Thermoluminescence characteristics of rare-earth-doped LiCaBO3 phosphor

LiCaBO3 was synthesized by high-temperature solid-state reaction. The influence of different rare earth dopants, i.e. Dy3+, Tb3+. TM3+ and Ce3+, on thermoluminescence (TL) of LiCaBO3 phosphor was discussed. We studied the TL properties and some dosimetric characteristics of Ce3+-activated LiCaBO3 phosphor in detail. The effect of the concentration of Ce3+ on TL was investigated, the result of which showed that the optimum Ce3+ concentration was 1 mol%. The TL kinetic parameters of LiCaBO3:0.01 Ce3+ were studied by computer glow curve deconvolution (CGCD) method.

Thermoluminescence characteristics of NaSr4(BO3)(3):Ce3+ under beta-ray irradiation

The thermoluminescence (TL) properties of Ce3+ doped NaSr4(BO3)(3) phosphor under the beta-ray irradiation were reported. The polycrystalline sample was synthesized by high temperature solid-state reaction. The TL glow curve of NaSr4(BO3)(3):Ce3+ phosphor was composed of only one peak. TL kinetic parameters of NaSr4(BO3)(3):Ce3+ were deduced by the peak shape method, the activation energy (E) was 0.590 eV and the frequency factor was 1.008x10(6) s(-1). TL dose response was linear in the range of measurement. The 3-dimensional (3D) TL emission spectrum was also recorded, the emission spectrum consisted of two bands located at 441 and 479 nm respectively, corresponding to the characteristic 4f(0)5d(1)-> F-2((5/2,7/2)) transitions of the Ce3+ ion. The fading behavior of the NaSr4(BO3)(3):Ce3+ phosphor over a period of 15 d was also studied.

Quantum trajectories for the realistic measurement of a solid-state charge qubit

We present a new model for the continuous measurement of a coupled quantum dot charge qubit. We model the effects of a realistic measurement, namely adding noise to, and filtering, the current through the detector. This is achieved by embedding the detector in an equivalent circuit for measurement. Our aim is to describe the evolution of the qubit state conditioned on the macroscopic output of the external circuit. We achieve this by generalizing a recently developed quantum trajectory theory for realistic photodetectors [P. Warszawski, H. M. Wiseman, and H. Mabuchi, Phys. Rev. A 65, 023802 (2002)] to treat solid-state detectors. This yields stochastic equations whose (numerical) solutions are the realistic quantum trajectories of the conditioned qubit state. We derive our general theory in the context of a low transparency quantum point contact. Areas of application for our theory and its relation to previous work are discussed.

X-ray computed tomography

X-ray computed tomography (CT) is a medical imaging technique that produces images of trans-axial planes through the human body. When compared with a conventional radiograph, which is an image of many planes superimposed on each other, a CT image exhibits significantly improved contrast although this is at the expense of reduced spatial resolution.----- A CT image is reconstructed mathematically from a large number of one dimensional projections of the chosen plane. These projections are acquired electronically using a linear array of solid-state detectors and an x ray source that rotates around the patient.----- X-ray computed tomography is used routinely in radiological examinations. It has also be found to be useful in special applications such as radiotherapy treatment planning and three-dimensional imaging for surgical planning.

Development of a single photon counting computed tomography system using MPGDs

The development of computed tomography systems with energy resolving detectors is a current challenge in medical physics and biomedical engineering. A computed tomography system of this kind allows getting complementary informations relatively to conventional systems, that can help the medical diagnosis, being of great interest in medicine. The work described in this thesis is related to the development of a computed tomography system using micropattern gaseous detectors, which allow storing, simultaneously, information about the interaction position and the energy of each single photon that interacts with the detector. This kind of detectors has other advantages concerning the cost and characteristics of operation when compared with solid state detectors. Tomographic acquisitions were performed using a MicroHole & Strip Plate based detector, which allowed reconstructing cross-sectional images using energy windows, applying the energy weighting technique and performing multi-slice and tri-dimensional reconstructions. The contrast-to-noise ratio was improved by 31% by applying the energy weighting technique, comparing with the corresponding image obtained with the current medical systems. A prototype of a computed tomography with flexibility to change the detector was developed, making it possible to apply different detectors based on Thick-COBRA. Several images acquired with these detectors are presented and demonstrate their applicability in X-ray imaging. When operating in NeCH4, the detector allowed a charge gain of 8 104, an energy resolution of 20% (full width at half maximum at 8 keV), a count rate of 1 106 Hz/mm2, a very stable operation (gain fluctuations below 5%) and a spacial resolution of 1.2 mm for an energy photon of 3.6 keV. Operating the detector in pure Kr allowed increasing the detection efficiency and achieving a charge gain of 2 104, an energy resolution of 32% (full width at half maximum at 22 keV), a count rate of 1 105 Hz/mm2, very stable operation and a spatial resolution of 500 m. The software already existing in the group was improved and tools to correct geometric misalignments of the system were also developed. The reconstructions obtained after geometrical correction are free of artefacts due to the referred misalignments.

