Rb Nuclei Research Articles

NMR determination of the nonclassical critical exponents beta and beta -bar in incommensurate Rb2ZnCl4.

The critical behavior below the second-order transition between the normal and the incommensurate phase of ${\mathrm{Rb}}_{2}$${\mathrm{ZnCl}}_{4}$ is studied by means of quadrupolar perturbed NMR. The temperature dependences of the $^{87}\mathrm{Rb}$ m=\ifmmode\pm\else\textpm\fi{}1/2\ensuremath{\leftrightarrows}\ifmmode\pm\else\textpm\fi{}(3/2 satellite transitions are investigated for different Rb nuclei and different crystal orientations. It is shown that the critical exponents \ensuremath{\beta} and \ensuremath{\beta}\ifmmode\bar\else\textasciimacron\fi{}=2-\ensuremath{\alpha}-\ensuremath{\varphi}\ensuremath{\ne}2\ensuremath{\beta}, \ensuremath{\varphi} being the crossover exponent associated with an uniaxial perturbation, can be determined accurately. The value \ensuremath{\beta}=0.35\ifmmode\pm\else\textpm\fi{}0.01 and \ensuremath{\beta}\ifmmode\bar\else\textasciimacron\fi{}=0.83\ifmmode\pm\else\textpm\fi{}0.03 obtained are in agreement with the theoretical predictions of the three-dimensional XY model.

Search for superdense nuclei of Rb and Cs among the products of 8 GeV proton interactions with Ta

Experimental searches for β-active superdense nuclei of Rb and Cs among the products of 8 GeV proton interactions with Ta are described. The method of selective off-line mass-separation with scanning of the β-activity distribution on the collector was used. According to π-condensation theory, the long-lived anomalous nuclei are expected to be more neutron-deficient than the usual ones. Moreover, their mass numbers may be significantly nonintegral measured on the normal mass scale, because of unusual binding energy. These predictions guided the present search. No anomalous nuclei were found. The upper limit for Rb nuclei in the range 69 ⩽ A ⩽ 78 is 10 −5 with respect to the yield for 81Rb; for Cs in the range 112 ⩽ A ⩽ 122 the limit is (5–10) × 10 −6 of the yield for 127Cs. These estimations are based on the assumption that the half-life of superdense nuclei equals 5 h.

Hyperfine structure and isotope shift of theD2line ofRb76−98and some of their isomers

Hyperfine structure, spin, and isotope shift measurements have been performed on $^{76\ensuremath{-}98}\mathrm{Rb}$ and $^{78,81,82,84,86,90}\mathrm{Rb}^{m}$. The Rb nuclei have been produced either by spallation of Nb or by fission of U by a 600 MeV proton beam. They have been separated in mass before being transformed into a thermal atomic beam which interacts at a right angle with the light from a c.w. tunable dye laser. The charge radii changes deduced from the isotope shifts exhibit shell effects at $N=50$ and deformations at $N=60$, which are discussed.NUCLEAR STRUCTURE $^{76\ensuremath{-}98}\mathrm{Rb}$, $^{78,81,82,84,86,90}\mathrm{Rb}^{m}$. Measured hyperfine constants $A(5s^{2}\mathrm{S}_{\frac{1}{2}})$, $A(5p^{2}\mathrm{P}_{\frac{3}{2}})$, $B(5p^{2}\mathrm{P}_{\frac{3}{2}})$; spins, isotope shifts. Deduced $\ensuremath{\mu}$, $\mathrm{Qs}$, $\ensuremath{\delta} 〈{r}^{2}〉$. High resolution laser spectroscopy on thermal atomic beams.

Atomic Reference Scale for Chemical Shifts of Rubidium

Abstract With a multi-nuclei Fourier transform NMR spectrometer the ratio of the Larmor frequencies of 85Rb and 2H in a solution of RbCl in D2O has been measured with high accuracy. The concentration dependence of the 85Rb NMR signals has been determined in solutions of rubidium salts in H2O and D2O. Using this dependence, the ratio of the Larmor frequencies of the 85 Rb nuclei for infinite dilution relative to 2 H in pure D20 is given. From this a gI-factor for 85Rb has been derived and has been compared with the gI-factor of an optical pumping experiment. The difference in the gI-factors results from the shielding of the rubidium nuclei by the water molecules around the ions. The shielding constant is σ(85Rb+) = -2.11 (2) · 10-4 . This yields a general atomic reference scale for the chemical shift of rubidium in the liquid and solid states and the possibility of comparing experimental and theoretical shielding constants.

Rb87Quadrupole Coupling and the Ferroelectric Transition in RbH2AsO4

The quadrupole-induced shifts of the ${\mathrm{Rb}}^{87}$ \textonehalf{} \ensuremath{\rightarrow} -\textonehalf{} NMR transition have been studied as a function of temperature and crystal orientation, and the electric-field-gradient (EFG) tensors at the Rb sites in Rb${\mathrm{H}}_{2}$As${\mathrm{O}}_{4}$ have been determined. In the ferroelectric phase there are two physically nonequivalent ${\mathrm{Rb}}^{87}$ EFG tensors ($A$ and $B$) which are related by the symmetry operations of the orthorhombic space group. In addition, each line is split into two components ($A$, ${A}^{\ensuremath{'}}$ and $B$, ${B}^{\ensuremath{'}}$) because of domain effects. The ${\mathrm{Rb}}^{87}$ quadrupole coupling constant equals 5.76 MHz at 108\ifmmode^\circ\else\textdegree\fi{}K, and the asymmetry parameter is $\ensuremath{\eta}==0.85$. The paraelectric EFG tensor is nearly, though not exactly, equal to the average of the two ferreolectric ones ($A$ and ${B}^{\ensuremath{'}}$, or ${A}^{\ensuremath{'}}$ and $B$) from oppositely polarized domains. The anomalous decrease in the quadrupole coupling constant of ${\mathrm{Rb}}^{87}$ with decreasing temperature in the paraelectric phase throws some light on the atomic motion as well as proton-lattice coupling and suggests that the Rb nuclei take part in collective atomic fluctuations which might represent an overdamped quasispin-wave ferroelectric mode.

Nuclear magnetic resonance in RbFeF3

The local magnetic fields on 19F, 87Rb and 85Rb nuclei have been measured in RbFeF 3. The parameters of hyperfine interaction and spin-densities on these nuclei have been calculated. There is a satisfactory agreement between experimental data and the theory suggesting that spin density on Rb nuclei is due to t 2g uncompensated spins.