Development of a 2D digital Coincidence Doppler Broadening Spectrometer

A 2D digital spectrometer for coincidence measurement of Doppler broadening of positron annihilation radiation is developed and tested. The spectrometer is based on a 14-bit waveform digitizer which gives the possibility of fast and direct sampling of the preamplifier signals of the HPGe detectors and preserves the information required by the physics of Doppler broadening spectroscopy. Some features of the digital spectrometer are compared with its analog counterpart. Superior energy resolution, better peak symmetry, effective elimination of ballistic deficit and better stabilization of peak position are the advantages of the digital spectrometer. The performance of the digital spectrometer to support the CDBS experiment is tested by investigation on the electronic structure of some elements at 1st series of transition metals. The results show that the spectrometer is sensitive enough to distinguish the electronic structure of 3d metals differing a little in their valance band configuration.