J.-L. Galvèz, M. Hernanz, L. Álvarez, B. Artigues, J.-M. Álvarez, M. Ullán, M. Lozano, G. Pellegrini, E. Cabruja, R. Martínez, M. Chmeissani, C. Puigdengoles
Stellar explosions are relevant and interesting astrophysical phenomena. Since long ago we have been working on the characterization of novae and supernovae in X and gamma-rays, with the use of space missions. We have also been involved in feasibility studies of future instruments in the energy range from several keV up to a few MeV, in collaboration with other research institutes. High sensitivities are essential to perform detailed studies of cosmic explosions and cosmic accelerators, e.g., Supernovae and Classical Novae. In order to fulfil the combined requirement of high detection efficiency with good spatial and energy resolution, an initial module prototype based on CdTe pixel detectors is being developed. The detector dimensions are 12.5mm x 12.5mm x 2mm with a pixel pitch of 1mm x 1mm. Two kinds of CdTe pixel detectors with different contacts have been tested: ohmic and Schottky. Each pixel is bump bonded to a fanout board made of Sapphire substrate and routed to the corresponding input channel of the readout VATAGP7.1 ASIC, to measure pixel position and pulse height for each incident gamma-ray photon. The study is complemented by the simulation of the CdTe module performance using the GEANT 4 and MEGALIB tools, which will help us to optimise the detector design. We will report on the spectroscopy characterisation of the CdTe detector module as well as the study of charge sharing.
The Large Observatory For X-ray Timing (LOFT) is an innovative medium-class mission selected for an assessment phase in the framework of the ESA M3 Cosmic Vision call. LOFT is intended to answer fundamental questions about the behavior of matter in theh very strong gravitational and magnetic fields around compact objects. With an effective area of ~10 m2 LOFT will be able to measure very fast variability in the X-ray fluxes and spectra. A good knowledge of the in-orbit background environment is essential to assess the scientific performance of the mission and to optimize the instrument design. The two main contributions to the background are cosmic diffuse X-rays and high energy cosmic rays; also, albedo emission from the Earth is significant. These contributions to the background for both the Large Area Detector and the Wide Field Monitor are discussed, on the basis of extrensive Geant-4 simulations of a simplified instrumental mass model.
J. Gálvez, M. Hernanz, J. Álvarez, M. La Torre, L. Álvarez, D. Karelin, M. Lozano, G. Pellegrini, M. Ullán, E. Cabruja, R. Martínez, M. Chmeissani, C. Puigdengoles
KEYWORDS: Sensors, Gamma radiation, Prototyping, Gamma ray imaging, Image sensors, Data acquisition, Spatial resolution, Monte Carlo methods, Signal detection, Energy efficiency
In the last few years we have been working on feasibility studies of future instruments in the gamma-ray range, from
several keV up to a few MeV. The innovative concept of focusing gamma-ray telescopes in this energy range, should
allow reaching unprecedented sensitivities and angular resolution, thanks to the decoupling of collecting area and
detector volume. High sensitivities are essential to perform detailed studies of cosmic explosions and cosmic
accelerators, e.g., Supernovae, Classical Novae, Supernova Remnants (SNRs), Gamma-Ray Bursts (GRBs), Pulsars,
Active Galactic Nuclei (AGN). In order to achieve the needed performance, a gamma-ray imaging detector with mm
spatial resolution and large enough efficiency is required.
In order to fulfill the combined requirement of high detection efficiency with good spatial and energy resolution, an
initial prototype of a gamma-ray imaging detector based on CdTe pixel detectors is being developed. It consists of a
stack of several layers of CdTe detectors with increasing thickness, in order to enhance the gamma-ray absorption in the
Compton regime. A CdTe module detector lies in a 11 x 11 pixel detector with a pixel pitch of 1mm attached to the
readout chip. Each pixel is bump bonded to a fan-out board made of alumina (Al2O3) substrate and routed to the
corresponding input channel of the readout ASIC to measure pixel position and pulse height for each incident gamma-ray
photon.
We will report the main features of the gamma-ray imaging detector performance such as the energy resolution for a set
of radiation sources at different operating temperatures.
DUAL will study the origin and evolution of the elements and explores new frontiers of physics: extreme energies that
drive powerful stellar explosions and accelerate particles to macroscopic energies; extreme densities that modify the laws
of physics around the most compact objects known; and extreme fields that influence matter in a way that is unknown on
Earth. The variability of these extreme objects requires continuous all-sky coverage, while detailed study demands an
improvement in sensitivity over previous technologies by at least an order of magnitude.
