National Nuclear Energy Commission

About: National Nuclear Energy Commission is a government organization based out in Rio de Janeiro, Brazil. It is known for research contribution in the topics: Dosimetry & Laser. The organization has 3816 authors who have published 4694 publications receiving 59951 citations.

Optimised k0-instrumental neutron activation method using the TRIGA MARK I IPR-R1 reactor at CDTN/CNEN, Belo Horizonte, Brazil

Abstract: The Nuclear Technology Development Centre/Brazilian Commission for Nuclear Energy, CDTN/CNEN, is the only Brazilian Institution to apply the k 0 -standardisation method of instrumental neutron activation technique determining elements using its own nuclear reactor, TRIGA MARK I IPR-R1. After changes in the reactor core configuration, the reactor neutron flux distribution in typical irradiation channels had to be updated, as well as the parameters f and α , needed to apply the k 0 -method of neutron activation analysis. The neutron flux distribution in the rotary rack was evaluated through the specific count rate of 198 Au and the parameters f and α , were determined in five selected channels applying the “Cd-ratio for multi-monitor” method, using a set of Al-(0.1%)Au and Zr (99.8%) monitors. Several reference materials were analysed, indicating the effectiveness of the improved method.

Alkali-metal-doping dynamics and anomalous lattice contraction of individual debundled carbon nanotubes

Abstract: The dynamics of K doping of thin films of semiconducting debundled single-walled carbon nanotubes (SWNTs) on a $\mathrm{Si}∕{\mathrm{SiO}}_{2}$ substrate is followed using in situ Raman scattering. Similar to the behavior we observed in the Cs doping of bundled SWNTs, four distinct intervals during doping can be distinguished via the behavior of the high frequency tangential band (or G-band) scattering. We therefore find that the character of the time evolution of the frequency and linewidth of the most prominent G band with alkali-metal doping is almost identical for debundled and bundled tubes. This includes the observation of an anomalous upturn in the G-band frequency during the third interval of doping that is consistent with a contraction of the $\mathrm{C}\mathrm{C}$ bond within the tube wall. We conclude that this anomalous contraction is not associated with doping-induced changes in the tube-tube interaction within a bundle, but is an intrinsic, and yet unexplained, consequence of an upshifting Fermi level in debundled $n$-doped SWNTs. A long induction period between when doping conditions are established and when changes in the Raman spectrum occur is observed and remains unexplained.

Synthesis of nanocrystalline yttrium disilicate powder by a sol–gel method

Abstract: In the present work a new route for the synthesis of α-Y2Si2O7 is reported. The method consists in the gelation of an acid solution composed by Y(NO3)3 and tetraethylorthosilicate (TEOS) in the adequate molar ratio to form a precusor complex gel containing the Y3+ and Si4+ cations in the 1:1 ratio, which yields the stoichiometric α-Y2Si2O7 after calcining. The nanosize powder of Y2Si2O7 obtained at 1060°C was characterised by XRD and TEM. The conditions and main parameters such as temperature, pH or time for the hydrolysis of the Y(NO3)3/TEOS solution in HCl medium was investigated and optimised to obtain the precursor gel which was analysed by DTA and TGA.