G. Agnetta

Characterization of a CZT focal plane small prototype for hard X-ray telescope

The promise of good energy and spatial resolution coupled with high efficiency and room temperature operation has fuelled a large international effort to develop cadmium zinc telluride (CZT) for hard X-ray applications. We are involved on the development of a hard X-ray telescope based on multilayer optics and focal plane detector operative in the 10-80 keV energy range. This telescope requires a high efficiency focal plane providing both fine spatial resolution and spectroscopy with a compact and robust design. This paper reports preliminary results on the characterization both in spectroscopic and spatial response of two small pixellated CZT detectors (10times10times1 mm3 and 10times10times2 mm3 single crystals) with 0.45 mm pixel size. We present the results obtained using both standard commercial read-out electronics Readout Electronics for Nuclear Applications (RENA) and innovative low noise and low power dissipation ASICs developed within the collaboration

The atmospheric nightglow in the 300–400 nm wavelength: Results by the balloon-borne experiment “BABY”

Abstract The balloon-borne experiment, named BAckground BYpass (BABY) belongs to a wider program that has as its final goal the detection and study of high-energy cosmic rays from space (satellite, Space Station). An information of fundamental importance for this class of projects concerns the nighttime background light. The instrument designed to detect fluorescence photons is basically composed of two collimated photomultipliers: a single photon-counting PMT and a charge integration PMT. We briefly report the details of the design, operation and performance of the detector, which was designed and completely built at the IFCAI–CNR Institute in Palermo. Preliminary analysis and results of the nocturnal background in the range of 300– 400 nm are presented for the whole duration of the flight during the 1998 Mediterranean balloon flight campaign. A substantial part of the flight was at night over the sea.

UVSiPM: A light detector instrument based on a SiPM sensor working in single photon counting

Abstract UVSiPM is a light detector designed to measure the intensity of electromagnetic radiation in the 320–900 nm wavelength range. It has been developed in the framework of the ASTRI project whose main goal is the design and construction of an end-to-end Small Size class Telescope prototype for the Cherenkov Telescope Array. The UVSiPM instrument is composed by a multipixel Silicon Photo-Multiplier detector unit coupled to an electronic chain working in single photon counting mode with 10 nanosecond double pulse resolution, and by a disk emulator interface card for computer connection. The detector unit of UVSiPM is of the same kind as the ones forming the camera at the focal plane of the ASTRI prototype. Eventually, the UVSiPM instrument can be equipped with a collimator to regulate its angular aperture. UVSiPM, with its peculiar characteristics, will permit to perform several measurements both in lab and on field, allowing the absolute calibration of the ASTRI prototype.

Performances of RPC detectors with tracking & timing electronics

Abstract The bakelite Resistive Plate Counters (RPC) for the COVER_PLASTEX experiment have been tested with special tracking & timing electronics developed by the T&T collaboration for use as a front-end electronics able to give position and arrival time for each particle in the EAS front crossing the detector. Results on single counting rate, efficiency, time resolution, signal shape and afterpulse presence are given as a function of the high voltage and input signal threshold.

Measurements of spectral and position resolution on a 16x16 pixel CZT imaging hard x-ray detector

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.

Characterisation of a CZT focal plane small prototype for hard X-ray telescope

We are working on the development of a balloon borne telescope based on multilayer optics for energy from /spl sim/10 keV up 80 keV. This hard X-ray telescope requires a high efficiency focal plane providing both fine spatial resolution and spectroscopy with a compact and robust design. Currently the most appealing choice is offered by the development of CdTe/CZT detectors. Herein we present the characterization both in spectroscopic and spatial response of a small CZT detector (1 cm/sup 2/) with 0.5 mm pixel size. The readout of the detector use an innovative low noise and low power dissipation ASICs developed within the collaboration. We present the results of tests with both collimated and non collimated radioactive sources using the RENA front-end electronics and a back-end electronics, that comprises a 64 independent channels system with coincidence logic.

T&T: a new design for a front-end time digitizer electronics

Abstract A front-end readout electronics of new design is described. This electronics can operate in cosmic ray and extended air showers (EAS) as well as in accelerator experiments. The T&T (tracking and timing) electronics has been planned to cover large area detectors avoiding the necessity of tedious and time consuming cable calibrations. It is characterized by a 2 ns time resolution, multihits recording capability, no ambiguity in event-pulse reconstruction, daisy-chain interconnection, low power consumption and low cost.

Evaluation of the optical cross talk level in the SiPMs adopted in ASTRI SST-2M Cherenkov Camera using EASIROC front-end electronics

ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana), is a flagship project of the Italian Ministry of Education, University and Research whose main goal is the design and construction of an end-to-end prototype of the Small Size of Telescopes of the Cherenkov Telescope Array. The prototype, named ASTRI SST-2M, will adopt a wide field dual mirror optical system in a Schwarzschild-Couder configuration to explore the VHE range of the electromagnetic spectrum. The camera at the focal plane is based on Silicon Photo-Multipliers detectors which is an innovative solution for the detection astronomical Cherenkov light. This contribution reports some preliminary results on the evaluation of the optical cross talk level among the SiPM pixels foreseen for the ASTRI SST-2M camera.

Investigation on pixellated CZT detectors coupled with a low power readout ASIC

In this work, we investigated on the spectroscopic performances of two pixellated CZT detectors coupled with a custom low noise and low power readout ASIC. The detectors (10 x 10 x 1 mm3 and 10 x 10 x 2 mm3 single crystals) consist of an array of 256 pixels with a geometric pitch of 0.5 mm. The ASIC, fabricated in 0.8 μm BiCMOS technology, is equipped with eight independent channels (preamplifier and shaper) characterized by a dynamic range from 10 keV to 100 keV, low power consumption (0.5 mW/channel) and low noise (150–500 electrons r.m.s.). The spectroscopic results point out the good energy resolution of both detectors at room temperature (5.8 % FWHM at 59.5 keV for the 1 mm thick detector; 5.5 % FWHM at 59.5 keV for the 2 mm thick detector) and low tailing, confirming the single charge carrier sensing properties of the CZT detectors equipped with a pixellated anode layout. Temperature measurements show optimum performances of the system (detector and electronics) at T = 10 °C and performance degradations at lower temperatures. The detectors and the ASIC, designed by our collaboration, represent two small focal plane detector prototypes for hard X-ray telescopes operating in the 10–100 keV energy range.

Figaro II experiment: description and technical performance

Abstract The FIGARO II (French Italian GAmma Ray Observatory) experiment designed to observe cosmic sources with a well established time signature is described. It consists of a large-area (3600 cm 2 ) array of nine tiles of NaI(Tl), actively shielded against the environmental background, to be operated at high altitude by means of a stratospheric balloon for the detection of celestial gamma rays in the energy band 0.17–6.0 MeV. The performance of this experiment derived from calibrations with radioactive sources and flight data is presented. The actual sensitivity allows the detection of a pulsed signal with a flux of 5×10 −5 ph/(cm 2 s MeV) (≈ 6% of the Crab pulsar flux), in the whole energy band at 3 standard deviations in an observation time of 6 hours.