an¹⁹²IrFe sample was performed with the same level in order to investigate the hyperfine field. The result:ω _L τ(2₁ ⁺,¹⁹²PtFe)=0.1115(9) gives the hyperfine field:B _hf ^4.2k (PtFe)=126.8(71) T. The result of an LTNO experiment with the same level is compatible with the assumption that 100% of the¹⁹²Ir atoms were on unique sites.     

Core vibration of99Tc

The gyromagnetic ratios and the half-lifes of the 141 keV and 181 keV states of⁹⁹Tc have been remeasured. The results,g(141 keV)=+1.280(44);g(181 keV)=+1.446(20) andT _1/2(141 keV)=0.205(4)ns;T _1/2(181 keV)=3.44(3) ns are in only fair agreement with prior published data but more precise. They confirm that both states are members of the ground state core vibration multiplet. The hyperfine field of TcFe has been determined asB _hf ^10K (TcFe)=30.42 (30)T;B _hf ^290K (TcFe)=29.47 (29)T     

Untersuchung von Kernniveaus des16O bis 14 MeV Anregungsenergie durch unelastische Elektronenstreuung

Using electrons with up to 60 MeV energy, ten transitions in¹⁶O have been studied: twoE0 (6.05 and 12.05 MeV), oneE1 (13.10 MeV), fourE2 (6.92, 9.85, 11.52 and 13.1 MeV), twoM2 (12.53 and 12.96 MeV) and oneE3 (6.13 MeV). The cross sections measured as a function of momentum transfer have been analyzed to yield transition probabilities to the ground state and transition radii. The results are compared with the theory ofBrown andGreen, and with the particle-hole calculations ofLewis andDeForest. For levels at 11.08 and 13.67 MeV, upper limits for the transition probabilities are given.     

Nuclear magnetic resonance on oriented192Ir in Fe and Ni

The hyperfine interaction of¹⁹²Ir nuclei as dilute impurities in Fe and Ni has been investigated with NMR on oriented nuclei. With the use of highly dilute and pure alloys the line widths could be reduced so far that the quadrupole splitting of¹⁹²IrFe and¹⁹²IrNi could be resolved. Taking hyperfine anomalies into account the ground state nuclear moments of¹⁹²Ir are deduced as |μ|=1.924(10)μ _N andQ=2.36(ll) b. The hyperfine field of IrNi was investigated as a function of the Ir concentrationc between 0.01 at % and 5 at %. The dependence ofH _HF onc was found to be significantly smaller than that reported from Mössbauer effect measurements. Forc=0.01 at %H _HF=?454.7(2.3)kG is deduced. The resonance shift with an external magnetic field has been studied precisely, yieldingK=0.012(23) andK=0.026(12) for the Knight-shift of¹⁹²Ir in Fe and Ni, respectively.     

NMR/ON of206BiFe produced by decay of cold implanted206Po

²⁰⁶Po was implanted into iron at T<0.2 K. After electron capture decay to²⁰⁶Bi nuclear magnetic resonance of oriented²⁰⁶BiFe was observed with an asymmetric resonance line shape. Evaluation of the data with the superposition of two Gaussian lines results in ν=693.7(2) MHz for the center frequency of the narrow one of the two lines at external field zero. From this B_hf (BiFe)=119.0(1.3) T is derived. The effective spin-lattice relaxation time of²⁰⁶BiFe at T=13 mK was measured as Ti=0.94(5) s.     

A fast, low perturbation ionization beam profile monitor based on a gas-jet curtain for the ultra low energy storage ring

An ionization beam profile monitor relying on a supersonic gas-jet shaped into an extended, thin curtain is proposed for operation in an ultra high vacuum environment for very low perturbation on the accelerated beam, as requested for the in-ring profile monitoring at the Ultra low energy Storage Ring (USR) at the Facility for Low-energy Antiproton and Ion Research (FLAIR), in Darmstadt. In this paper, we describe the working principle of the monitor, as well as providing an analysis of sensitivity and resolution dependence on geometrical design and gas curtain thickness.     

Low-temperature nuclear orientation of173Lu,175Hf,178Ta and182m,183,184,186Re in Re

Quadrupole-interaction nuclear-orientation experiments were performed on dilute samples of the Group IIIb and IVb impurities¹⁷³Lu and¹⁷⁵Hf in a (Group VIIb) Re single crystal, the samples being preparedin situ by irradiation of a Re single crystal with 172.5 MeV alpha particles. From the γ-anisotropies at temperatures down to 8mk the quadrupole interaction frequencies Ν_Q=e²qQ/h of¹⁷³LuRe and¹⁷⁵HfRe were determined to be ?1149 (100) and ?540 (43) MHz, respectively. The negative sign in both cases indicates that the direction of the electric field gradient (EFG) at the impurity sites is fixed uniquely by the properties of the host lattice. The absolute magnitudes of these EFG's differ strongly from that of the pure system ReRe; the electronic contribution to the EFG of different impurities in Re decreases with increasing impurity valence, contrary to the expectation. As a byproduct, the quadrupole splittings of¹⁷⁸Ta,^{182m, 183, 184, 186}Re in Re were measured to be ?103(10), ?502(30), ?281(20), ?340(22) and ?73(7) MHz.     

