Multiple detector system for rapid pixe analysis

An X-ray detection system using two Si(Li) detectors has been developed at the Davis cyclotron in order to obtain a suitably high sensitivity for each element. The smaller detector with thin Be window was used for the low energy region, 1 to 7 keV (Na to Fe K lines). Another one was used for the higher energy region, 5 to 15 keV (V to Sr K lines, Pb L lines). The energy dependence of the low Z detector was flattened with a pierced Kapton 'funny' filter, and a collimator was put in front of it to obtain an exact solid angle. The high Z detector was covered with a polyethylene sheet to cut out low energy X-rays. The angle between the sample plane and the detector surface was 45 degrees for each detector. The signals from both detectors were routed and accumulated in a single pulse height analyzer. A computer program has been developed to control the beam shutter, the sample exchanger and the data aquisition system, and to analyse two spectra within a minute. It is possible with this system to complete the whole analyses of 120 samples mounted in the sample changer in only two hours. The detection limit for each element in a rapid run was markedly improved, e.g., 1 ng/cm2 for Fe. The calibration run with 30 standard samples was carried out at the begining of each analysis session. The sensitivities measured with different standard sources agreed within 20 % of each other and with the calculated values using currently available data. Scattered protons were also measured with a silicon surface barrier detector concurrently with the PIXE run to obtain hydrogen concentrations. Furthermore, forward alpha scattering technique was applied on the same samples using two surface barrier detectors and the same electronics to analyze light elements H to F. Complete elemental analysis of the same sample gives us accurate matrix correction factors. (author)