Operacionalização dos sistemas de movimentação cristal/detector e eletrônica de contagens do espectrômetro por dispersão em comprimento de onda para detecção de raios X característicos induzidos por feixe de elétrons

O principal objetivo do presente trabalho foi recuperar espectrômetro por dispersão em comprimento de onda (WDS, do inglês wavelength-Dispersive Spectrometer), desenvolver programas para controlar o movimento do conjunto cristal/detector e a eletrônica de contagem de fótons. A entrada de sinais analógicos relacionados à contagem de fótons e a saída de sinais digitais usados para controlar a varredura de janela para aquisição de altura de pulsos (PHA, do inglês Pulse-Height Analyzer) e do motor de passo, responsável pelo movimento cristal/detector, utilizou o dispositivo multifuncional modelo USB-6008 de aquisição de dados comandado pela linguagem de programação gráfica LabVIEW, ambos da National Instruments. Um dos programas realiza uma análise de PHA e o outro é responsável pela contagem de fótons de raios X com base no movimento serial do conjunto cristal/detector. Atividades adicionais incluíram a montagem da eletrônica de contagem e a recuperação e modificação do detector proporcional original. Os testes de bancada foram realizados com uma fonte radioativa de 57Co para produção de fótons. O espectro de PHA adquirido com um detector selado apresentou picos bem definidos em 6,4 keV (Fe Kα) e 14,4 keV (emissão gama), conforme observado na literatura. A aquisição do espectro PHA usando um detector proporcional de fluxo definiu as voltagens da linha de base e da janela para seleção dos pulsos relacionados ao Fe Kα. Usando esses parâmetros, a varredura do par cristal/detector mostrou o pico de Fe Kα na posição esperada.The main objective of the present work was to recover a wavelength-dispersive spectrometer (WDS) and develop softwares to control the crystal/detector movement and the photon counting electronics. The input of analog signals related to photon counting and the output of digital signals to control the window scanning for PHA acquisition and stepper motor movement of the spectrometer used the multifunctional device model USB-6008 commanded by the graphical programming language LabVIEW, both from National Instruments. One of the programs performs a pulse height analysis (PHA) and the other is responsible for X-ray photon counting based on the serial movement of the crystal/detector. Additional achievements included assembling the counting electronics and retrieving and modifying the original detector. The bench tests were performed using a radioactive source of 57Co for photon production. The PHA spectrum acquired using a sealed detector showed well defined peaks at 6.4 keV (Fe Kα) and 14.4 keV (gamma emission), as expected from the literature. The acquisition of PHA spectrum using a flow detector defined the baseline and window voltage for selection of pulses related to Fe Kα. Using these parameters, the scanning of crystal/detector pair showed the Fe Kα peak at the expected position

Virtual Mössbauer Spectrometer in the PXI Modular System

A virtual instrumentation programming method has been used for building a computer-based Mössbauer spectrometer. Data acquisition is realized via two PXI or PCI commercially available modules, the digital oscilloscope NI 5102 and the function generator NI 5401 (National Instruments), which are supported by relevant software drivers. Virtual Mössbauer spectrometer is implemented by the graphical programming language LabVIEW 7 Express. The RTSI bus is used for a synchronization of the registration of gamma ray photons with a relative velocity of the motion between the radioactive source and the sample. The amplitude selection of the impulses from the detector output is carried out by an assistance of the Waveform Peak Detection.vi function. The sampling rate of the detector output signal and frequency of the velocity signal determine the number of registration channels of the measured Mössbauer spectrum

Optoelectronics – Devices and Applications

Optoelectronics - Devices and Applications is the second part of an edited anthology on the multifaced areas of optoelectronics by a selected group of authors including promising novices to experts in the field. Photonics and optoelectronics are making an impact multiple times as the semiconductor revolution made on the quality of our life. In telecommunication, entertainment devices, computational techniques, clean energy harvesting, medical instrumentation, materials and device characterization and scores of other areas of R&D the science of optics and electronics get coupled by fine technology advances to make incredibly large strides. The technology of light has advanced to a stage where disciplines sans boundaries are finding it indispensable. New design concepts are fast emerging and being tested and applications developed in an unimaginable pace and speed. The wide spectrum of topics related to optoelectronics and photonics presented here is sure to make this collection of essays extremely useful to students and other stake holders in the field such as researchers and device designers