Hard X-ray astronomy is a crucial field for understanding physical processes occurring in several celestial objects, characterized by extreme physical conditions and strong gravity regime, but still poorly explored. Current hard-X ray instrumentation suffers from a poor angular resolution, compared with other wavelengths, and insufficient continuum sensitivity to resolve hard X-ray spectra, especially above few hundreds keV. Laue lenses made with bent crystals represent a viable solution to overcome both limitations, providing good angular resolution ( better than 30 arcsec) combined with excellent sensitivity (orders of magnitude better than that achievable with the current non focusing instrumentation). Supported by the Italian Space Agency, we test a modular method for building Laue lenses. This consists in the realization of portions of Laue lenses that are successively tuned and aligned under the control of a gamma-ray source for focusing the radiation on the common Laue lens focal point. Each module, composed with few tens of crystals, can be realized with an accuracy better than 20 arcsecs with the goal of achieving an overall alignment better than 30 arcsec. In addition, we present a significant improvement in the realization of a large number of bent crystals with the required curvature.
E. Caroli, N. Auricchio, A. Basili, V. Carassiti, F. Cassese, S. Del Sordo, F. Frontera, M. Pecora, L. Recanatesi, F. Schiavone, S. Silvestri, S. Squerzanti, J. Stephen, E. Virgilli
The development of wide band Laue lens imaging technology is challenging, but has important potential applications in hard X- and γ-ray space instrumentation for the coming decades. The Italian Space Agency has funded a project dedicated to the development of a reliable technology to assemble a wide band Laue lens for use in space. The ground support equipment (GSE) for this project was fundamental to its eventual success... The GSE was implemented in a hard X-ray beam line built at the University of Ferrara and had the main purpose of controlling the assembly of crystals onto the Laue lens petal and to verify its final performance. The GSE incorporates the management and control of all the movements of the beam line mechanical subsystems and of the precision positioner (based on a Hexapod tool) of crystals on the petal, as well as the acquisition, storing and analysis of data obtained from the focal plane detectors (an HPGe spectrometer and an X-ray flat panel imager). The GSE is based on two PC’s connected through a local network: one, placed inside the beam line, to which all the movement subsystems and the detector I/O interface and on which all the management and acquisition S/W runs, the other in the control room allows the remote control and implements the offline analysis S/W of the data obtained from the detectors. Herein we report on the GSE structure with its interface with the beam line mechanical system, with the fine crystal positioner and with the focal plane detector. Furthermore we describe the SW developed for the handling of the mechanical movement subsystems and for the analysis of the detector data with the procedure adopted for the correct orientation of the crystals before their bonding on the lens petal support.
The development of new focusing optics based on wide band Laue lenses operating from ~60 keV up to several hundred
keV is particularly challenging. This type of hard X-ray or gamma ray optics requires a high performance focal plane
detector in order to exploit to the best their intrinsic capabilities. We describe a three dimensional (3D) position sensitive
detector prototype suitable as the basic module for a high efficiency Laue lens focal plane detector. This detector
configuration is currently under study for use in a balloon payload dedicated to performing a high significance
measurement of the polarization status of the Crab between 100 and 500 keV. The prototype is made by packing 8 linear
modules, each composed of one basic sensitive unit bonded onto a thin supporting ceramic layer. Each unit is a drift strip
detector based on a CZT crystal, irradiated transversally to the electric field direction. The anode is segmented into 8
detection cells, each comprising one collecting strip and 8 surrounding drift strips. The drift strips are biased by a voltage
divider. The cathode is divided into 4 horizontal strips for the reconstruction of the Z interaction position. The detector
readout electronics is based on RENA-3 ASIC and the data handling system uses a custom electronics based on FPGA to
provide the ASIC setting, the event handling logic, and the data acquisition. This paper mainly describes the components
and the status of the undergoing activities for the construction of the proposed 3D CZT prototype and shows the results
of the electronics tests.
