Bibcode
Reglero, V.; Ballesteros, F.; Blay, P.; Porras, E.; Sánchez, F.; Suso, J.
Referencia bibliográfica
Astrophysics and Space Science, v. 276, Issue 1, p. 239-254 (2001).
Fecha de publicación:
3
2001
Revista
Número de citas
4
Número de citas referidas
3
Descripción
Two years after launch (04.21.97), LEGRI is operating on Minisat-01 in a
LEO orbit. The LEGRI detector plane is formed by two type of gamma-ray
solid state detectors: HgI_2 and CdZnTe. Detectors are embedded in a box
containing the FEE and DFE electronics. This box provides an effective
detector passive shielding. Detector plane is multiplexed by a Coded
Aperture System located at 54 cm and a Ta Collimator with a FCFOV of
22° and 2° angular resolution. The aim of this paper is to
summarize the detector behaviour in three different time scales: before
launch, during the in-orbit check-out period (IOC), and after two years
of routine operation in space. Main results can be summarized as
follows: A large fraction of the HgI_2 detectors presented during LEGRI
IOC very high count ratios from their first switch-on (May 1997).
Therefore, they induced saturation in the on-board mass memory. After
some unsuccessful attempts to reduce the count ratios by setting up
different thresholds during LEGRI IOC, all of them were switched off
except nine detectors in column 4, with a higher degree of stability.
Oppositely, the 17 CdZnTe detectors present a remarkable stability in
both their count-ratios and spectral shapes. Details about CdZnTe ground
energy calibration, in-flight calibration (using the Crab) and detector
stability are discussed hereafter. Detector efficiency function has been
computed with the fixed flight threshold used within the calibrated
energy range (20-80 KeV). It presents a maximum at 60 KeV, and
decreasing efficiencies in the lower and upper energy range ends. Both,
non-linear threshold cutting and the drop in the detector efficiency
explain the CdZnTe computed operational efficiency response.