Performance of Si sensors irradiated to 5x1014 n/cm2

The expected particle fluence in the inner part of the CMS Preshower is calculated to be 1.6x1014 cm-2 for neutrons and 0.4x1014 cm-2 for charged hadrons. Since the error of the calculation is high and/or unexpected accidental beam misalignments might happen we have irradiated Preshower silicon sensors to fluences up to 5x1014 n/cm2 to verify that they hold voltages necessary to reach the full charge collection efficiency. All irradiated sensors showed no signs of breakdown up to 1000 V, the maximum voltage applied. All but one display a sufficiently stable charge collection efficiency up to 1000 V. No noisy channels were observed at the extreme voltages. The measured charge collection efficiency was 71±12% and 59±12% for sensors irradiated to 3x1014 and 5x1014 n/cm2, respectively. These values are consistent with the extrapolation from previous measurements made on sensors irradiated to 2.3x1014 n/cm2. The work presents the results of static and dynamic measurements and shows that our design and the technology are very robust