Commissioning and performance of the CMS silicon strip tracker with cosmic ray muons

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

The CMS experiment at the CERN LHC

The Compact Muon Solenoid (CMS) detector is described. The detector operates at the Large Hadron Collider (LHC) at CERN. It was conceived to study proton-proton (and lead-lead) collisions at a centre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and at luminosities up to 10(34)cm(-2)s(-1) (10(27)cm(-2)s(-1)). At the core of the CMS detector sits a high-magnetic-field and large-bore superconducting solenoid surrounding an all-silicon pixel and strip tracker, a lead-tungstate scintillating-crystals electromagnetic calorimeter, and a brass-scintillator sampling hadron calorimeter. The iron yoke of the flux-return is instrumented with four stations of muon detectors covering most of the 4 pi solid angle. Forward sampling calorimeters extend the pseudo-rapidity coverage to high values (vertical bar eta vertical bar <= 5) assuring very good hermeticity. The overall dimensions of the CMS detector are a length of 21.6 m, a diameter of 14.6 m and a total weight of 12500 t.

Quantificação da resoluçao do sistema SPECT-CZT através do uso da função de transferência modulada (MTF)

Pós-graduação em Biologia Geral e Aplicada - IBB

Gama Câmara CZT: alteração de paradigmas em aquisição de imagens de medicina nuclear

Nuclear medicine is a medical specialty related to imagery that deals with imaging techniques, diagnosis and therapy, allowing observing the physiological state of tissues noninvasively by marking the molecules participating of these physiological processes with radioactive isotopes, thus creating the called radionuclides. The image of a radionuclide is one of the most important applications of radioactivity in nuclear medicine. The equipment’s of nuclear medicine imaging use the principle of radiation detection, turning it into an electrical signal which, through specific algorithms, allows forming tomographic images that provide information about the functional status of organs. New detection systems have been developed for tomographic acquisitions using solid state detectors. These devices use crystals of cadmium zinc telluride (CdZnTe). Some of the advantages of this detector are a significant improvement of signal to noise ratio, the increased spectral and spatial resolution, which in sum, result in greater clarity of the images obtained, opening new perspectives for imaging protocols previously unattainable. In contrast, all other gamma-cameras equipped with vacuum tubes have remained relatively unchanged for nearly fifty years. In these gamma-cameras, the images are obtained using two steps significantly less efficient: the gamma rays are converted to light through a first device, and then the light is converted into an electrical signal through a second device. One of functions the Medical Physicist is related to the quality control of equipment. This control ensures that the information and images provided are true and thus credible to be used in medical reports. To perform this type of analysis the physicist must understand the performance characteristics and operation of all equipment of the department concerned; besides, in the absence of specific legislation, proposing...(Complete abstract click electronic access below)

The STEREO/PLASTIC response to solar wind ions (Flight measurements and models)

The Plasma and Supra-Thermal Ion Composition (PLASTIC) instrument is one of four experiment packages on board of the two identical STEREO spacecraft A and B, which were successfully launched from Cape Canaveral on 26 October 2006. During the two years of the nominal STEREO mission, PLASTIC is providing us with the plasma characteristics of protons, alpha particles, and heavy ions. PLASTIC will also provide key diagnostic measurements in the form of the mass and charge state composition of heavy ions. Three measurements (E/qk, time of flight, ESSD) from the pulse height raw data are used to characterize the solar wind ions from the solar wind sector, and part of the suprathermal particles from the wide-angle partition with respect to mass, atomic number and charge state. In this paper, we present a new method for flight data analysis based on simulations of the PLASTIC response to solar wind ions. We present the response of the entrance system / energy analyzer in an analytical form. Based on stopping power theory, we use an analytical expression for the energy loss of the ions when they pass through a thin carbon foil. This allows us to model analytically the response of the time of flight mass spectrometer to solar wind ions. Thus we present a new version of the analytical response of the solid state detectors to solar wind ions. Various important parameters needed for our models were derived, based on calibration data and on the first flight measurements obtained from STEREO-A. We used information from each measured event that is registered in full resolution in the Pulse Height Analysis words and we derived a new algorithm for the analysis of both existing and future data sets of a similar nature which was tested and works well. This algorithm allows us to obtain, for each measured event, the mass, atomic number and charge state in the correct physical units. Finally, an important criterion was developed for filtering our Fe raw flight data set from the pulse height data without discriminating charge states.

