New determination of the nuclear-quadrupole moment of the NMR probe 99Tc ground-state

ERRICO L.A.,; DARRIBA G.N.; RENTERÍA M.

La Plata

Workshop; HFILP2005, International Workshop “35th Anniversary of Hyperfine Interactions at La Plata"; 2005

Laboratorio de Espectroscopía Nuclear e Interacciones Hiperfinas, FCE, UNLP e IFLP (CONICET)

The experimental study of hyperfine interactions is often used as a powerful toolto characterize different atomic sites in a given material and to obtain inf ormation aboutelectronic, magnetic and structural properties of solids [1]. In the case of pure electric-quadrupole interactions, the measured quantities are the quadrupole coupling constantnuQ = eQV33/h and the asymmetry parameter eta = (V11-V22)/V33, where Vii (i = 1, 2, 3) arethe components of the diagonalized electric -field gradient (EFG) tensor with theconvention | V33|>|V22|>|V11|. The EFG is measured via its interaction with the nuclear-quadrupole moment Q of a suitable probe-atom (generally an impurity in the systemunder study) by different techniques, such as Mössbauer Spectroscopy, NuclearMagnetic and Nuclear-Quadrupole Resonance (NMR and NQR) or Perturbed-AngularCorrelations (PAC). Since the EFG tensor is directly related to the asphericity of theelectronic density in the vicinity of the probe nucleus, the determination of thequadrupole coupling constant nQ allows the investigation of electronic and structuralproperties in the solid, provided Q is known. Although Q is a purely nuclear quantitity,the quadrupole moments for some isotopes are only known with limited accuracy andtheir determination is still an active field of research.One of the possible methods to determine Q is to use information ofexperimental quadrupole coupling constants and accurate theoretical EFG calculations.In this work we present a new determination of the nuclear-quadrupole moment of theground state (I = 9/2 + ) of 99 Tc. This nuclear state is used as nuclear probe in NMRspectroscopy. This determination was obtaine d by comparing experimentallydetermined nuclear-quadrupole frequencies with the EFG calculated at Tc sites inmetallic Tc using the ab initio “Full-Potential Linearized-Augmented Plane Waves”method [2] in the framework of the Density Functional Theory. The obtained result forthe quadrupole moment, |Q(99 Tc, 9/2 + )| = 0.141 b, has an indetermination ten timessmaller than those previously reported in the literature [Q(99 Tc, 9/2 + ) = +0,3434 b [3];Q(99 Tc, 9/2 + ) = +0,2810 b [4]]. These determinations are compared with predictions ofthe nuclear shell model. The sign of the 99 Tc quadrupole moment is also discussed.[1] See, e.g,, Proc. of the 13th International Conference on Hyperfine Interactions,Bonn, Germany, 2004, Hyp. Interact., 2004, in press.[2] S.H. Wei and H. Krakauer, Phys.Rev.Lett. 55, 1200 (1985).[3] K. Kessler and R. Trees, Phys.Rev. 92, 303 (1953).[4] R. Kidd, J. Mag. Resonance 45, 88 (1981).Keywords: 99 Tc, nuclear-quadrupole moment, FP-LAPW, ab initio, EFG, NMR