The coordinate sensitive detector with high space and time resolution based on the MA-20 multianode PMT

Abstract

The work is dedicated to the discussion of the possibility of creating a position-sensitive detector with high coordinate reconstruction. The paper presents the simulation results and the experimentally obtained data for a prototype detector based on the MA-20 multianode PMT [1] and a linear stack of scintillating crystal or plastic strips. The multianode position-sensitive PMT MA-20 has a semitransparent bi-alkaline photocathode with the size of the sensitive area of 10 × 200 mm2, 10 evaporated type bi-alkaline type dynodes of the same length, and 20 separated anodes. This PM is the invention of the authors. The maximum gain of the dynode system is 106. The stack of scintillating strips made of GSO (gadolinium orthosilicate) crystals with an element size of 3 × 10 × 50 mm3, of BGO (bismuth germanate) crystals with an element size of 5 × 15 × 40 mm3, and finally stack of strips made of a plastic scintillator with an element size of 5 × 10 × 200 mm3 were used for experimental measurement of a spatial resolution of the detector prototype. Space resolution was determined by the position of the center of gravity of charges of neighboring anodes [2]. As a source of radiation, the collimated 137Cs (γ 0.662 MeV) and 90Sr (β− 2.283 MeV) were used, the measured number of photoelectrons is 10–20 of one element of the stack, depending on the scintillating strip type. The use of a multi-anode photomultiplier in combination with the stack of crystal or plastic scintillators allows one to get a simple linear detector with high performance in spatial resolution and also with a low level of intrinsic noise in comparison, for example, with silicon PMT. A resolution simulation was performed for a system consisting of a one-dimensional stack of scintillation strips placed on the photocathode of a multi-anode PMT for different values of the strips width and the number of photoelectrons of one strip. The experimental dependences of the signal value versus position of optical fiber with a diameter of 1 mm on the photocathode of the 20 anodes PMT were also measured that allowed to specify the coordinate resolution for the described detector. As a result of processing the collected data, spatial resolution was obtained at the level of 1 mm. The obtained results are in good agreement with the simulation results.