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Дата последнего поиска статьи во внешних источниках: 10 ноября 2014 г.
Аннотация:The LHCb Vertex Locator (VELO) is a silicon strip detector designed toreconstruct charged particle trajectories and vertices produced at the LHCbinteraction region. During the first two years of data collection, the 84 VELOsensors have been exposed to a range of fluences up to a maximum value ofapproximately 45 × 1012 1 MeV neutron equivalent(1 MeV neq). At the operational sensor temperature of approximately−7 °C, the average rate of sensor current increase is18 μA per fb−1, in excellent agreement withpredictions. The silicon effective bandgap has been determined using currentversus temperature scan data after irradiation, with an average value ofEg = 1.16±0.03±0.04 eV obtained. The first observation ofn+-on-n sensor type inversion at the LHC has been made, occurring at a fluenceof around 15 × 1012 of 1 MeV neq. The only n+-on-psensors in use at the LHC have also been studied. With an initial fluence ofapproximately 3 × 1012 1 MeV neq, a decrease in theEffective Depletion Voltage (EDV) of around 25 V is observed. Following this initialdecrease, the EDV increases at a comparable rate to the typeinverted n+-on-n type sensors, with rates of (1.43±0.16) × 10−12 V/ 1 MeV neq and (1.35±0.25) × 10−12 V/ 1 MeV neq measured for n+-on-p andn+-on-n type sensors, respectively. A reduction in the charge collectionefficiency due to an unexpected effect involving the second metal layer readoutlines is observed.