Polarimetry in X- and Gamma-Ray Astronomy: The Ultimate Dimension

Polarization has been a powerful diagnostic tool in radio, microwave, and visible astronomy, providing details of photonproduction mechanisms on much smaller scales than can bedirectly imaged or deduced from photon intensity and energyalone. While polarimetry at other these wavebands (radio,microwave, and optical) is an established technique, highenergy astrophysics lags far behind in this respect. Yet polarizationanalysis has the potential of revealing many detailsabout the magnetic fields, geometries, and emission mechanismsfound in high energy emitting sources. Deviations fromspherical symmetry and/or the presence of ordered magneticfields give rise to polarized radiation: some examples includeanisotropy in solar flares, the presence of jets in microquasarsand blazars, accretion disks around stellar and massive blackholes, accreting and rotation-powered pulsars, and beams ingamma-ray bursts. In addition, null polarization detectionsfrom gamma-ray bursts at x-ray energies have been usedas a test of fundamental physics by placing limits on the possibleviolation of Lorentz invariance

Results of the simulations of the petal/lens as part of the LAUE project

In the context of the LAUE project for focusing hard X-/gamma rays, a petal of the complete lens is being assembled at the LARIX facility in the Department of Physics and Earth Science of the University of Ferrara. The lens petal structure is composed of bent Germanium and Gallium Arsenide crystals in transmission geometry. We present the expectations derived from a mathematical model of the lens petal. The extension of the model for the complete LAUE project in the 90 -- 600 keV energy range will be discussed as well. A quantitative analysis of the results of these simulations is also presented.Comment: 12 pages, 26 figures, SPIE optics + Photonics conference 2013, Vol: 886

Charge Correction in X and Gamma Ray Detectors Based on CZT

CZT, show some prerogatives as materials for X and gamma ray detection because of its properties, as high stopping power, good transport properties, and low leakage current even at room temperature. Nevertheless, despite the improvement in the grown techniques, its transport properties are limited, if compared with those of traditional materials for radiation detection. This fact leads to a reduction of spectroscopic properties especially when increases the penetration length of gamma-rays at high energies. Several methods have been proposed to link the interaction depth and the charge losses achieving good improvements in the spectroscopy but, in most cases, they produce only heuristic corrections without any clearly visible relation with some physical models. Bargholtz et al. have improved the spectroscopy digitizing the signals and fitting them with a model, but this method is very expensive in term of computing power because of the high number of fitting paramiters. In this work, we propose an hybrid approach to the problem. Once known the read-out electronic transfer function, the detector signal could be corrected using the photon impact depth (extracted from the discontinuity in the current signal) and the material transport parameters, obtained from two simple fitting procedure with only four free parameters for each fit. This method, based on the Zanio model, is not only useful to correct the charge losses but also to achieve the characteristic properties of CZT, because takes into account also the detrapping contribution. In the last year we have presented the results obtained with a simplified model, now we show those obtained with the complete model, with a more accurate fit that lead to a more precise measure of detrapping time. The transfer function used in the calculations is the one measured in our system; nevertheless the procedure employed and the calculation of the integral terms are immediately extendable to many other transfer function

CdTe/CZT spectrometers with 3-D imaging capabilities

Semiconductor detector technology has dramatically changed the broad field of x-ray and ?-ray spectroscopy and imaging. Semiconductor detectors, originally developed for particle physics applications, are now widely used for x/?-ray spectroscopy and imaging in a wide variety of fields, including, for example, x-ray fluorescence, ?-ray monitoring and localization, noninvasive inspection and analysis, astronomy, and diagnostic medicine. The success of semiconductor detectors is due to several unique characteristics, such as excellent energy resolution, high detection efficiency, and the possibility of development of compact and highly segmented detection systems. Among semiconductor devices, silicon (Si) detectors are the key detectors in the soft x-ray band (15 keV) and will continue to be the first choice for laboratory-based high-performance spectrometers [3]. © 2015 by Taylor & Francis Group, LLC

