Progress with the gas electron multiplier

The Gas Electron Multiplier (GEM) amplifies electrons released in a gas and transfers them to a second element of detection, multiwire or microstrip chamber. We describe recent developments realized with two GEM meshes in series, followed by a simple printed circuit as read-out electrode. Full detection efficiency for minimum ionizing electrons has been obtained, with good energy and time resolution; bi-dimensional localization can be achieved recording the induced signals on orthogonal strips printed on a double-sided thin circuit. While with a single, 50-μm thick GEM mesh amplification factors around one hundred are attained, with a twin mesh having the facing electrodes in electrical contact (emulating a thicker GEM) we have obtained gains in excess of a thousand, large enough for efficient detection of radiation. We believe that this can lead to the development of a new generation of simple, reliable, cheap detectors for high-rate tracking and bi-dimensional imaging of radiation.