e-ASTROGAM is a gamma-ray space mission to be proposed as the M5 Medium-size mission of the European Space Agency. It is dedicated to the observation of the Universe with unprecedented sensitivity in the energy range 0.2 { 100 MeV, extending up to GeV energies, together with a groundbreaking polarization capability. It is designed to substantially improve the COMPTEL and Fermi sensitivities in the MeV-GeV energy range and to open new windows of opportunity for astrophysical and fundamental physics space research. e-ASTROGAM will operate as an open astronomical observatory, with a core science focused on (1) the activity from extreme particle accelerators, including gamma-ray bursts and active galactic nuclei and the link of jet astrophysics to the new astronomy of gravitational waves, neutrinos, ultra-high energy cosmic rays, (2) the high-energy mysteries of the Galactic center and inner Galaxy, including the activity of the supermassive black hole, the Fermi Bubbles, the origin of the Galactic positrons, and the search for dark matter signatures in a new energy window; (3) nucleosynthesis and chemical evolution, including the life cycle of elements produced by supernovae in the Milky Way and the Local Group of galaxies. e-ASTROGAM will be ideal for the study of high-energy sources in general, including pulsars and pulsar wind nebulae, accreting neutron stars and black holes, novae, supernova remnants, and magnetars. And it will also provide important contributions to solar and terrestrial physics. The e-ASTROGAM telescope is optimized for the simultaneous detection of Compton and pair-producing gamma-ray events over a large spectral band. It is based on a very high technology readiness level for all subsystems and includes many innovative features for the detectors and associated electronics.
KEYWORDS: Monte Carlo methods, Point spread functions, Dispersion, Calibration, Matrices, Space telescopes, Telescopes, Sensors, Photon transport, Particles
AGILE is a γ/X-ray telescope which has been in orbit since 23 April 2007. The
γ-ray detector, AGILE-GRID,
has observed Galactic and extragalactic sources, many of which were collected in the first AGILE Catalog.
We present the calibration of the AGILE-GRID using in-flight data and updated Monte Carlo simulations,
producing response matrices for the effective area, energy dispersion, and point spread dispersion as a function
of pointing direction in instrument coordinates and energy.
We performed Monte Carlo simulations in GEANT3 at different
γ-ray photon energies and incident angles,
using Kalman filter-based photon reconstruction and on-board and on-ground filters. Long integrations of in-flight observations of the Vela, Crab and Geminga sources in broad and narrow energy bands were used to validate
During the last decades, low temperature detectors have undergone a considerable growth and are now widely
acknowledged as useful instruments in many fundamental physics experiments. In this field, the phonon mediated
particle detectors known as bolometers are remarkable and are successfully used in various branches of physics
research for their good sensitivity, energy resolution and flexibility in the choice of the constituting materials.
Bolometers have proved to be powerful devices for radiation detection; in particular, they are able to detect
Gamma-rays with resolutions comparable to those obtained with the best Ge diodes. They are also suited for
applications in the area of nuclear and particle physics, like the study of rare events or dark matter. Although
an effective technique, the use of bolometers in the specific field of the search for neutrinoless double beta
decay is affected by the lack of spatial resolution. This results in the expected signal of this rare decay hidden
under an indistinguishable background due to possible surface radioactive contaminations in the materials facing
the detectors. An approach to this problem is to make bolometers surface sensitive by applying ultra-pure
crystalline foils on the main detector through direct thermal contact and by operating them as active shields.
In this contribution we present for the first time surface sensitivity achieved with large mass TeO2 bolometers
(~800 g) operated underground at ~10 mK, dedicated to the detection of neutrinoless double beta decay of
130Te. Our encouraging measurements suggest that this could be a viable method for the discrimination of
background events.
The AGILE Mission will explore the gamma-ray Universe with a very innovative instrument combining for the first time a gamma-ray imager (sensitive in the range 30 MeV - 50 GeV) and a hard X-ray imager (sensitive in the range 15-45 keV). An optimal angular resolution and a large field of view are obtained by the use of state-of-the-art Silicon detectors integrated in a very compact instrument. AGILE will be operational at the beginning of 2007 and it will provide crucial data for the study of Active Galactic Nuclei, Gamma-Ray Bursts, unidentified gamma-ray sources, Galactic compact objects, supernova remnants, TeV sources, and fundamental physics by microsecond timing.
