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- This workshop was organized with the help
of:
- This workshop was organized with the help
of:
LIST of ABSTRACTS
| Scientific requirements and
prospects |
Gamma-ray Optics |
| Focal plane
instrumentation |
Ground facilities and
Flight systems |
Budtz-Jorgensen Carl
CZT detector development at DNSC
At the Danish National Space Center we have during the past decade been engaged in a development program on compound semiconductor detectors for hard X- and gamma rays. The most promising detector materials are based on CdTe and CdZnTe compounds which offer room temperature operation, energy ranges from a few keV up into the MeV range, excellent timing properties and sub mm position resolutions.
At DNSC we utilized the drift detector principle to minimize and correct for the less efficient charge collection properties of these compounds compared e.g. to those of Ge. We have demonstrated that CdZnTe drift detectors can achieve energy resolutions (e.g. 3.8 keV FWHM @ 661 keV) which approach those of Ge detectors.
The CdZnTe drift detector has further the advantage that it is depth sensitive which means that pixelated drift detectors become 3D devices. This property can be used for background rejection purposes and offer the possibility to construct very compact CdZnTe Compton cameras.
The DNSC detector programme will be presented with emphasis on applications for focal plane instrumentation for high energy focussing optics..Ernst-Jan Buis
New scintillators for focal plane detectors in gamma-ray missions
Recent developments of cerium doped Lanthanum halide scintillators like LaBr$_3$:Ce show a remarkable performance in gamma-ray spectroscopy.
When high energy resolution in combination with stopping power is required they provide excellent gamma-ray detector candidates for the use in space missions. Moreover, irradiation tests have shown that such detectors, in contrast to commonly used spectrometers like germanium, are radiation tolerant.
In this paper we show results on recent proton irradiation test at KVI in Groningen (NL) and discuss the damage and activation effects after irradiation. We have studied the possible applications of LaBr in nuclear astrophysics missions.
We therefore have simulated the expected signal on the focal plane and convolved it with the measured instrument response. Finally we discuss a possible design for such a focal plane detector.Caroli Ezio
Polarisation measurements with CdTe pixel array detector for Laue hard X-ray focusing telescopes
Polarimetry is an area of high energy astrophysics which is still relatively unexplored, even though it is recognized that this type of measurement could drastically increase our knowledge of the physics and geometry of high energy sources. For this reason, in the context of the design of a Gamma-Ray Imager based on new hard-X and soft gamma ray focusing optics for the next ESA Cosmic Vision call for proposals (Cosmic Vision 2015-2025), it is important that this capability should be implemented in the principal on-board instrumentation. For the particular case of the wide bandpass Laue optics we propose a focal plane based on a thick pixelated CdTe matrix detector operating with high efficiency between 60-600 keV. The high segmentation of this type of detector (0.5-1 mm pixel size) and the good energy resolution (a few keV at 500 keV) will allow high sensitivity polarisation measurements (a few % for a 10 mCrab source in 105s) to be performed. We have evaluated the modulation Q factors and minimum detectable polarisation through the use of Monte Carlo simulations (based on the GEANT 4 toolkit) for on-axis sources with power low emission spectra using the analytical response parameters of the Laue lens. An evaluation of possible background reduction using Compton kinematics will also be presented.
Caroli Ezio
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 £1 mm, an energy resolution of 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 both operate as a separate position sensitive detector and polarimeter or work with other layers to increase the overall full energy 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.
Quadrini Egidio
Solid state CZT detectors for Gamma Ray Telescope Application
The success of the IBIS Imager detector arrays on board the ESA Gamma-ray mission INTEGRAL has encouraged the high energy community to continue a robust R&D program. This activity is a mandatory work to be ready for the next Announcement of Opportunity to propose a new generation Space-born Gamma Ray focusing instrument. Such an instrument, in view of the high energy focusing feature and large sensitive area will be naturally designed with room temperature CZT/CdTe detectors. The Scientific Requirement foresee an energy range in the ~5-600 keV span, good sensitivity (1mCrab in a day observation), energy resolution of ~ 1% at 100keV and unprecedented spatial (arcmin to arcsec) and timing resolution. CZT detectors have good linearity versus temperature or bias, can be arranged in compact matrix and operate well at room temperature. The desired performances can be achieved trough a great care in the crystal production and with the help of an enhanced readout system. This is based on a flash ADC coupled to a signal form elaboration unit. The use of powerful FPGA devices will allow to get round the amplitude uncertainty due to the photon interaction deep, to remove unwanted signals (adronic tracks, random coincidences) and to permit multiple events reconstructions and signal polarisation analysis. Finally, due to the possibility to select the pixel dimension in a wide range, e.g. from <0.1 mm up to > 1 cm, this detector has the flexibility to be profitably used in large area arrays, up to several squared meter, as well as in the focal plane of high energy optics.
Takahashi Tadayuki
High Sensitivity Si/CdTe Compton Telescope
In the soft gamma-ray band up to 1 MeV, a narrow field-of-view Compton gamma-ray telescope utilizing several tens of layers of thin Si or CdTe detector will provide precise spectra with much higher sensitivity than present instruments. Based on our recent achievements of high resolution Si strip detectors and CdTe pixel detectors, we have succeeded to demonstrate Si/CdTe Compton camera. In addition to the imaging and spectroscopic observation, we have succeeded to measure polarization by using phi distribution of scattered photon. Here we will present the concepts of a narrow-FOV Compton telescope based on the results from our prototype. A proposal of a focal plane detector for a gamma-ray lens will also be presented.
Weidenspointer Georg
Monte Carlo Study of Detector Concepts for the MAX Laue Lens Gamma-Ray Telescope
MAX is a proposed gamma-ray telescope consisting of a Laue lens that focuses incident photons onto a distant detector. The lens and the detector are carried by two separate satellites flying in formation. Significant effort is being devoted to studying different types of crystals that may be suitable for focusing gamma rays in two energy bands centered on two lines which constitute the prime astrophysical interest of the MAX mission: the 511 keV positron annihilation line, and the 847 keV line from the decay of 56Co copiously produced in Type Ia supernovae. However, to optimize the performance of MAX, it is also necessary to optimize the detector used to collect the source photons concentrated by the lens. We address this need by applying proven Monte Carlo and event reconstruction packages to predict the performance of MAX for three different Ge detector concepts: a standard co-axial detector, a segemented Ge detector, and a Compton camera consisting of a stack of strip detectors. Each of these exhibits distinct advantages and disadvantages regarding fundamental performance characteristics such as detection efficiency or background rejection, which ultimately determine achievable sensitivities.
Wunderer Cornelia
Simulated Performance of dedicated Ge Strip Compton Telescopes as gamma-Lens Focal Plane Instrumentation
With focusing of gamma-rays in the nuclear-line energy regime starting to establish itself as a feasible and very promising approach for high- sensitivity gamma-ray (line) studies of individual sources, optimizing the focal plane instrumentation for gamma-ray lens telescopes is a prime concern.
Germanium detectors offer the best energy resolution available at ~2 keV FWHM and thus constitute the detector of choice for a spectroscopy mission in the MeV energy range. Using a Compton detector focal plane has three advantages over monolithic detectors: additional knowledge about (Compton) events enhances background rejection capabilities, the inherently finely pixellated detector naturally allows the selection of events according to the focal spot size and position, and Compton detectors are inherently sensitive to gamma-ray polarization.
We will use the extensive simulation and analysis package used for the ACT Vision mission study to explore achievable sensitivities for different Ge Compton focal plane configurations as a first step towards determining an optimum configuration..
Update : September 2005
Questions and comments : Peter von Ballmoos