Measurement of thermal neutron cross section and resonance integral for the (165)Ho(n, gamma)(166g)Ho reaction

The ground state thermal neutron cross section and the resonance integral for the (165)Ho(n, gamma)(166)Ho reaction in thermal and 1/E regions, respectively, of a thermal reactor neutron spectrum have been measured experimentally by activation technique. The reaction product, (166)Ho in the ground state, is gaining considerable importance as a therapeutic radionuclide and precisely measured data of the reaction are of significance from the fundamental point of view as well as for application. In this work, the spectrographically pure holmium oxide (Ho(2)O(3)) powder samples were irradiated with and without cadmium covers at the IEA-RI reactor (IPEN, Sao Paulo), Brazil. The deviation of the neutron spectrum shape from 1/E law was measured by co-irradiating Co, Zn, Zr and Au activation detectors with thermal and epithermal neutrons followed by regression and iterative procedures. The magnitudes of the discrepancies that can occur in measurements made with the ideal 1/E law considerations in the epithermal range were studied. The measured thermal neutron cross section at the Maxwellian averaged thermal energy of 0.0253 eV is 59.0 +/- 2.1 b and for the resonance integral 657 +/- 36b. The results are measured with good precision and indicated a consistency trend to resolve the discrepant status of the literature data. The results are compared with the values in main libraries such as ENDF/B-VII, JEF-2.2 and JENDL-3.2, and with other measurements in the literature.

Magnetic structures of quaternary intermetallic borocarbides RCo(2)B(2)C (R = Dy, Ho, Er)

The magnetic structures of the title compounds have been studied by neutron diffraction. In contrast to the isomorphous RNi(2)B(2)C compounds, wherein a variety of exotic incommensurate modulated structures has been observed, the magnetic structure of ErCo(2)B(2)C is found to be a collinear antiferromagnet with k = (12, 0, 12) while those of HoCo(2)B(2)C and DyCo(2)B(2)C are observed to be simple ferromagnets. For all studied compounds, the moments are found to be confined within the basal plane and their magnitudes are comparable to the values obtained from the low-temperature isothermal magnetization measurements. The absence of modulated magnetic structures in the RCo(2)B(2)C series (for ErCo(2)B(2)C, verified down to 50 mK) is attributed to the quenching of the Fermi surface nesting features.

Spin contamination in XOO radicals X = F, Cl, Br, HO: How is the investigation of the HOOO radical affected

We have analysed the effect of spin contamination in the wavefunction of HOOO. At least, two solutions can be found for the HF wavefunction. One, lower in energy, presents a high spin contamination and gives qualitatively incorrect structural parameters. On the other hand, the less contaminated HF reference gives structural parameters that are in better agreement with experiment, and positive spin densities on all atoms. Some of the problems described during previous investigations of HOOO can now be traced to problems in the HF reference. For the first time we report a CCSD(T) estimation of the structure of HOOO cis employing a HF reference with small spin contamination. (C) 2008 Elsevier B.V. All rights reserved.