The MTV experiment: a test of time reversal symmetry using polarized 8Li

The MTV (Mott Polarimetry for T-Violation Experiment) experiment at TRIUMF-ISAC (Isotope Separator and ACcelerator), which aims to achieve the highest precision test of time reversal symmetry in polarized nuclear beta decay by measuring a triple correlation (R-correlation), is motivated by the search for a new physics beyond the Standard Model. In this experiment, the existence of non-zero transverse electron polarization is examined utilizing the analyzing power of Mott scattering from a thin metal foil. Backward scattering electron tracks are measured using a multi-wire drift chamber for the first time. The MTV experiment was commissioned at ISAC in 2009 using an 80 % polarized ⁸Li beam at 10⁷ pps, resulting in 0.1 % statistical precision on the R-parameter in the first physics run performed in 2010. Next generation cylindrical drift chamber (CDC) is now being installed for the future run.     

Characterization of two dissimilatory sulfite reductases from sulfate-reducing bacteria

Mössbauer, EPR, and biochemical techniques were used to characterize two dissimilatory sulfite reductases: desulforubidin fromDesulfovibrio baculatus strain DSM 1743 and desulfoviridin fromDesulfovibrio gigas. For each molecule of desulforubidin, there are two sirohemes and four [4Fe?4S] clusters. The [4Fe?4S] clusters are in the diamagnetic 2+ oxidation state. The sirohemes are high-spin ferric (S=5/2) and each siroheme is exchanged-coupled to a [4Fe?4S]²⁺ cluster. Such an exchange-coupled siroheme-[4Fe?4S] unit has also been found in the assimilatory sulfite reductase fromEscherichia coli/1/ and in a low-molecular weight sulfite reductase fromDesulfovibrio vulgaris/2/. For each molecule of defulfoviridin, there are two tetrahydroporphyrin groups and four [4Fe?4S]²⁺ clusters. To our surprise, we discovered that about 80% of the tetrahydroporphyrin groups, however, do not bind iron.     

Preliminary design studies of an extraction of the USR

The next-generation Facility for Low energy Antiproton and Ion Research (FLAIR) at GSI is going to be a dedicated research facility for ion research in the keV range. These ion beams will allow to explore fundamental properties in matter-antimatter research at ultra-low energies of only 20 keV/q in hitherto impossible experiments. To provide these very low energy beams, the Ultra-low energy Storage Ring (USR), an electrostatic synchrotron, will play a major role within the FLAIR complex. It combines the electrostatic storage mode with deceleration from an initial energy of 300 keV/q down to 20 keV/q—as well as an efficient beam cooling. To fulfill its role as a multi-purpose experimental facility, the design of the USR has not only to cover in-ring experiments, but needs to include a highly flexible beam extraction for serving different external experiments as well.     

Description of high-spin isomers in theN=82 region

The high spin states and of those especially the yrast isomers are studied in the region near the rare earth nuclei. The deformation energy surface is calculated with a method modelled in principle according to a shape constrained cranked HF theory (CHF). In practice, the expectation value of the many-body Hamiltonian is calculated with cranked Nilsson functions. One finds rotation around a slightly deformed oblate or prolate symmetry axis in front or behind the rare earth region, respectively. Near the Hf isotopes strongly prolate deformed nuclei rotating around the symmetry axis are found in agreement with the knownK isomers in this region. These results are explained also qualitatively with the help of the MONA (Maximisation of theOverlap ofNucleonic wave functions byAlignment of single particle angular momenta) effect. In the second part high spin states and yrast isomers in theN=82 region are calculated in the cranked Hartree-Fock-Bogoliubov approach with four and six quasi-particle excitations. For the excitation energies in¹⁴⁶Gd and¹⁵²Dy and a measuredg factor one finds satisfactory agreement.     