In this contribution, we describe two innovations of the structure of large mass bolometers, proposed by the cryogenic group of the Insubria University (Como) and developed in collaboration with the Firenze group. First, up to now, low temperature calorimeters do not have any sort of spatial resolution. This means that it is not possible to reject events coming from the material that faces the detectors (holder, refrigerators shields, ...). In order to cope this problem, we developed a new kind of composite bolometers able to discriminate, by means of active ultra-pure semiconductor shields, external surface events from those coming from the absorber bulk.
A second innovation that we discuss here concerns the temperature sensors. Presently, neutron transmutation doped Ge thermistors are the most common kind of phonon sensors. Unfortunately, this kind of readout dissipates power on the detector because of the thermistor biasing and also introduces a Johnson noise term. To improve energy resolution we studied and test the application of capacitive sensors that in principle could allow us to achieve a better signal-to-noise ratio. Modeling, simulations and first encouraging measurements on surface sensitive bolometers will be discussed along with preliminary results on capacitive sensors.
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.
Milano collaboration has been developing for many years large mass bolometers for particle detection, and in particular for the study of neutrinoless double beta decay of 130Te. The active components of the detectors are large mass (340 g and 790 g) TeO2 crystals, while Neutron Transmutation Doped Ge thermistors are used as phonon sensors. These devices work at low temperatures, about 5-10 mK. The mechanical and thermal connections of the detector to the thermal bath are made with PTFE pieces that hold the crystal on copper frames. Gold wires are used as electric connections. We have developed a complete thermal model for the bolometers and "ad hoc" measurements of the thermal parameters involved were performed in the Florence cryogenic laboratory. These studies have permitted to simulate the static and dynamic behaviours of the detectors. A satisfactory agreement between simulated and the experimental response has been obtained as far as the static behaviour is concerned, while the dynamic behaviour is not yet fully understood. These preliminary results however will enable us to design new detector structures in order to improve the signal-to-noise ratio and the reproducibility. Given the good performances of these devices (excellent energy resolutions were obtained, of the order of 2 keV at 911 keV and of 5 keV at 2615 keV), this technique is particularly suitable to detectors for gamma ray spectroscopy. Encouraged by this results, the Milano-Como group has joined a large international collaboration for the realization of CUORE (Cryogenic Underground Observatory for Rare Events), seraching for Dark Matter and neutrinoless Double Beta Decay, a crucial phenomenon for neutrino physics. The Cuoricino detector, a small scale test of CUORE detector, is an array of 62 large mass bolometers like those already described, and it is now in operation in the Gran Sasso undergrand laboratory (Italy). It is the largest array of bolometric detectors ever constructed.
AGILE is an ASI gamma-ray astrophysics space Mission which will operate in the 30 MeV - 50 GeV range with imaging capabilities also in the 10 - 40 keV range. Primary scientific goals include the study of AGNs, gamma-ray bursts, Galactic sources, unidentified gamma-ray sources, diffuse Galactic and extragalactic gamma-ray emission, high-precision timing studies, and Quantum Gravity testing. The AGILE scientific instrument is based on an innovative design of three detecting systems: (1) a Silicon Tracker, (2) a Mini-Calorimeter, and (3) an ultralight coded mask system with Si-detectors (Super-AGILE). AGILE is designed to provide: (1) excellent imaging in the energy bands 30 MeV-50 GeV (5-10 arcmin for intense sources) and 10-40 keV (1-3 arcmin); (2) optimal timing capabilities, with independent readout systems and minimal deadtimes for the Silicon Tracker, Super-AGILE and Mini-Calorimeter; (3) large field of view for the gamma-ray imaging detector (~3 sr) and Super-AGILE (~1 sr). AGILE will be the only Mission entirely dedicated to source detection above 30 MeV during the period 2004-2006.
