Detecting hard X-rays and γ-rays with high energy resolution is critical for medical and industrial applications, high-energy fundamental physics, and homeland security. Two types of radiation detectors, indirect-conversion (scintillators) and direct-conversion (solid-state) detectors, are the most widely used technologies. Semiconductor-based detectors that can directly convert γ-rays into an electrical signal and operate at room temperature are especially important as portable and cost-efficient detectors with high sensitivity and energy resolution. Recently, lead halide perovskites have attracted enormous interest for γ-ray detection, and significant progress has been made toward practical detectors using perovskites as active materials. In this Review, we start with the fundamentals of γ-ray detection and review the recent developments in halide perovskite γ-ray detectors. The key factors affecting the detector performance are summarized. We also give an outlook on the field, with emphasis on the challenges to be overcome. 

Recent Progress in Halide Perovskite Radiation Detectors for Gamma-Ray Spectroscopy

Industrial tomography using three different gamma ray

Mercuric iodide (HgI/sub 2/) is a semiconductor material of interest for use as a gamma ray detector because of its wide band-gap and high atomic number. The current work is with detectors of intermediate thickness (2-5mm), to be used to get good energy resolution with some reasonable gamma ray efficiency. The work reported covers the parallel pulse processing to obtain interaction depth information which is used to extend the usable thickness through resolution enhancements, and to obtain better detector performance from selected portions of the thicker detectors through pulse rejection techniques. A sample spectrum from a 2.5-mm-thick detector is shown. Resolution is about 10% and peak-to-valley ratio about 4:1. After taking advantage of the enhancement techniques described, resolution of 5% and peak-to-valley ratios of 8:1 are common. Poor hole mobility has been used to advantage to obtain interaction depth information. Two techniques are demonstrated for extracting conventional energy spectra from two-parameter spectra - the spectral enhancement technique which corrects for hole losses in every interaction in the detector and increases the number which fall under the full energy peak, and the pulse rejection technique which selects only those pulses which need no correction. (LEW)

Parallel pulse processing for mercuric iodide gamma-ray detectors

Gamma-ray Computed Tomography is an important tool for accessing the internal details of large objects in different industries such as oil, gas, petrochemical, etc. In this paper, a Geant4 study was performed to develop a new approach for this type of tomography by using high aspect ratio scintillators . In this method, a NaI(Tl) rectangular cube scintillator, coupled to a PMT on each side in a coincidence setup, was considered as a position sensitive detector. Different responses of the detector including the scintillation processes in presence of 662 keV gamma-rays of a Cs-137 were simulated. Spectral response , position and energy resolutions were obtained and compared to the experimental data. The comparisons showed a good agreement between the simulation results and experimental data. Furthermore, the detector was simulated in a gamma-ray tomography setup and the related projections and cross sectional images of a standard phantom were obtained. The obtained results showed that the high aspect ratio scintillator detector can be used instead of array detector in industrial applications where there is no need to very high position resolutions.

Industrial gamma computed tomography using high aspect ratio scintillator detectors (A Geant4 simulation)

Nowadays, the application of advanced technologies in modern production systems is the main trend of development and technological progress in many industrial sectors. It is due to the still growing trends of energy-saving and production quality enhancement. Wherever in the production process the phase mixture is transported and it is not optimal or not economic, there is a need to develop a system which would be able to prevent any construction disaster, unexpected production line stopping or situation where for reasons of bad flow parameters, the final product is defective. This paper studies various sensors, measurement techniques and computer methods for signal processing and analysis to diagnose and control two-phase flows. Due to the possibility that the invasive measurement disturbs the process and changes it parameters and behavior especially in the location just after the measurement point and simultaneously does not provide any information about these changes it is unreliable for the diagnosis or control. Therefore, the non-invasive techniques commonly used for measurement of flows parameters are described. Depending on the industrial demands many of applications examples for non-invasive two-phase flows measurement and monitoring are given. This description for identifying the flow parameters is divided into features categories of this phenomena as void fraction distribution, velocity profile and flow regime. However, from these methods the high accuracy and short processing time is expected. The continued observation and monitoring of the process abnormalities can provide valuable information about its dynamic state and allow for real-time and automatic monitoring and control. Therefore, the development of advanced process control is one of the most important challenges to keep the flow regime on the given level and for instant and long-term energy saving, quality improvement.

