A compact and finely grained sandwich calorimeter is designed to instrument the very forward region of a detector at a future e + e − collider. The calorimeter will be exposed to low energy e + e − pairs originating from beamstrahlung, resulting in absorbed doses of about one MGy per year. GaAs pad sensors interleaved with tungsten absorber plates are considered as an option for this calorimeter. Several Cr-doped GaAs sensor prototypes were produced and irradiated with 8.5-10 MeV electrons up to a dose of 1.5 MGy. The sensor performance was measured as a function of the absorbed dose.
The microstructure and properties of thin (~100 nm) SnO 2 films with noble metals Pt, Pd, Au additives, grown by dc magnetron deposition are studied. It is shown that the introduction of additives into the bulk and the deposition of dispersed catalysts on the semiconductor surface make it possible to control the sensor parameters in pure air and upon exposure to reduction (CO, H 2 , CH 4 ) and oxidation (NO 2 ) gases. Possible mechanisms for the effect of Pt, Pd, Au on the bulk and surface properties of tin dioxide are dis cussed. The technological conditions for film growth, which provide the selective detection of low concen trations (10-100 ppm) of CO and H 2 , below explosive concentrations (0.5-2.5 vol %) of methane, and trace concentrations (0.05-5 ppm) of NO 2 are determined.
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