6533b862fe1ef96bd12c6b44

RESEARCH PRODUCT

Test Measurements of Modernized Version of Two-Detector Doppler Spectrometer

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The quality of the annihilation quanta energy measurements (Doppler effect) has greatly increased when experimenters have begun to introduce Doppler apparatus modifications. In the basic version, the experimental set-up consisted of high energy resolution Ge(Li) detector, amplifier and multichannel analyser. A simple construction and short time of data acquisition were the main advantages of that version of the apparatus. Competitive, angular correlation of annihilation radiation (ACAR) method was better from the resolution point of view and not worse when considering the range of momentum distribution, but the ACAR method required high activity positron sources and data acquisition time was at least one order of magnitude longer than in Doppler measurements. The first important modification of Doppler apparatus was connected with an increase in the measured momentum distribution range. It was possible by introducing a coincidence mode, where the second detector was used as the register of the second annihilation photon. The coincidence system considerably eliminated pile-up events, cosmic rays or, as in the case of using Na 22 source, the Compton scattered nuclear photons (1.28 MeV). It caused that the high momentum range of . spectra, which had never been seen earlier, could be investigated [1-3]. The annihilation lines, measured in that convention, were asymmetrical due to the incomplete charge collection and it turned out to be a bit confusing because of the