In situ migration of tritiated water and iodine in Grimsel granodiorite,part II: assessment of the diffusion coefficients by TDD modelling

Diffusive transport of iodine (I) and tritiated water (HTO) in granodiorite is studied in the framework of the long term diffusion project (LTD) at the Grimsel Test Site, Switzerland. In this paper we modelled the tracer profiles measured in a long term (780 days) in situ diffusion test was carried out as part of LTD. The main outcome of the modelling tends to prove that the in situ apparent diffusion coefficients of I and HTO are close to the reference apparent diffusion coefficient determined in the laboratory (D _a = 3 × 10⁻¹⁰ m² s⁻¹).

     

Gravitational redshift experiments with the high-resolution Mössbauer resonance in67Zn

A gravitational tedshift (GRS) experiment using the high-resolution Mössbauer resonance in⁶⁷Zn is described. The tiny Doppler motion of the source can be checked by a dc-SQUID based displacement sensor. The results on the GRS strongly indicate that solid-state effects, which are difficult to control experimentally, finally limit the accuracy that Mössbauer measurements can provide in determining the GRS. We argue that for this reason conventional Mössbauer experiments most probably will not be able to compete with other methods in future GRS measurements of very high precision.     

Hydrolytic reactions of diadenosine 5',5'-triphosphate

The hydrolysis of diadenosine 5',5'-triphosphate to AMP and ADP has been studied over a wide pH-range. Under acidic conditions the reaction shows a first-order dependence on the hydronium ion concentration. Below pH 3 the rate-increase begins to level off. From pH 6 to 9 the hydrolysis is slow and pH-independent. Base-catalysed hydrolysis is observed in NaOH-solutions. Under alkaline conditions an intramolecular nucleophilic attack on the phosphate producing 3',5'-cAMP is also observed, but it is slower than the intermolecular reaction. Depurination of the adenosine moieties competes with the hydrolysis both under acidic and alkaline conditions, but the mechanisms are different. The temperature-dependence of the hydrolysis of Ap(3)A and the depurination of adenosine moieties were studied under acidic conditions, and the activation parameters of the reactions were calculated. The results of the work reflect the fact that the negatively charged polyphosphate group is very resistant towards nucleophilic attack. An efficient catalysis is only observed under acidic conditions, where the phosphate group becomes protonated. General acids or bases did not catalyse the hydrolysis. Furthermore, hydroxide ion catalysed cleavage is only observed at high base concentrations and other negatively charged nucleophiles did not attack the phosphate groups of diadenosine polyphosphates.     

Microscopic structure of fundamental excitations in N = Z nuclei

An extended mean-field model is presented that describes states of different isospin in odd-odd and even-even nuclei. Excitation energies of the T = 1 states in even-even as well as T = 0 and T = 1 states in odd-odd N = Z nuclei are calculated. It is shown that the structure of these states can be determined in a consistent manner when both isoscalar and isovector pairing collectivity as well as isospin projection (treated here within the isocranking approximation) are taken into account. In particular, in odd-odd N = Z nuclei, the interplay between quasiparticle excitations (relevant for the case of T = 0 states) and isorotations (relevant for the case of T = 1 states) explains the near degeneracy of these states.     

Rotations in isospace: a doorway to the understanding of neutron-proton superfluidity in N = Z nuclei

The T = 2 excitations in even-even N = Z nuclei are calculated within the isospin cranked mean-field approach. The response of pairing correlations to rotation in isospace is investigated. Whereas the isovector pairing rather modestly modifies the single-particle moment of inertia in isospace, the isoscalar pairing strongly reduces its value. This reduction of the isomoments of inertia with respect to its rigid body value is a strong indicator of collective isoscalar pairing correlations. These results are further generalized yielding beautiful analogies between the role of isovector pairing for the case of spatial rotations and the role of isoscalar pairing for the case of isorotations.     

Local structure and magnetism of Fe, Co and Ni doped Cr3Si

The lattice site occupation of 3d-type impurities in Cr₃Si doped with Fe, Co and Ni were studied using the Extended X-ray Absorption Fine Structure (EXAFS) technique, X-rays and magnetic susceptibility measurements. The EXAFS measurements were performed particularly carefully on the K-edge of chromium and cobalt. EXAFS data strengthened by simulations of the spectra show unambiguously that the impurities are occupying mostly Cr-sites. The magnetic state of the alloys has been studied theoretically using the Wien2k code. It is observed that if calculations are not carried out on an appropriately fine mesh of points in k-space, one can get the result indicating ferromagnetism although the overall magnetic moment per formula unit is weak.     

Correlated gamma rays in synchrotron radiation

A new intensity correlation phenomenon at gamma-ray wavelengths is described. The influence of detector size on correlation effects is analyzed quantitatively. It is shown that dedicated synchrotron radiation sources, such as the Mössbauer beam line at the ESRF, will have characteristics allowing experimental observations of the correlation phenomenon.     

Angular Distribution of Hyperfine Magnetic Field in Fe3O4 and Fe66Ni34 from Mössbauer Polarimetry

Nuclear resonance studies of the two different types impurity doped potassium hexachloro-stannates, the isomorphic system such as (K–Rb)₂SnCl₆ and K₂(Sn–Re)Cl₆ and the nonisomorphic system K₂SnCl₆:Al³⁺ in the high temperature cubic phase revealed contrasting features with one the other characterized by static in the former and dynamic feature in the latter case respectively. The resonance spectra of the nonisomorphic system indicate additionally a sign of the local structural transition above the conventional structural phase transition temperature. This seems to be triggered by the ligand-deficient octahedral defects and can be explained in terms of the enhanced activity of the octahedral defects for the hindered rotation.     

Studies of hyperfine interactions inRBa2(Cu1-x 57Fex)3O7-δ high-T c superconductors

Both⁵⁷Fe and¹⁵¹Eu Mössbauer resonances were used to study polycrystallineRBa₂Cu₃O_7-δ samples. The dependence of hyperfine interaction parameters on the oxygen deficiency δ is studied in detail with¹⁵¹Eu. For⁵⁷Fe spectra, a site assignment is proposed.