Description of high-spin isomers in theN=82 region

The high spin states and of those especially the yrast isomers are studied in the region near the rare earth nuclei. The deformation energy surface is calculated with a method modelled in principle according to a shape constrained cranked HF theory (CHF). In practice, the expectation value of the many-body Hamiltonian is calculated with cranked Nilsson functions. One finds rotation around a slightly deformed oblate or prolate symmetry axis in front or behind the rare earth region, respectively. Near the Hf isotopes strongly prolate deformed nuclei rotating around the symmetry axis are found in agreement with the knownK isomers in this region. These results are explained also qualitatively with the help of the MONA (Maximisation of theOverlap ofNucleonic wave functions byAlignment of single particle angular momenta) effect. In the second part high spin states and yrast isomers in theN=82 region are caluclated in the cranked Hartree-Fock-Bogoliubov approach with four and six quasi-particle excitations. For the excitation energies in¹⁴⁶Gd and¹⁵²Dy and a measuredg factor one finds satisfactory agreement.     

Perturbed αγ-angular correlations in the decay of228Th

At external magnetic fields between 1.3 and 22.5 kG the integral αγ-angular correlations of theO ⁺(α)2⁺(γ)O ⁺ cascades from the ground states of²²⁸Th and²²⁴Ra respectively implanted into iron and aluminum lattices have been studied. The data were analyzed assuming different additional time dependent and static perturbations. The rotation of the angular correlation for Ra in Al proved independent of these assumptions. Therefore ag-factor of the 84.4 keV 2⁺ state in²²⁴Rag=0.46 (11) could be derived. Although static electric interactions seem the most probable cause for the attenuations observed for Ra and Rn implanted into Fe it was found that the two parameter Abragam and Pound theory better reproduces the data than the one parameter static perturbations. Therefore the hyperfine fields experienced by Ra and Rn in Fe were derived using Abragam and Pound theory to beH _HF(RaFe)=?127(31) kG andH _HF(RnFe)=1095 kG.     

Frequency dependence of the freezing temperature in spin glasses: A comparative study of (La,Gd)B6, (Y,Gd)Al2 and (La,Gd)Al2

The frequency dependence of the freezing temperatureT _f(ν) is determined for the dilute spin glass systems (La, Gd)B₆ and (Y, Gd)Al₂ in the frequency range 10–1,000 Hz. While for (La, Gd)B₆,T _f(ν) is found to be weak, for (Y, Gd)Al₂ T _f(ν) is even stronger than for the previously studied system (La, Gd)Al₂. Both, measurements of the temperature dependence of the susceptibility nearT _f and calculations of the RKKY pair interaction, suggest that this difference is correlated with a different sign of the nearest-neighbor interaction, which appears to be antiferromagnetic for (La, Gd)B₆ and ferromagnetic for (Y, Gd)Al₂ as well as (La, Gd)Al₂.     

NMR-on of182Ta and183Ta in Fe

Nuclear magnetic resonance has been observed on radioactive¹⁸²Ta and¹⁸³Ta oriented at low temperature in an Fe host, by detection of the change in spatial anisotropy of γ-rays emitted during nuclear decay. By measuring the resonant frequencies of¹⁸³Ta in four different applied magnetic fields the nuclear magnetic moment and hyperfine field have been deduced. These are: $$|\mu \left( {{}^{183}Ta; I = \tfrac{\user2{7}}{\user2{2}}} \right)| = 2.28(3)\mu _{\rm N} and B_{hf} \left( {Ta\underline {Fe} at 0 K} \right) = - 67.2(1.3)T$$ . The spin of the ground state of¹⁸²Ta has been determined asI=3 by comparing resonance results with those obtained in a thermal equilibrium nuclear orientation study. The ratio of the resonant frequencies observed for¹⁸²Ta and¹⁸³Ta at one applied field value yields a magnetic moment for the former of $$|\mu \left( {{}^{182}Ta; I = \user2{3}} \right)| = 2.91(3)\mu _{\rm N} $$ . The spin lattice relaxation time for¹⁸³TaFe (0.12 at% Ta) at 18 mK in an applied field of 0.5 T has been found to be 40(10) s.     

A reexamination ofSU(6) symmetry breaking in high-energy phenomenology

A permutationally-symmetric form for the nucleon wave function consisting of a linear combination of the56 ground state and the70 excited state is used to reexamine the nucleon structure functions and form factors. This form of wave function reproduces the results of the successful Carlitz-Kaur model, differing only in the addition of a term that is proportional to the square of the mixing coefficient between the56 and the70 states. Values of this mixing coefficient are obtained from the structure functions and from the initial slope of the neutron electric form factor using relativistic wave functions constructed by Henriques, Kellett, and Moorhouse. The signs of these values are in agreement, so that the model avoids the contradiction noted by Le Yaouanc et al. This result is due to the dependence of the neutron electric form factor calculation on the spin wave function and associated matrix elements.     

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.