Estudio del radón en viviendas mediante modelos de minería de datos basados en cubos OLAP

En esta tesis doctoral se estudian las variaciones de radón en el interior de dos viviendas similares de construcción nueva en Madrid, una de ellas ocupada y la otra no, que forman parte del mismo edificio residencial. La concentración de radón y los parámetros ambientales (presión, temperatura y humedad) se midieron durante ocho meses. La monitorización del gas radón se realizó mediante detectores de estado sólido. Simultáneamente, se adquirieron algunas variables atmosféricas de un modelo atmosférico. En el análisis de los datos, se utilizó principalmente el método de la Transformada Wavelet. Los resultados muestran que el nivel de radón es ligeramente más alto en la vivienda ocupada que en la otra. A partir del análisis desarrollado en este estudio, se encontró que había un patrón específico estacional en la concentración de radón interior. Además, se analizó también la influencia antropogénica. Se pudieron observar patrones periódicos muy similares en intervalos concretos sin importar si la vivienda está ocupada o no. Por otra parte, los datos se almacenaron en cubos OLAP. El análisis se realizó usando unos algoritmos de agrupamiento (clustering) y de asociación. El objetivo es descubrir las relaciones entre el radón y las condiciones externas como la presión, estabilidad, etc. Además, la metodología aplicada puede ser útil para estudios ambientales en donde se mida radón en espacios interiores. ABSTRACT The present thesis studies the indoor radon variations in two similar new dwellings, one of them occupied and the other unoccupied, from the same residential building in Madrid. Radon concentration and ambient parameters were measured during eight months. Solid state detectors were used for the radon monitoring. Simultaneously, several atmospheric variables were acquired from an atmospheric model. In the data analysis, the Wavelet Transform Method was mainly used. The results show that radon level is slightly higher in the unoccupied dwelling than in the other one. From the analysis developed in this study, it is found that a specific seasonal pattern exists in the indoor radon concentration. Besides, the anthropogenic influence is also analysed. Nearly periodical patterns could be observed in specific periods whether dwelling is occupied or not. Otherwise, data were stored in cubes OLAP. Analysis was carried out using clustering and association algorithms. The aim is to find out the relationships among radon and external conditions like pressure, stability, etc. Besides, the methodology could be useful to assess environmental studies, where indoor radon is measured.

Study Of Water Flowrate Using Time Transient And Cross-Correlation Techniques With 82br Radiotracer

This paper aims to determinate the water flowrate using Time Transient and Cross-Correlation techniques. The detection system uses two NaI(Tl) detectors adequately positioned on the outside of pipe and a gamma-ray source (82Br radiotracer). The water flowrate measurements using Time Transient and Cross-Correlation techniques were compared to invasive conventional measurements of the flowmeter previously installed in pipeline. Discrepancies between Time Transient and Cross-Correlation techniques flowrate values were found to be less than 3% in relation to conventional ones.

Flow Regime Identification Methodology with Mcnp-X Code And Artificial Neural Network

This paper presents flow regimes identification methodology in multiphase system in annular, stratified and homogeneous oil-water-gas regimes. The principle is based on recognition of the pulse height distributions (PHD) from gamma-ray with supervised artificial neural network (ANN) systems. The detection geometry simulation comprises of two NaI(Tl) detectors and a dual-energy gamma-ray source. The measurement of scattered radiation enables the dual modality densitometry (DMD) measurement principle to be explored. Its basic principle is to combine the measurement of scattered and transmitted radiation in order to acquire information about the different flow regimes. The PHDs obtained by the detectors were used as input to ANN. The data sets required for training and testing the ANN were generated by the MCNP-X code from static and ideal theoretical models of multiphase systems. The ANN correctly identified the three different flow regimes for all data set evaluated. The results presented show that PHDs examined by ANN may be applied in the successfully flow regime identification.