The gas electron multiplier (GEM)

Abstract

We describe operating priciples and results obtained with a new detector component: the Gas Electrons Multiplier (GEM). Consisting of a thin composite sheet with two metal layers separated by a thin insulator, and pierced by a regular matrix of open channels, the GEM electrode, inserted on the path of electrons in a gas detector, allows to transfer the charge with an amplification factor approaching ten. Uniform response and high rate capability are demonstrated. Coupled to another device, multiwire or micro-strip chamber, the GEM electrode permit to obtain higher gains or less critical operation; separation of the sensitive (conversion) volume and the detection volume has other advantages, as a built-in delay (useful for triggering purposes) and the possibility of applying high fields on the photocathode of ring imaging detectors to improve efficiency.Multiple GEM grids in the same gas volume allow to obtain large amplification factors in a succession of steps, leading to the realization of an effective gas-filled photomultiplier. AbstractWe describe operating principles and results obtained with a new detector element: the Gas Electrons Multiplier (GEM) [1]. Consisting of a thin composite sheet with two metal layers separated by a thin insulator, and pierced by a regular matrix of open channels, the GEM electrode, inserted on the path of electrons in a gas detector, allows to transfer the charge with an amplification factor approaching ten. Uniform response and high rate capability are demonstrated. Coupled to another device, multiwire or micro-strip chamber, the GEM electrode permits to obtain higher gains or less critical operation; separation of the sensitive (conversion) volume and the detection volume has other advantages: a built-in delay (useful for triggering purposes), and the possibility of applying high fields on the photo-cathode of ring imaging detectors to improve efficiency.Multiple GEM grids in the same gas volume allow to obtain large amplification factors in a succession of steps, leading to the realization of an effective gas-filled photomultiplier.

Cryogenic avalanche detectors based on gas electron multipliers

“…It is known that GEMs may undergo charging-up effects at high incident fluxes and high anode current densities, induced by positive ion deposition on a kapton surface [26,27,18]. The charging-up effect manifests itself in that the gain-voltage characteristic depends on the flux: the gain increase with voltage is faster for higher fluxes.…”

High rate behavior and discharge limits in micro-pattern detectors

“…In a recent work, the authors of Ref. [32] have compared the performance of a standard MSGC, alone and with the addition of a gas electron multiplier as pre-amplifying stage, under identical conditions of irradiation. The results of the simultaneous exposure to a high X-rays flux (~10 4 Hz mm -2 ) and to the internal α source are summarized in Fig.…”

“…An example of distribution of discharge voltage in absence of radiation across a micro-strip chamber is shown in Fig. 1 [31,32]. For the measurement, realized with a 10x10 cm 2 MSGC plate with thin chromium anode and cathode strips at 200 µm pitch manufactured on diamond-like coated glass [33], groups of 16 strips were sequentially activated with all others left floating; each entry in the histogram represent the discharge voltage threshold for one group.…”

Recent advances in X-ray detection with micro-hole and strip plate detector

“…Gains exceeding 10 3 are achieved with a single GEM; higher gains can be obtained by cascading several GEMs or by coupling GEMs with other gaseous electron multipliers. It was demonstrated that a micro-strip gas counter (MSGC) [2] preceded by a GEM has higher gain and stability compared to the MSGC alone [3]. Localization can be obtained in GEM detectors by coupling a properly patterned readout anode to a GEM [4].…”