Forced Waves Propagation in great living Arteries Tissues

Starting from experimental data, this work exploit the similarity of pressure and axial wave’s propagation of both pressure and axial waves in large vessel (e.g., aorta) with the solution of a mathematical model developed to describe the motion of acoustic waves in solid. In particular, we show how the motion parameters derived by fitting the experimental data measured in living dog arteries are related to mechanical properties of the vessel tissue using the same theoretical model. Furthermore, we briefly discuss the consequence on the predicted forced wave motion of inferring from experimental data a phase velocity depending from frequency

Twin shaping filter technique for signals compensation in CZT detectors grown by the vertical bridgman method

CdTe/CdZnTe is a consolidated material to realize detectors for a large variety of applications, such as medical, industrial, and space research. An Italian collaboration, involving the CNR/IMEM and INAF/IASF institutes, was born some years ago with the aim to develop a national capability to produce CZT detectors starting from the material growth to the final detection device. Some important features of these detectors (pulse height, energy resolution, photopeak efficiency) are affected by the charge collection efficiency: the low mobility of the charge carriers (particularly the holes) and trapping/detrapping phenomena can degrade the CdTe/CZT detectors response, depending on the distance between the charge formation position and the collecting electrodes. Several efforts have been made to improve the detection efficiency as well as the energy resolution, using both the optimization of the electrode geometry (drift strip technique, coplanar-grid, small pixel effect) and pulse height compensation methods to overcome the hole trapping problem. We have studied a bi-parametric method that uses a twin pulse shaping active filter to analyze the same signal: one slow, which is proportional to the energy of the photon, and one fast, which depends on the position of the interaction with respect to the collecting electrode. The experimental results obtained with the application of this bi-parametric technique on planar CZT detectors of good quality grown by the Vertical Bridgman method at CNR/IMEM are presented as a function of the bias voltage, photon energy and shaping time pairs

Interface shape control and tellurium inclusion concentration distribution in CdZnTe crystals grown by vertical Bridgman for X-ray detector applications

In spite of the efforts devoted to the task, many problems connected with the growth of CdZnTe (Zn>0) crystals are still unresolved, in particular tellurium inclusion density control, large single crystalline yield, seeding, and interface shape control. Moreover, also the electrical properties of the crystals (high resistivity and mobility-lifetime product) must be taken into account if detector performances have to be improved. In this work, the authors report on the growth and characterization of several CdZnTe crystals (Zn=10%) by vertical Bridgman, with and without the use of boron oxide as encapsulant. Different techniques were used to characterize the crystals: i) PL mapping for determining interface shape and to study the nucleation ii) a novel IR mapping apparatus to obtain fully 3D reconstruction of the inclusion distribution iii) X-ray detector characterization by means of nuclear sources to study the transport properties of the material (with mobility-lifetime product for electrons up to 6x10-3 cm2/V)

Progress in the Development of CdTe and CdZnTe Semiconductor Radiation Detectors for Astrophysical and Medical Applications

Over the last decade, cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) wide band gap semiconductors have attracted increasing interest as X-ray and gamma ray detectors. Among the traditional high performance spectrometers based on silicon (Si) and germanium (Ge), CdTe and CdZnTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact and reliable detection systems. In this paper, we review the current status of research in the development of CdTe and CdZnTe detectors by a comprehensive survey on the material properties, the device characteristics, the different techniques for improving the overall detector performance and some major applications. Astrophysical and medical applications are discussed, pointing out the ongoing Italian research activities on the development of these detectors

Spectroscopic response of CZT detectors obtained by the boron encapsulated vertical Bridgman method

The purpose of this paper is to present the spectral response at different energies of some CZT crystals grown with the boron oxide encapsulated vertical Bridgman method by IMEM-CNR. The most important feature of the technique is that the crystal, during the growth, is fully encapsulated by a thin layer of liquid boron oxide, so that the crystal-crucible contact is prevented. Using this material, several detectors were realized of about 4x4x1 mm3 in size and with electrical gold contacts on both the surfaces obtained by two different techniques: vacuum vaporization deposition and electroless