The low-energy concentrator spectrometer on-board the BeppoSAX X-ray astronomy satellite

The payload of the Italian/Dutch spacecraft BeppoSAX includes a set of four X-ray concentrators each of geometric area 124 cm(2) together with imaging gas scintillation proportional counter detectors located at the focal planes. One of these detectors, the Low-Energy Concentrator Spectrometer (LEGS), is sensitive to X-rays in the energy range 0.1 - 10 keV, while the other three cover a narrower energy range of 1.3 - 10 keV. In order to achieve the extended low-energy response of the LEGS a novel type of gas scintillation proportional counter has been developed which dispenses with the separate drift and scintillation regions of conventional instruments. The design and performance of the instrument together with its calibration and data analysis system are described here.