Showing papers by "National Nuclear Energy Commission published in 1988"

Multielemental analysis of Brazilian milk powder and bread samples by neutron activation

Abstract: The concentrations of Na, Cl, Mn, Br, Fe, Zn, Rb, Sb, Sc, Cr, Al and Mg were determined in some types of bread and in some brands of milk powder consumed in the city of Sao Paulo (SP—Brasil), by instrumental neutron activation analysis. Radiochemical separations were carried out by means of retention of24Na on hydrated antimony pentoxide (HAP) from a 8N HCl solution, after digestion of the organic matter. It was possible in this way to determine the radioisotopes64Cu,69mZn and140La in the effluent solution. The detection limits of the trace elements analyzed in bread and milk powder samples were determined using the Currie and Girardi criterions.

Multiphoton gas phase dissociation of methyl and ethyl formates

Abstract: The IR-multiphoton-initiated decomposition of methyl and ethyl formates is reported. Experiments were carried out by 9.6 μm irradiation under mildly focused conditions, with fluences of about 10 J cm −2 . CO, CH 4 , CO 2 , C 2 H 6 and CH 3 OH were detected for HCOOCH 3 while CO, CH 4 , C 2 H 4 , C 2 H 2 and traces of CO 2 were observed for HCOOC 2 H 5 . The product yields were measured by quantitative gas chromatographic analyses. In HCOOC 2 H 5 , the dominant process is the reaction producing ethylene and CO (already observed in pyrolysis and UV photolysis). In HCOOCH 3 two presumably unimolecular reactions seem to occur, one producing CO and CH 3 OH and the other producing CH 4 and CO 2 , in contrast with the assumed mechanisms for pyrolysis and photolysis. The product yields can be interpreted in terms of secondary thermal or radical reactions. The effects of inert gases were studied. Luminescence in the focal region originating from OH·, CH·, C 2 and H 2 O(113) excited species was observed and its temporal behavior studied.

Neutron emission spectra obtained by a double neutron-gamma discrimination technique

Abstract: A technique to obtain neutron emission energy spectra above 2 MeV from (x,n) nuclear reactions using NE-213 liquid scintillator and a pulsed accelerator was investigated. After selection of the neutron light pulses both by pulse shape discrimination and time correlation with the cyclotron microstructure pulses, the light output spectrum is unfolded to yield the energy spectrum. Neutron background, flight paths, beam current pulse time resolution and time uncorrelated gamma-ray light pulses are discussed. It is concluded that it is feasible with this technique to obtain double differential neutron emission spectra to measure nuclear level densities.

Production of no carrier added residue free 22Na

Abstract: A method for the production of no carrier added and residue free22Na, was developed via the24Mg/d, α/22Na nuclear reaction applying 14 MeV deuterons and a high current Mg−Cu target. The yield for the reaction target. The yield for the reaction was measured and the chemical separation performed using a Dowex 50WX8 resin in H+ form. The overall yield was higher than 98%. Residue could not be detected. All experiments were carried out at IEN's CV-28 cyclotron.

Laboratory Experiments on 60Co Bioaccumulation by Tropical Seaweeds

Abstract: The first Brazilian nuclear power plant, presently operating commercially, was constructed in Angra dos Reis county, a coastal site at about mid distance between Rio de Janeiro and Sao Paulo. Unit 1 of Angra Nuclear Power Plant Site (ANPPS) is a 683 MW (e) Westinghouse PWR reactor and units 2 and 3, presently under construction, are KWU designed PWR reactors of 1200 MW (e) output each. As a consequence of the development of the ANPPS many environmental studies have been iniciated by the operator (FURNAS), the supervising authority (CNEN) and independent research groups. Those related to the aquatic environment, were studies of the structure and distribution of seaweed and fish communities, fish food habits, field and laboratory experiments on the retention of radionuclides and stable elements by marine biota and sediments, as well as geochemical and hydrodynamic studies.

Isotope dilution alpha spectrometry with spike enriched in233U for the determination of uranium in geological samples

Abstract: Isotope dilution alpha spectrometric /IDAS/ method has been developed for the determination of uranium in geological materials. The spike employed as uranium enriched in the isotope 233. The results of the analysis for rock and ore samples show that the precision and accuracy of the method are comparable to other analytical techniques and the method can be employed for routine analysis.

Kinetic decay of H· in the radiolysis of tetracycline hydrochloride in powder form at 77 K+

Abstract: Kinetic decay of paramagnetic species formed in the radiolysis of tetracycline hydrochloride in powder form, at 77 K, shows that most of the H· is not able to migrate. Geminate recombination between H· and its partner is the main reaction: H·+TC· → TCH, although a few H· succeed in diffusing slowly. But when H· acquires enough kinetic energy to migrate, it reacts preferentially with species different from its partner. The e− is not observed by ESR, at 77 K, although tetracycline hydrochloride is a chemical trap for e− in methanol, benzyl alcohol and alkaline aqueous solutions. In the radiolysis of tetracycline hydrochloride in powder form, the dimethylammonium group blocks H· abstraction reaction at 77 K.

Calculation of Response Matrices for PWR Heterogeneous Assemblies by Perturbation Method

Abstract: Accurate solution of the group diffusion equations for PWR cores requires explicit treatment of the non-homogeneous macroscopic parameters within each fuel assembly. It is argued that the response matrix approach is a convenient method to handle this problem provided all matrix elements for the non-homogeneous assemblies can be computed. This so called local problem is solved in this paper by a perturbation algorithm which leads to sensitivity coefficients for the power series expansions of the response matrix elements. A numerical study for 2 representative assemblies of the Indian Point Unit No. 2 (IP2) reactor is carried out and response matrices obtained by the perturbative method are compared with values computed by a finite difference program.