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Computer methods for non-invasive measurement and control of two-phase flows: a review study

Gamma-ray tomography experiments have been carried out to detect spatial patterns in the porosity, in a 0.27 m diameter packed steel column using a first generation computed tomography (CT) system. The CT scanner consists of a NaI(Tl) detector 5.08 cm in diameter, and an encapsulated 137 Cs (3.7 GBq) radioactive source, located opposite to the center of the detector. The detector and the source, mounted on a fixed support and the column, can rotated and dislocate by two stepping motors controlled through a microprocessor. Different sizes of stainless steel Raschig rings (12.6, 37.9 and 76 mm) have been examined. The primary objective of this work is to detect spatial patterns and statistical information on porosity variation in packed distillation columns. Horizontal scans, at different vertical positions of the packed bed were made for each size of Raschig rings. Radial porosity variation within the packed bed has been determined. This study has demonstrated that the porosity and its spatial distribution in a metallic packed column can be measured with adequate spatial resolution using the gamma-ray tomography technique. After validation of this first generation CT, the turntable design to rotate and dislocate the 60 Co or 137 Cs sealed gamma-ray sources and multidetector array for the third generation industrial computed tomography was also developed.

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Gamma-ray computed tomography SCANNERS for applications in multiphase system COLUMNs*

A portable tomography system with seventy detectors and five gamma-ray sources in fan beam geometry simulated by Monte Carlo method

