A study on photomultiplier afterpulses in TL/OSL readers |
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| Institution: | 1. Department of Radioisotopes, Institute of Physics - Centre for Science and Education, Silesian University of Technology, ul. Konarskiego 22B, 44-100 Gliwice, Poland;2. Institute of Measurement Science, Electronics and Control - Faculty of Electrical Engineering, Silesian University of Technology, ul. Akademicka 10, 44-100 Gliwice, Poland;3. Department of Nuclear Physics and Its Applications, Institute of Physics, University of Silesia, ul. Uniwersytecka 4, 40-007 Katowice, Poland;1. Federal University of Technology – Parana, Av. Desembargador Westphalen, 637 – Bloco N – Physics Academic Department, CEP 80010-110 Curitiba, PR, Brazil;2. Institute of Nuclear Physics Polish Academy of Sciences, Radzikowskiego 152, 31-342 Krakow, Poland;1. Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Trombay, Mumbai, India;2. Technical Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai, India;1. Key Laboratory of Functional Materials and Devices for Special Environments of CAS, Xinjiang Key Laboratory of Electronic Information Materials and Devices, Xinjiang Technical Institute of Physics & Chemistry of CAS, Urumqi 830011, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Laboratory of Solid State Radiation Physics, Urumqi 830011, China |
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| Abstract: | In this work we present results of investigations of afterpulses in the photomultiplier tube (PMT) EMI 9235QA built into the Daybreak TL/OSL reader. The amplitudes of pulses and the time intervals between subsequent pulses were recorded using an ultra-fast data acquisition board and a laboratory made multichannel time/amplitude analyzer. We have recorded afterpulses following background (i.e. dark) pulses, pulses induced by single light photons and by high energy photonic radiation from a number of radioactive sources (241Am, 137Cs, 60Co, 90Sr/90Y) with different X/γ energy ranges. The measurements were performed at varying PMT temperatures. Distributions of time intervals between pulses show that there are several kinds of afterpulses, accompanying primary pulses caused by ionizing radiation, that follow with delays between 10?8–10?4 s. In comparison to pulses induced by a single photoelectron, the amplitude of afterpulses varies over a wide range from less than a single photoelectron to around 10 photoelectrons. In the investigated PMT for single light photon pulses we detected 7.5% of afterpulses and for background pulses up to 31% of afterpulses. Random series of afterpulses following primary pulses change the statistical distribution of the number of pulses recorded using a photomultiplier. If the number of primary pulses follows a Poisson distribution, then total counts number has another distribution with its variance greater than the mean, clearly showing an over-dispersion. |
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| Keywords: | Afterpulses Photomultiplier Over-dispersion |
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