On the Richardson-Lucy Algorithm with A Varying Point Spread Function along The Iterations

Abstract: This work analyses the soundness of two algorithms, Fishsint and Almexp to improve images using the Richardson-Lucy (RL) algorithm under a varying Point Spread Function (PSF) along the iterations. A plethora of methods based on Richardson-Lucy has been published, but no further proposal involving such an alternative has been published. Whereas the unnamed predecessor of Fishsint addressed only small size synthetic images under a blind fashion procedure, Fishsint and Almexp employs an algorithm Wdet to determine the initial PSF and all subsequent values after each iteration, respectively. Fishsint performs a loop, where the last determined PSF improves the previously obtained image and vice versa. Its original unnamed version has been modified in the present work by entering a previously determined initial PSF to accelerate the convergence. The algorithm Almexp, as well, uses the algorithm Wdet to determine the PSF of the last obtained image to deconvolve itself. Therefore, whereas the Fishsint unnamed predecessor used an initial guess PSF - chosen by the customer - Almexp determines the PSF always through the algorithm Wdet. Fishsint and Almexp furnish final images which outperform those obtained with the original Richardson-Lucy approach working under a constant PSF along the iterations. Hence, in order to carry out a comparison between their performances, all the algorithms have been embedded into an ad hoc written Fortran 90 program. The results corroborate the soundness of a varying PSF along the iterations with the Richardson Lucy algorithm. Keywords: Richardson-Lucy, varying PSF along iterations, image improvement, neutron radiograph

Programa computacional para cálculo do tempo de ativação fluxo de nêutron e atividade de amostras

O PARAMETRO é um programa desenvolvido em Turbo-Pascal usado em várias aplicações nucleares onde são envolvidas irradiações de amostras, como análise por ativação com nêutrons. É constituído de 3 programas independentes para determinação do tempo de irradiação, da atividade de amostras ou do fluxo de nêutrons. Consta também de um arquivo de dados denominado LIB contendo informações de 88 isótopos diferentes, alguns dos quais os raios gama de múltiplas energias

Comportamento do fluxo de nêutrons térmicos e epitérmicos na saída do canal J-9 do Reator Argonauta para a obtenção de imagens radiográficas

Neste trabalho foi verificado o comportamento do fluxo de nêutrons térmicos e epitérmicos em toda área de saída do canal J-9 do reator Argonauta para diversos arranjos de colimação. O objetivo principal foi definir um arranjo otimizado para ser utilizado na obtenção de imagens radiográficas com nêutrons, incluindo tomografias e neutrongrafias. Como a homogeneidade do feixe e a energia dos nêutrons são fatores que influenciam na qualidade das imagens de um objeto radiografado, a área do canal foi dividida em treze seções e, em cada uma foi obtido o fluxo absoluto de nêutrons térmicos e epitérmicos para cada arranjo de colimação. Os valores dos fluxos em cada seção foram determinados pela ativação (n,γ) de folhas de índio colocadas em cada posição. O método de diferença de cádmio foi o utilizado para separar a contribuição dos nêutrons térmicos dos epitérmicos

Programa computacional para cálculo de fluxo de neutrons

O valor absoluto do fluxo de nêutrons é um parâmetro importante em Física de Reatores e outras aplicações no campo nuclear. Devido a várias correções necessárias como decaimento radioativo dos nuclídeos produzidos, fatores de normalização entre diferentes irradiações, perturbação do espectro de nêutrons, comportamento da seção de choque, subida de potência do reator e outros, faz com que o cálculo do fluxo de nêutrons seja bastante trabalhoso. O software FLUXO foi desenvolvido para vencer essas dificuldades. É programado em linguagem FORTRAN e tem como objetivo principal o cálculo do fluxo absoluto de nêutrons térmicos, epitérmicos e rápidos através da técnica de ativação de folhas. Essa ativação pode ser medida pela técnica de coincidência 4pb-g ou somente por espectrometria g. O software também calcula, através dessas duas técnicas, a atividade absoluta de fontes radioativas e de amostras irradiadas no reator

Comparison of tomagraphic systems for X-rays and thermal neutrons

In this work tomographic images of the very same object have been taken with 25 keV X-rays neutrons (E=0.025 eV) aiming to demonstrate that a thermal neutron tomography in some cases is a complementary technique to the X-ray tomography, such as in the examination of hydrogen-bearing compounds contained in a metalic matrix for instance. The capability of the neutron to pass through metallic materials si=uch as lead, stainess steel and aluminium, allows the detection of encapsulated plastic explosives and visualize their inner structure like density variations, voids and alien materials, which are important features for the quality control of the final product. To obtain the images, a 3rd generation tomographic system equipped with an 8-cm long carbon window, and the detecotr filled with AR CH4 under 2 atm-pressure. The X-ray beam was supplied by an ampoule with a tungsten anode manufactured by gas replaced by 3He-enriched helium, acting simultaneously as neutron source fumished the 4,5 x 105 n.cm-2 s-1 thermal neutron beam at is main channel exit, where the tomographic system was installed

A position sensitive gas detector for tomography with thermal neutrons

A position sensitive gas detector originally designed for X-ray detection has been modified for the detection of termal neutrons aiming its utilization in tomography. This work describes the modifications done for this purpose, including the incorporation of neutron to-charged particle converter materials, as well as the measurements carried out to evaluate the detector performance for each of them. The first converter studied was a natural gadolinium foil placed close to the detector window, which produces an internal conversion electron arising from the interaction of the neutron with the gadolinium nucleus. This electron causes the aimed ionization in the standard argon-methane filling gas, as used in conventional X-ray detectors. Another converter studied was high-enriched 3 He, replacing thus both former gadolinium foil and the argon-methane. The 3 He fulfills the main requirements for thermal neutron detection due to its excellent features such as high absorption cross section reaching 5330 barns, low efficiency for gamma-ray conversion and good charge amplification factor. The 3He -3 (n,p)3H nuclear reaction releases 764keV, impinging 573keV to the proton and 191 keV to the tritium particles which are emitted practically into opposite directions, since the neutron otself, due to its very low energy (0.025eV) doesn’t contribute significantly to the momentum balance. Termographic systems with thermal neutrons incorporating the developed detector, present some advantages with regard to the earlier 1st generation equipment, sch as a better resolution and a reduction in the image acquiring time.The prototype of the detector used in this work has been manufactured at the Laboratorio de Detetores/CBPF, while all the experimental work has been carried out at the Instituto de Engenharia Nuclear – IEN/CNEN using its Argonauta reactor and facilities, as well as pieces of equipment provide by Laboratorio de Isntrumentação Nuclear-COPPE/UFRJ