A Model for the Secondary Scintillation Pulse Shape from a Gas Proportional Scintillation Counter

TL;DR

This paper develops an analytic and Monte Carlo model for the secondary scintillation pulse shape in gas proportional scintillation counters, aiding detector design, systematic studies, and simulation accuracy.

Contribution

It introduces a comprehensive physics-based model incorporating event topology, geometry, and optical properties, enhancing understanding and simulation of S2 signals in PSCs.

Findings

Model matches experimental data from argon GPSC

Analytic form enables general detector studies

Monte Carlo model allows detailed event simulation

Abstract

Proportional scintillation counters (PSCs), both single- and dual-phase, can measure the scintillation (S1) and ionization (S2) channels from particle interactions within the detector volume. The signal obtained from these detectors depends first on the physics of the medium (the initial scintillation and ionization), and second how the physics of the detector manipulates the resulting photons and liberated electrons. In this paper we develop a model of the detector physics that incorporates event topology, detector geometry, electric field configuration, purity, optical properties of components, and wavelength shifters. We present an analytic form of the model, which allows for general study of detector design and operation, and a Monte Carlo model which enables a more detailed exploration of S2 events. This model may be used to study systematic effects in currents detectors such as energy and position reconstruction, pulse shape discrimination, event topology, dead time calculations, purity, and electric field uniformity. We present a comparison of this model with experimental data collected with an argon gas proportional scintillation counter (GPSC), operated at 20 C and 1 bar, and irradiated with an internal, collimated 55Fe source. Additionally we discuss how the model may be incorporated in Monte Carlo simulations of both GPSCs and dual-phase detectors, increasing the reliability of the simulation results and allowing for tests of the experimental data analysis algorithms.