Abstract
Combining strong signal amplification made possible by Gaseous Electron Multipliers (GEMs) with the high spatial resolution provided by optical readout, highly performing radiation detectors can be realized. An optically read out GEM-based Time Projection Chamber (TPC) is presented. The device permits 3D track reconstruction by combining the 2D projections obtained with a CCD camera with timing information from a photomultiplier tube. Owing to the intuitive 2D representation of the tracks in the images and to automated control, data acquisition and event reconstruction algorithms, the optically read out TPC permits live display of reconstructed tracks in three dimensions. An Ar/CF4 (80/20%) gas mixture was used to maximize scintillation yield in the visible wavelength region matching the quantum efficiency of the camera. The device is integrated in a UHV-grade vessel allowing for precise control of the gas composition and purity. Long term studies in sealed mode operation revealed a minor decrease in the scintillation light intensity.
Highlights
The universality of Time Projection Chambers (TPCs) [1] makes them an attractive detector concept for a wide range of applications
We present a TPC based on a triple-Gaseous Electron Multipliers (GEMs) amplification stage optically read out by a high-resolution CCD camera, which provides an image of the 2D projection of alpha tracks, and a Photomultiplier Tubes (PMTs), which simultaneously provides timing information to perform 3D track reconstruction
An optically read out GEM-based detector was operated as a TPC to demonstrate the live event reconstruction capabilities of the presented device for alpha particles
Summary
The universality of Time Projection Chambers (TPCs) [1] makes them an attractive detector concept for a wide range of applications. To permit an accurate 3D reconstruction of particle tracks, the 2D projection on the endcap of a TPC must be recorded with possibly high spatial resolution. To enable the detection of various types of radiation from lowenergy X-rays to highly ionizing alpha particles, robust signal amplification technologies such as Gaseous Electron Multipliers (GEMs) can be employed [2]. This variety of MicroPattern Gaseous Detectors (MPGDs) is composed of thin perforated foils with a conductor– insulator–conductor structure and allows for high electron multiplication factors by avalanche amplification in high electric field regions in the GEM holes with typical diameters of tens of micrometers. In view of directional dark matter search experiments, optically read out GEM-based TPCs have been suggested and investigated as a candidate technology for providing accurate information about electron and nuclear recoil tracks [7]
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