Today it is widely recognised that a measurement of the polarization status of cosmic sources high energy emission is a
key observational parameter to understand the active production mechanism and its geometry. Therefore new
instrumentation operating in the hard X/soft γ rays energy range should be optimized also for this type of measurement.
In this framework, we present the concept of a small high-performance spectrometer designed for polarimetry between
100 and 1000 keV suitable as a stratospheric balloon-borne payload dedicated to perform an accurate and reliable
measurement of the polarization status of the Crab pulsar, i.e. the polarization level and direction. The detector with 3D
spatial resolution is based on a CZT spectrometer in a highly segmented configuration designed to operate as a high
performance scattering polarimeter. We discuss different configurations based on recent development results and
possible improvements currently under study. Furthermore we describe a possible baseline design of the payload, which
can be also seen as a pathfinder for a high performance focal plane detector in new hard X and soft gamma ray focussing
telescopes and/or advanced Compton instruments. Finally we present preliminary data from Montecarlo undergoing
studies to determine the best trade-off between polarimetric performance and detector design complexity.
The paper describes the SIDERALE experiment that was hosted as a piggy back payload on SoRa LDB (Sounding Radar
Long Distance Balloon) mission by the Italian Space Agency (ASI). SIDERALE was aimed at testing a detector for high
energy astrophysics applications based on a 4x4 pixel CZT solid state sensor. An onboard data handling computer, a
mass memory and a power supply units were integrated in SIDERALE. Furthermore an innovative telemetry system BIT
(Bi-directional Iridium Telemetry) was used in order for SIDERALE to be autonomous and independent from the
hosting payload. In the paper a preliminary analysis of flight and scientific data is discussed.
KEYWORDS: Sensors, Prototyping, Electronics, Phase transfer function, Spectroscopy, Telescopes, Crystals, Spectrometers, Analog electronics, Detector development
We report on the development of a 3D position sensitive prototype suitable as focal plane detector for Laue lens
telescope. The basic sensitive unit is a drift strip detector based on a CZT crystal, (~19×8 mm2 area, 2.4 mm thick),
irradiated transversally to the electric field direction. The anode side is segmented in 64 strips, that divide the crystal in 8
independent sensor (pixel), each composed by one collecting strip and 7 (one in common) adjacent drift strips. The drift
strips are biased by a voltage divider, whereas the anode strips are held at ground. Furthermore, the cathode is divided in
4 horizontal strips for the reconstruction of the third interaction position coordinate. The 3D prototype will be made by
packing 8 linear modules, each composed by one basic sensitive unit, bonded on a ceramic layer. The linear modules
readout is provided by a custom front end electronics implementing a set of three RENA-3 for a total of 128 channels.
The front-end electronics and the operating logics (in particular coincidence logics for polarisation measurements) are
handled by a versatile and modular multi-parametric back end electronics developed using FPGA technology.
The importance of hard X-ray astronomy (>10 keV) is now widely recognized. Recently both ESA and NASA have
indicated in their guidelines for the progress of X- and γ-ray astronomy in the next decade the development of new
instrumentation working in the energy range from the keV to the MeV region, where important scientific issues are still
open, exploiting high sensitivity for spectroscopic imaging and polarimetry observations. The development of new
concentrating (e.g. multilayer mirror) telescopes for hard X-rays (10 -100 keV) and focusing instruments based on Laue
lenses operating from ~60 keV up to a few MeV is particularly challenging. We describe the design of a threedimensional
(3D) depth-sensing position sensitive device suitable for use as the basic unit of a high efficiency focal
plane detector for a Laue lens telescope. The sensitive unit is a drift strip detector based on a CZT crystal, (10×10 mm2
area, 2.5 mm thick), irradiated transversally to the electric field direction. The anode is segmented into 4 detection cells,
each comprising one collecting strip and 8 drift strips. The drift strips are biased by a voltage divider, whereas the anode
strips are held at 0 V. The cathode is divided in 4 horizontal strips for the reconstruction of the Z interaction position.
