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On stability of scintillation detectors
Summary
Photomultiplier tubes in scintillation detectors can drift over time, altering spectral peaks and causing significant counting errors. This instability depends on various factors and necessitates pre-use detector stability checks.
Area of Science:
- Nuclear instrumentation
- Radiation detection physics
Background:
- Scintillation detectors are crucial for gamma-ray spectroscopy.
- Photomultiplier tubes (PMTs) are key components in these detectors.
- PMT performance stability is vital for accurate measurements.
Purpose of the Study:
- To investigate the time-dependent pulse height changes in photomultiplier tubes within scintillation detectors.
- To quantify the impact of these changes on spectral peak positioning and counting rates.
- To identify factors influencing this observed drift phenomenon.
Main Methods:
- Exposing a scintillation detector with a photomultiplier tube to a gamma-emitting source.
- Applying high dynode voltage during exposure.
- Monitoring pulse height changes and spectral peak drift over time.
- Analyzing the dependence of drift on photon flux, voltage, and source energy.
Main Results:
- Observed significant "drift" of spectral peaks due to time-dependent pulse height changes in the photomultiplier tube.
- Detected counting rate errors of approximately 20% caused by spectral peak drift.
- Found that the drift is dependent on photon flux, high voltage level, and gamma source energy.
- Noted that this instability was not present in all tested detectors.
Conclusions:
- Photomultiplier tube instability can lead to substantial errors in scintillation detector measurements.
- Detector stability must be evaluated before critical applications.
- The observed drift highlights the importance of understanding PMT behavior under operational conditions.