UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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2024-11-23 18:13
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Conference: Bucharest University Faculty of Physics 2019 Meeting


Section: Nuclear and Elementary Particles Physics


Title:
Positron annihilation lifetime spectroscopy


Authors:
Marin FOCSANEANU


*
Affiliation:


E-mail
focsaneanumarin@gmail.com


Keywords:
digital, spectroscopy, positron


Abstract:
Positron annihilation lifetime spectroscopy (PALS) provides a very powerful technique for non-destructive microstructure investigations in a broad field of material classes such as metals, semiconductors, polymers or porous glasses. Even though this method is well established for more than five decades, no proper standardization for the used setup configuration and subsequent data processing exists. Eventually, this could lead to an insufficiency of data reproducibility and avoidable deviations. Based on V1742 CAEN fast digitizer, a digital positron lifetime spectrometer has been developed and tested in this work. It includes two ORTEC BaF2 scintillation detectors , a CAEN VME controller and a CAEN VME rack together with a computer. The design includes a custom written C/C++ software application to interface with the hardware and process the data efficiently. Tests reveal a 240 ps time resolution and a 220 ps positron lifetime in silicon, comparable with conventional analog lifetime spectrometers using the same type of detector. To measure the time resolution, a 60Co radioactive source was used. The analog section consists of nuclear instrument modules (NIM). The pulse processing part of the spectrometer is able to analyze and store in real-time several thousands of events per second, which is an order of magnitude more than the count rates in typical positron lifetime experiments. These improvements makes this digital spectrometer more simple and convenient in comparison with other spectrometers, and it can be applied to the other scintillation timing measurements with picosecond accuracy. In particular, with this spectrometer we are planning to study polymers.