137 research outputs found
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)
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
A focal plane detector design for a wide-band Laue-lens telescope
The energy range above 60 keV is important for the study of many open
problems in high energy astrophysics such as the role of Inverse Compton with
respect to synchrotron or thermal processes in GRBs, non thermal mechanisms in
SNR, the study of the high energy cut-offs in AGN spectra, and the detection of
nuclear and annihilation lines. Recently the development of high energy Laue
lenses with broad energy bandpasses from 60 to 600 keV have been proposed for a
Hard X ray focusing Telescope (HAXTEL) in order to study the X-ray continuum of
celestial sources. The required focal plane detector should have high detection
efficiency over the entire operative range, a spatial resolution of about 1 mm,
an energy resolution of a few keV at 500 keV and a sensitivity to linear
polarization. We describe a possible configuration of the focal plane detector
based on several CdTe/CZT pixelated layers stacked together to achieve the
required detection efficiency at high energy. Each layer can operate both as a
separate position sensitive detector and polarimeter or work with other layers
to increase the overall photopeak efficiency. Each layer has a hexagonal shape
in order to minimize the detector surface required to cover the lens field of
view. The pixels would have the same geometry so as to provide the best
coupling with the lens point spread function and to increase the symmetry for
polarimetric studies.Comment: 10 pages, 9 figure
Charge Transport Properties in CZT Detectors Grown by the Vertical Bridgman Technique
Great efforts are being presently devoted to the development of CdTe and CdZnTe detectors for a large variety of applications, such as medical, industrial, and space research. We present the spectroscopic properties of some CZT crystals grown by the standard vertical Bridgman method and by the boron oxide encapsulated vertical Bridgman method, which has been recently implemented at IMEM-CNR. By this technique the crystal is grown in an open quartz crucible fully encapsulated by a thin layer of liquid boron oxide. This technique prevent the crystal-crucible contact allowing larger single grains with lower dislocation density to be obtained. Several mono-electrode detectors were realized with two planar gold contacts. The samples are characterized by an active area of ≈4x4 mm2 or ≈7x7 mm2 and with thickness ranging from 1 to 2 mm. The charge transport properties of the detectors have been studied by mobility-lifetime (μτ) product measurements, carried out at the European Synchrotron Radiation Facility (Grenoble) in PTF configuration, where the impinging beam direction is orthogonal to the collecting electric field. We have performed several fine scans between the electrodes with a beam spot of 10x10 μm2 at different energies from 60 keV to 400 keV. In this work we present the test results in terms of μτ product of both charge carriers and an evaluation of the spectroscopic response uniformity across the sensitive volume of tested samples
Signal compensation in CZT detectors grown by the Vertical Bridgman method using a twin-shaping filter technique
CdTe/CZT is now a material consolidated for the detectors realization operating at room temperature, which find a large variety of applications in astrophysics, medical imaging and security. An Italian collaboration, involving the CNR/IMEM and INAF/IASF institutes, was born several years ago with the aim to develop a national capability to produce CZT detectors starting from the material growth to the final detection device. The collection efficiency of the charge carriers affects some important features of these detectors, such as the pulse height, energy resolution, photopeak efficiency. In fact the low mobility of the charge carriers (particularly the holes) and trapping/detrapping phenomena can degrade the CdTe/CZT detector response, depending on the distance between the charge formation position and the collecting electrodes. Two kinds of techniques can be used to improve both the collection efficiency and the energy resolution, based on the optimization of the electrode geometry and/or signal compensation methods. We have implemented a biparametric method that uses a twin pulse shaping active filter to analyze the same signal from the detector: one “slow”, which is proportional to the energy of the incident photon, and one “fast”, which depends on the position of the interaction with respect to the collecting electrode. We present this biparametric technique applied on planar CZT detectors grown by the Vertical Bridgman method at CNR/IMEM (Parma), the experimental results obtained as a function of the bias voltage, photon energy, shaping time pairs and the compensated spectra
Imaging performance above 150 keV of the wide field monitor on board the ASTENA concept mission
A new detection system for X-/Gamma-ray broad energy passband detectors for
astronomy has been developed. This system is based on Silicon Drift Detectors
(SDDs) coupled with scintillator bars; the SDDs act as a direct detector of
soft (<30 keV) X-ray photons, while hard X-/Gamma-rays are stopped by the
scintillator bars and the scintillation light is collected by the SDDs. With
this configuration, it is possible to build compact, position sensitive
detectors with unprecedented energy passband (2 keV - 10/20 MeV). The X and
Gamma-ray Imaging Spectrometer (XGIS) on board the THESEUS mission, selected
for Phase 0 study for M7, exploits this innovative detection system. The Wide
Field Monitor - Imager and Spectrometer (WFM-IS) of the ASTENA (Advanced
Surveyor of Transient Events and Nuclear Astrophysics) mission concept consists
of 12 independent detection units, also based on this new technology. For the
WFM-IS, a coded mask provides imaging capabilities up to 150 keV, while above
this limit the instrument will act as a full sky spectrometer. However, it is
possible to extend imaging capabilities above this limit by alternatively
exploiting the Compton kinematics reconstruction or by using the information
from the relative fluxes measured by the different cameras. In this work, we
present the instrument design and results from MEGAlib simulations aimed at
evaluating the effective area and the imaging performances of the WFM-IS above
150 keV
The TRILL project: increasing the technological readiness of Laue lenses
Hard X-/soft Gamma-ray astronomy (> 100 keV) is a crucial field for the study
of important astrophysical phenomena such as the 511 keV positron annihilation
line in the Galactic center region and its origin, gamma-ray bursts, soft
gamma-ray repeaters, nuclear lines from SN explosions and more. However,
several key questions in this field require sensitivity and angular resolution
that are hardly achievable with present technology. A new generation of
instruments suitable to focus hard X-/soft Gamma-rays is necessary to overcome
the technological limitations of current direct-viewing telescopes. One
solution is using Laue lenses based on Bragg's diffraction in a transmission
configuration. To date, this technology is in an advanced stage of development
and further efforts are being made in order to significantly increase its
technology readiness level (TRL). To this end, massive production of suitable
crystals is required, as well as an improvement of the capability of their
alignment. Such a technological improvement could be exploited in stratospheric
balloon experiments and, ultimately, in space missions with a telescope of
about 20 m focal length, capable of focusing over a broad energy pass-band. We
present the latest technological developments of the TRILL (Technological
Readiness Increase for Laue Lenses) project, supported by ASI, devoted to the
advancement of the technological readiness of Laue lenses. We show the method
we developed for preparing suitable bent Germanium and Silicon crystals and the
latest advancements in crystals alignment technology.Comment: arXiv admin note: text overlap with arXiv:2211.1688
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