Carlos Costa Dantas

A particle system approach to industrial tomographic reconstruction

This work introduces a novel tomographic reconstruction, using a very small number of projections, suitable for industrial applications. The particle system iterative reconstruction technique represents reconstructing material as a set of particles with certain physical features, subject to a group of forces, which can produce movement. The system constantly updates the net of particles by repositioning them in such a way as to approach the equilibrium. The elastic potential along a trajectory is a function of the difference between the attenuation coefficient in the current configuration and the corresponding input data. In this work, we present a simple analysis of the resulting reconstruction in a simulation with sinograms produced from some phantoms, including a comparison with some established iterative methods.

Radio-isotope neutron activation analysis for vanadium, manganese and tungsten in alloy steels

Abstract An instrumental neutron activation method for V, Mn and W in alloy steels with a 241 Am/Be isotopic neutron source is described. The samples were irradiated to induce the nuclear reactions 51 V(n, γ) 52 V, 55 Mn(n, γ) 56 Mn, and 186 W(n, γ) 187 W. The activities were measured with a NaI(TI) detector. Interferences on the measured photopeaks were shown to be negligible by measuring the half-lives of 62 V, 56 Mn and 187 W.These thre elementes were determined in the range 1.5–12.9% in special steels; manganese in the range 0.5–1.6% was measured in cast irons. Calibration was done by comparison with results from wet chemistry and x-ray fluorescence spectrometry. The processing times for the vanadium, manganese and tungsten determinations were 11 min, 3 h and 26.3 h, respectively, but these were reduced greatly by intoruding a scheme wherein six samples were simultaneously irradiated and the 56 Mn and 187 W nuclides were measured sequentially for a series of 66 samples. The average processing time was reduced to 45 min for tungsten with a precision of 4.0% and accuracy of 3.4% and 22.8 min for manganese with a precision of 3.8% and accuracy of 3.1%.