ON-GROUND PERFORMANCE TESTS OF THE SAX PDS DETECTOR/

The Phoswich Detection System (PDS) is one of the four narrow field ex periments on board the SAX satellite. The PDS will be dedicated to dee p temporal and spectral studies of celestial X-ray sources in the 15-3 00 keV energy band. It also includes a gamma-ray burst monitor The PDS detector is composed of 4 actively shielded NaI(Tl)/CsI(Na) phoswich scintillators with a total geometric area of 795 cm(2) and a field of view of 1.4 degrees (FWHM). The performance of the detector before its integration with its flight electronic, was tested using standard ins trumentation. Here we present results of these tests. The measured ene rgy resolution of the phoswich units is better than 15% at 60 keV conf irming the expectations. Also test results of the anticoincidence shie ld of CsI(Na) and collimator are discussed.