The DUAL payload is composed of an All-Sky Compton Imager (ASCI), and two optical modules, the Laue-Lens Optic
(LLO) and the Coded-Mask Optic (CMO). The ASCI serves dual roles simultaneously, both as an optimal focal-plane
sensor for deep observations with the optical modules and as a sensitive true all-sky telescope in its own right for all-sky
surveys and monitoring. While the optical modules are located on the main satellite, the All-Sky Compton Imager is
situated on a deployable structure at a distance of 30 m from the satellite. This configuration not only permits to maintain
the less massive payload at the focal distance, it also greatly reduces the spacecraft-induced detector background, and,
above all it provides ASCI with a continuous all-sky exposure.
KEYWORDS: Sensors, Gamma radiation, Monte Carlo methods, Space telescopes, Metals, Spectroscopy, Telescopes, Spatial resolution, Gamma ray imaging, Image resolution
Gamma-ray astrophysics in the MeV energy range plays an important role for the understanding of cosmic explosions
and acceleration mechanisms in a variety of galactic and extragalactic sources, e.g., Supernovae, Classical Novae,
Supernova Remnants (SNRs), Gamma-Ray Bursts (GRBs), Pulsars, Active Galactic Nuclei (AGN).
Through the development of focusing telescopes in the MeV energy range, it will be possible to reach unprecedented
sensitivities, compared with those of the currently operating gamma ray telescopes. In order to achieve the needed
performance, a detector with mm spatial resolution and very high peak efficiency is required. It will be also desirable
that the detector could detect polarization of the source.
Our research and development activities in Barcelona aim to study a gamma-ray imaging spectrometer in the MeV range
suited for the focal plane of a gamma-ray telescope mission, based on CdTe pixel detectors arranged in multiple layers
with increasing thicknesses, to enhance gamma-ray absorption in the Compton regime. We have developed an initial
prototype based on several CdTe module detectors, with 11x11 pixels, a pixel pitch of 1mm and a thickness of 2mm.
Each pixel is stud-bump bonded to a fanout board and routed to a readout ASIC to measure pixel position, pulse height
and rise time information for each incident gamma-ray photon.
We will report on the results of an optimization study based on simulations, to select the optimal thickness of each CdTe
detector within the module to get the best energy resolution of the spectrometer.
The mission concept MAX is a space borne crystal diffraction telescope, featuring a broad-band Laue lens optimized for the observation of compact sources in two wide energy bands of high astrophysical relevance. For the first time in this domain, gamma-rays will be focused from the large collecting area of a crystal diffraction lens onto a very small detector volume. As a consequence, the background noise is extremely low, making possible unprecedented sensitivities. The primary scientific objective of MAX is the study of type Ia supernovae by measuring intensities, shifts and shapes of their nuclear gamma-ray lines. When finally understood and calibrated, these profoundly radioactive events will be crucial in measuring the size, shape, and age of the Universe. Observing the radioactivities from a substantial sample of supernovae and novae will significantly improve our understanding of explosive nucleosynthesis. Moreover, the sensitive gamma-ray line spectroscopy performed with MAX is expected to clarify the nature of galactic microquasars (e+e- annihilation radiation from the jets), neutrons stars and pulsars, X-ray Binaries, AGN, solar flares and, last but not least, gamma-ray afterglow from gamma-burst counterparts.
CLAIRE is a balloon-borne experiment dedicated to validating the concept of a diffraction gamma-ray lens. This new concept for high energy telescopes is very promising and could significantly increase sensitivity and angular resolution in nuclear astrophysics. CLAIRE's lens consists of 556 Ge-Si crystals, focusing 170 keV gamma-ray photons onto a 3x3 matrix of HPGe detectors, each detector element being only 1.4x1.4x4 cm3. On June 14 2001, CLAIRE was launched by the French Space Agency (CNES)from its balloon base at Gap in the French Alps and was recovered near the Atlantic ocean (500 km to the west) after about 5 hours at float altitude. Pointing accuracy and gondola stabilization allowed us to select 1h12' of "good time intervals" for the data analysis. During this time, 33 diffracted photons have been detected leading to a 3σ detection of the source. Additional measurements made on a ground based 205 meters long test range are also presented. The results of this latter experiment confirm those of the stratospheric flight.
Three new compound structures of the optical fiber resonators for generating the single longitudinal mode are reported. Their characteristics are investigated.
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