The 3D prototype will be made by packing 8 linear modules, each composed of 2 basic sensitive units, bonded onto a
ceramic layer together with the readout electronics.
The science drivers for a new generation soft gamma-ray mission are naturally focused on the detailed study of
the acceleration mechanisms in a variety of cosmic sources. Through the development of high energy optics in the
energy energy range 0.05-1 MeV it will be possible to achieve a sensitivity about two orders of magnitude better
than the currently operating gamma-ray telescopes. This will open a window for deep studies of many classes of
sources: from Galactic X-ray binaries to magnetars, from supernova remnants to Galaxy clusters, from AGNs
(Seyfert, blazars, QSO) to the determination of the origin of the hard X-/gamma-ray cosmic background, from
the study of antimatter to that of the dark matter. In order to achieve the needed performance, a detector with
mm spatial resolution and very high peak efficiency is needed. The instrumental characteristics of this device
could eventually allow to detect polarization in a number of objects including pulsars, GRBs and bright AGNs. In
this work we focus on the characteristics of the focal plane detector, based on CZT or CdTe semiconductor sensors
arranged in multiple planes and viewed by a side detector to enhance gamma-ray absorption in the Compton
regime. We report the preliminary results of an optimization study based on simulations and laboratory tests,
as prosecution of the former design studies of the GRI mission which constitute the heritage of this activity.
The energy range above 50 keV is important for the study of many open problems in high energy astrophysics such as,
non thermal mechanisms in SNR, the study of the high energy cut-offs in AGN spectra, and the detection of nuclear and
annihilation lines. In the framework of the definition of a new mission concept for hard X and soft gamma ray (GRI-
Gamma Ray Imager) for the next decade, the use of Laue lenses with broad energy band-passes from 100 to 1000 keV is
under study. This kind of instruments will be used for deep study the hard X-ray continuum of celestial sources. This
new telescope will require focal plane detectors with high detection efficiency over the entire operative range, an energy
resolution of few keV at 500 keV and a sensitivity to linear polarization. We describe a possible configuration for the
focal plane detector based on CdTe/CZT pixelated layers stacked together to achieve the required detection efficiency at
high energy. Each layer can either operate as a separate position sensitive detector and a polarimeter or together with
other layers in order to increase the overall full energy efficiency. We report on the current state of art in high Z
spectrometers development and on some activities undergoing. Furthermore we describe the proposed focal plane option
with the required resources and an analytical summary of the achievable performance in terms of efficiency and
polarimetry.
The 10-100 keV region of the electromagnetic spectrum contains the potential for a dramatic improvement in our understanding of a number of key problems in high energy astrophysics. A deep inspection of the universe in this band is on the other hand still lacking because of the demanding sensitivity (fraction of μCrab in the 20-40 keV for 1 Ms integration time) and imaging (≈ 15" angular resolution) requirements. The mission ideas currently being proposed are based on long focal length, grazing incidence, multi-layer optics, coupled with focal plane detectors with few hundreds μm spatial resolution capability. The required large focal lengths, ranging between 8 and 50 m, can be realized by means of extendable optical benches (as foreseen e.g. for the HEXITSAT, NEXT and NuSTAR missions) or formation flight scenarios (e.g. Simbol-X and XEUS). While the final telescope design will require a detailed trade-off analysis between all the relevant parameters (focal length, plate scale value, angular resolution, field of view, detector size, and sensitivity degradation due to detector dead area and telescope vignetting), extreme attention must be dedicated to the background minimization. In this respect, key issues are represented by the passive baffling system, which in case of large focal lengths requires particular design assessments, and by the active/passive shielding geometries and materials. In this work, the result of a study of the expected background for a hard X-ray telescope is presented, and its implication on the required sensitivity, together with the possible implementation design concepts for active and passive shielding in the framework of future satellite missions, are discussed.
