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In the differential x‐ray diffraction (DXRD) method the diffraction pattern for iron minerals in a soil or clay sample is obtained by subtracting the pattern for a sample free of iron oxides, after appropriate adjustment of intensity, from that of an untreated sample. We modified this method by using 1 µm α‐alumina as an internal standard to calculate the scale factor for the adjustment of intensity. The internal standard also serves as a reference for making corrections in peak position. Alumina has the advantages that it is not attacked by the citrate‐bicarbonate‐dithionite (CBD) treatment to remove iron oxides and its peak positions do not overlap the broad diffraction peaks of Fe oxides in the range of 2 to . The effects of CBD treatment on soil components other than Fe oxides can also be observed. Iron minerals in 11 soils from Indiana and Goias State, Brazil, were characterized using this technique. Hematitegoethite ratios, mean crystallite dimension, and amount of Al substitution in the iron oxides were calculated from the position, height, and width at half‐height of the DXRD peaks. The redder soils had more extractable Fe and larger hematite‐goethite ratios than the yellower soils. The amount of Al substitution in goethite and hematite and the mean crystallite dimension of hematite was greater for the Oxisols of Brazil than the Alfisols of Indiana. Maghemite was detected in soil clay of a red Oxisol from Brazil.

A potentiostat/galvanostat with wireless data transmission and a GPS receiver was applied to in situ flow analyses.

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This work describes the development of a system designed to measure important operational parameters of mammography equipment, as kVp, tube current, exposure time, dose and half-value layer (HVL) in any field location. This system is based on a device with a Si semiconductor sensor, placed under the X-ray tube (over the unit table, for example), which detects the X-ray photons, yielding an electric current proportional to the beam intensity. This signal is driven to a digitizer card coupled to a notebook where a software provides the signal reading and treatment. The kVp measurement is based on the ratio of two signals, one filtered and other non-filtered (reference) from the same sensor. This kind of signal is obtained by detecting the sensor output during the X-ray exposure with a circular shaped aluminum wedge rotating over it. With a single exposure, the software allows to determine the actual parameters by this signal analysis. In addition, HVL in any field location can be determined by a previous developed computer simulation procedure. Calibration curves are stored so that the software compares the actual reading from the sensor X-ray exposures with the stored data to determine how accurate the tube under investigation is working. Development tests with a Trex Medical Contour 2000 unit have shown that the system response is in agreement with calibrated devices used for checking the parameters. An advantage of this system is the possibility of storing a lot of information requested for quality assurance programs. ResumoEsse trabalho descreve o desenvolvimento de um sistema para medição de importantes parâmetros operacionais de equipamentos mamográficos, como kVp, corrente de tubo, tempo de exposição, dose e camada semi-redutora (CSR) em qualquer posição do campo. Esse sistema baseia-se num dispositivo com sensor semicondutor de Si, posicionado sob o tubo de raios X (sobre a mesinha do equipamento, por exemplo), que detecta os fótons e produz uma corrente elétrica proporcional à intensidade do feixe. Esse sinal é enviado a uma placa digitalizadora acoplada a um notebook no qual um software realiza sua leitura e tratamento. A medição da kVp se baseia na relação entre dois sinais, um filtrado e outro não (referência) a partir do mesmo sensor. Esse sinal é obtido detectando-se a saída do sensor sobre o qual gira uma cunha de alumínio circular durante uma exposição de raios X. Com uma única exposição, o software permite determinar os parâmetros pela análise desse sinal. Além disso, a CSR em qualquer posição do campo pode ser determinada a partir de um procedimento de simulação computacional desenvolvido previamente. Curvas de calibração são armazenadas para que o software compare a leitura real do sensor com os dados armazenados para determinar a precisão de operação do tubo sob investigação. Testes de desenvolvimento com uma unidade Trex Medical Contour 2000 mostraram que a resposta do sistema é concordante com dispositivos calibrados usados para verificar os parâmetros. Uma vantagem desse sistema é a possibili...