In-situ calibration of a PMT inside a scintillation detector by means of primary scintillation detection

TL;DR

This paper presents a new in-situ calibration method for PMTs in scintillation detectors using primary scintillation, which is effective even when traditional methods are impractical, and compares it with the standard SER method.

Contribution

The study introduces an exponential fit-based calibration technique for PMTs that works in situ, offering an alternative to the SER method especially in sealed or inaccessible detectors.

Findings

Exponential fit method agrees with SER when mean photoelectrons are around 1.0.

SER method has higher precision than the exponential fit method.

Exponential fit method is useful for in situ calibration in sealed detectors.

Abstract

We have investigated the possibility of calibrating the PMTs of scintillation detectors, using the primary scintillation produced by X-rays to induce single photoelectron response of the PMT. The high-energy tail of this response, can be approximated to an exponential function, under some conditions. In these cases, it is possible to determine the average gain for each PMT biasing voltage from the inverse of the exponent of the exponential fit to the tail, which can be done even if the background and/or noise cover-up most of the distribution. We have compared our results with those obtained by the commonly used single electron response (SER) method, which uses a LED to induce a single photoelectron response of the PMT and determines the peak position of such response, relative to the pedestal peak (the electronic noise peak, which corresponds to 0 photoelectrons). The results of the exponential fit method agree with those obtained by the SER method when the average number of photoelectrons reaching the first dynode per light/scintillation pulse is around 1.0. The SER method has higher precision, while the exponential fit method has the advantage of being useful in situations where the PMT is already in situ, being difficult or even impossible to apply the SER method, e.g. in sealed scintillator/PMT devices.