Stefano Del Sordo, M. Strazzeri, Gaetano Agnetta, B. Biondo, Filippo Celi, Salvatore Giarrusso, A. Mangano, Francesco Russo, M. Zora, Ezio Caroli, Ariano Donati, Filomena Schiavone, John Stephen, Giulio Ventura, L. Abbene, Francesco Fauci, Giuseppe Raso, Giovanni Pareschi
Cadmium zinc telluride (CZT) pixel detectors show very good
spectral and spatial resolution and are suitable for use in
compact hard X-ray sensors operated without cryogenics. One of the
more appealing astrophysical applications is their use as focal
plane detectors for multilayer hard X-ray telescopes operating in
the (10 - 80) keV energy band. This paper reports experimental
results obtained from two 16x16 pixellated CZT detectors (10x10x1
mm3 and 10x10x2 mm3 single crystals) with 450x450 μm2 pixel operated at room temperature using standard commercial read-out electronics. We have investigated about energy resolution and material properties of both detectors. Both arrays gave similar results showing an energy resolution less then 5%@59.5 keV and a good material uniformity. The good energy resolution of both detectors demonstrates as the pixellated anode structure reduces (small pixel effect) the incomplete charge collection due to severe hole trapping typically presents in CZT crystals. A calibration curve, obtained using three different energies, shows a linear response of the detectors.
Stefano Del Sordo, Gaetano Agnetta, B. Biondo, Ezio Caroli, Filippo Celi, Ariano Donati, Salvatore Giarrusso, A. Mangano, R. Montanti, Francesco Russo, Filomena Schiavone, John Stephen, M. Strazzeri, Giulio Ventura, Giovanni Pareschi, L. Abbene, Francesco Fauci, Giuseppe Raso, V. Radicci, S. Tangaro, Piernicola Oliva, Simone Stumbo
Cadmium zinc telluride (CZT) pixel detectors show very good spectral and spatial resolution and are suitable for use in compact hard X-ray sensors operated without cryogenics. One of the more interesting astrophysical application is their use as focal plane detectors for multilayer hard X-ray telescopes operating in the 15 - 70 keV energy band. Here we report on results obtained using a 16 x 16 CZT pixel detector (10 x 10 x 1 mm3 single crystal) with 500 μm pixels operated at room temperature using standard commercial electronics. The results clearly show that the use of small pixels is effective in reducing one of the major drawbacks of CZT planar detectors i.e. the considerable amount of charge loss, due to hole trapping, which gives rise to a reduced energy resolution and a low energy tail in the pulse-height spectra.
The CACTuS (Compact Array of Cadmium Telluride Micro Spectrometers) instrument was constructed as a prototype detection plane for the Coded Imager and Polarimeter for High Energy Radiation (CIPHER) telescope. The instrument, flown as a 'piggy-back' experiment on a stratospheric balloon as part of the Summer 2002 trans-mediterranean flight campaign from the Milo Italian balloon base in Sicily, was constructed in order to verify the feasibility of using this kind of position sensitive detector for hard X and soft gamma ray polarimetry and imaging, with the objective of studying the instrumental background at stratospheric balloon altitudes over the 20-1000 keV energy range. Of particular interest is the spectrum and distribution of Compton scattered events that trigger two pixel (double) events, the recognition of which is essential for providing a high sensitivity to linear polarisation. It was also used to evaluate the efficiency and the reliability of an off-line numerical algorithm to be applied to the CdTe flight data for signal compensation, which uses the amplitudes obtained by readout electronics with a double shaping filter stage.
The scientific instrumentation on board the x-ray astronomy satellite SAX includes a medium energy concentrator/spectrometer (MECS), operating in the energy range 1.3 - 10 keV, which consists of three identical instruments, each composed by a grazing incidence mirror unit with focal length of 1850 mm and by a position sensitive gas scintillation proportional counter. The MECS flight instruments have been calibrated at the X-ray PANTER facility of the Max Planck Institute and the preliminary results are presented in the paper.
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