Performance of Si sensors irradiated to <f>5×1014 n/cm2</f>

The expected particle fluence in the inner part of the CMS Preshower is calculated to be <f>1.6×1014 cm-2</f> for neutrons and <f>0.4×1014 cm-2</f> 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 <f>5×1014 n/cm2</f> to verify that they hold voltages necessary to reach the full charge collection efficiency. All irradiated sensors showed no signs of breakdown up to <f>1000 V</f>, the maximum voltage applied. All but one display a sufficiently stable charge collection efficiency up to <f>1000 V</f>. No noisy channels were observed at the extreme voltages.The measured charge collection efficiency was <f>71±12%</f> and <f>59±12%</f> for sensors irradiated to <f>3×1014</f> and <f>5×1014 n/cm2</f>, respectively. These values are consistent with the extrapolation from previous measurements made on sensors irradiated to <f>2.3×1014 n/cm2</f>.The work presents the results of static and dynamic measurements and shows that our design and the technology are very robust. [Copyright &y& Elsevier]