In this work, the establishment of a technique for HgI growth and preparation of crystals, for use as room temperature radiation semiconductor detectors is described. Three methods of crystal growth were studied while developing this work: (1) Physical Vapor Transport (PVT); (2) Saturated Solution of HgI2, using two different solvents; (a) dimethyl sulfoxide (DMSO) and (b) acetone, and (3) the Bridgman method. In order to evaluate the obtained crystals by the three methods, systematic measurements were carried out for determining the stoichiometry, structure, orientation, surface morphology and impurity of the crystal. The influence of these physical chemical properties on the crystals development was studied, evaluating their performance as radiation detectors. The X-ray diffractograms indicated that the crystals were, preferentially, oriented in the (001) e (101) directions with tetragonal structure for all crystals. Nevertheless, morphology with a smaller deformation level was observed for the crystal obtained by the PVT technique, comparing to other methods. Uniformity on the surface layer of the PVT crystal was detected, while clear incrustations of elements distinct from the crystal could be viewed on the DMSO crystal surface. The best results as to radiation response were found for the crystal grown by physical vapor transport. Significant improvement in the HgIz2 radiation detector performance was achieved for purer crystals, growing the crystal twice by PVT technique. SUMÁRIO 1. Introdução .......................................................................................................................... 8 2. Considerações teóricas ..................................................................................................... 12 2.1. Detectores semicondutores ........................................................................................... 12 2.1.1. Teoria das bandas de energia ..................................................................................... 13 2.1.2. Detectores semicondutores que operam a temperatura ambiente .............................. 14 2.2. Iodeto de mercúrio (HgI2) ............................................................................................. 16 2.3. Crescimento de cristais ................................................................................................. 18 2.3.1. Crescimento por fusão ............................................................................................... 18 2.3.2. Crescimento por epitaxia ........................................................................................... 18 2.3.3. Crescimento por solução saturada ............................................................................. 19 2.4. Radiação ionizante ........................................................................................................ 20 2.4.1. Interação da radiação gama ou x com a matéria ........................................................ 20 2.4.1.1. Efeito fotoelétrico ................................................................................................... 22 2.4.1.2. Efeito compton ........................................................................................................ 22 2.4.1.3. Produção de pares ................................................................................................... 23 2.4.2. Interação das partículas radioativas carregadas com a matéria ................................. 24 3. Objetivos .......................................................................................................................... 26 4. Materiais e métodos ......................................................................................................... 27 4.1. Crescimento de cristais ................................................................................................. 27 4.1.2 crescimento de cristais pelo método bridgman ........................................................... 27 4.1.3. Crescimento em solução saturada .............................................................................. 28 4.1.4. Crescimento por transporte físico de vapor (pvt) ...................................................... 32 4.2. Caracterização físico química do cristal de HgI2 .......................................................... 34 4.2.1. Difração de raios-x ..................................................................................................... 34 4.2.2. Microscopia eletrônica de varredura (mev) ............................................................... 34 4.2.3. Espectrometria de massas com plasma (icp-ms) ....................................................... 36 4.2.4. Determinação da energia de banda proibida .............................................................. 37 5. Avaliacao da resposta do cristal como detector de radiação............................................. 39 5.1. Preparação dos contactos elétricos. .............................................................................. 39 5.2 medidas da resistividade e da corrente de fuga do detector ........................................... 39 5.3. Resposta do detector de radiação. ................................................................................. 40 5.3.1 resposta à radiação ...................................................................................................... 40 6. Resultados e discussões .................................................................................................... 41 6.1 aspectos visuais dos cristais ........................................................................................... 41 6.2 difração de raios-x ......................................................................................................... 44 6.3. Espectrometria de massas com plasma (icp-ms) .......................................................... 45 6.4 microscopia eletrônica de varredura (mev) ................................................................... 45 6.4.1 microscopia eletrônica de varredura com elétrons secundários (mev-se) .................. 45 6.4.2 microscopia eletrônica de varredura com elétrons retro espalhados (mev-bse) ......... 47 6.5. Valor da energia da banda proibida .............................................................................. 54 6.6. Avaliação da resposta dos cristais de HgI2 como detectores de radiação ..................... 57 6.6.1. Medidas de corrente em função da tensão aplicada ao detector ................................ 57 6.6.2. Resposta à radiação .................................................................................................... 58 7. Conclusão ......................................................................................................................... 61 8. Apêndices ......................................................................................................................... 63 APÊNDICE A roteiro experimental do crescimento de cristais de HgI2 por transporte físico de vapor – pvt ............................................................................................................. 63 APÊNDICE B roteiro experimental do crescimento de cristais de HgI2 por solução saturada de acetona e iodeto de potássio ............................................................................. 67 APÊNDICE C roteiro experimental do crescimento de cristais de HgI2 por solução saturada de dimetilsulfóxido (dmso) .................................................................................... 70 APÊNDICE D roteiro experimental do crescimento de cristais de HgI2 pelo método de bridgman .............................................................................................................................. 72 referências bibliográficas ..................................................................................................... 75

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Desenvolvimento do cristal semicondutor de iodeto de mercúrio para aplicação como detector de radiação

This work describes a multi-source computed tomography It showed to be a feasible tool to study multiphase systems In this CT scanner, two different radioactive sources, 192Ir and 137Cs, were placed together into a single lead collimated system The CT is capable to determine and differentiate the attenuation coefficients of materials constituted of three phases (gas, liquid and solid), using two or more different radioisotope energies

Joao F. T. Martins

Papers

Industrial tomography using three different gamma ray

Gamma-ray computed tomography SCANNERS for applications in multiphase system COLUMNs*

A portable tomography system with seventy detectors and five gamma-ray sources in fan beam geometry simulated by Monte Carlo method

Desenvolvimento do cristal semicondutor de iodeto de mercúrio para aplicação como detector de radiação

Multi-source third generation computed tomography for industrial multiphase flows applications