Basic operation principles of phonon-mediated low-temperature detectors of radiation are briefly reviewed. Physical properties required for the energy absorbers and for the phonon sensors of the detectors are introduced and discussed. Semiconductor thermistors, superconductive tunnel junctions and transition edge films as phonon sensors are presented and critically compared. State-of-art of single quantum detection with these devices is reported. Particular emphasis is given to the detection of X-rays and Gamma-rays. In this field, low temperature devices can provide higher efficiency and energy resolution than conventional technology. The main point is that phonon-mediated low temperature detectors are characterized by a large flexibility in the choice of the material for the active part of the device. High Z materials with the proper thermal properties can therefore be selected, providing at the same time high efficiency and high signal-to-noise ratio. The unique features of low temperature detectors allow their use in many fields, ranging from fundamental physics (neutrino properties, dark matter search, astronomy) to industrial applications (X-ray fluorescence analysis).
High-Z low-temperature calorimeters are developed by an Italian collaboration (Milano-Como-Gran Sasso Underground Laboratories) in order to search for rare nuclear events and Dark Matter massive candidates. They exhibit an excellent energy resolution, close to that of Ge-diodes, but a much higher efficiency. Different high-Z materials were initially employed . A many-years optimisation work on tellurium oxide (TeO2) lead to impressive results: devices with total masses around 750 g present FWHM energy resolutions on gamma-ray peaks ranging from 1 KeV (close to the 5 KeV energy threshold) to 2.6 KeV at 2615 KeV (208Tl gamma line). A 3.2 KeV FWHM energy resolution was obtained at 5.4 MeV (210Po alpha line), which is by far the best one ever achieved with any alpha detector. These devices, operated at about 10 mK, consist of a TeO2 single crystal thermally coupled to a 50 mg Neutron Transmutation Doped (NTD) Ge crystal working as a temperature sensor. Special care was devoted to methods for response linearization and temporal stabilisation. Devices based on the same principle and specifically optimised could find applications in several fields like gamma-ray astrophysics, nuclear physics searches, environmental monitoring and radiation metrology.
We are presenting our recent developments to measure the electron antineutrino mass by studying the 187Re (beta) - spectrum end-point with high resolution thermal detectors. We will discuss the preliminary results of an array of 8 bolometers made up of AgReO4 absorbers (2.309 mg of total mass corresponding to a total 187Re active mass of about 0.905 mg of with an expected (beta) total rate of about 1.3 Hz). Their risetime of 0.7 - 1.2 ms together with their energy resolution, ranging between 21 eV and 26 eV at 1.5 KeV, should allow to set a limit of about 10 - 12 eV after one year of real time measurements.
Angelo Alessandrello, Chiara Brofferio, David Camin, C. Cattadori, Oliviero Cremonesi, Ettore Fiorini, Andrea Giuliani, A. Maglione, Benno Margesin, Angelo Nucciotti, Maura Pavan, Gianluigi Pessina, Giorgio Pignatel, Ezio Previtali, Luigi Zanotti
We are developing Si-implanted thermistors to realize high resolution microcalorimeters. We plan to use these devices in an experiment for the determination of the neutrino mass. The measure implies the evaluation of the correct end-point energy of a beta spectrum with a calorimetric approach. Our study is devoted to outline the optimum fabrication process concerning performances and reproducibility. For such reasons we have realized Si thermistors with different concentration of dopant impurities and with different implant geometries. Tests are performed between 4.2 and 1.2 K using a pumped helium cryostat, and selected samples are characterized at very low temperatures in a dilution refrigerator. Good reproducibility of the devices is necessary for producing an array of detectors. At the same time suitable electronics are developed to optimize the detectors preamplifiers link: minimization of the parasitic capacitance is necessary to reduce the integration of signal and to maximize the speed response of the detector.
A massive thermal detector consisting of a 73 g TeO2 crystal, to be used to search for double beta decay of 130Te and to detect high energy gamma-rays, is operating at aprox. 15 mK in the Gran Sasso Underground Laboratory. The FWHM resolution achieved with this detector is 5-8 KeV, slightly dependent on energy from 100 KeV to 3 MeV, showing the competitive performances of this detector in gamma-ray spectroscopy comparable with those of conventional Ge solid state detectors. Moreover this is the first massive high-resolution gamma-ray detector of atomic number larger than 32, which implies a peak to Compton ratio comparable to that of a Ge diode of a mass larger by an order of magnitude.
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