Effects of damage caused by non-ionizing energy loss in Si Mini-Pad sensors for the PHENIX MPC-EX

The PHENIX MPC-EX is an W/Si pre-shower detector operating at small angles with respect to the beam in the Relativistic Heavy Ion Collider (RHIC). The Si Mini-Pad sensors are the active element of the detector. The expected hadron flux to the Si Mini-Pad sensors will generate significant non-ionizing energy loss in the sensors, which may damage the crystalline structure of the sensor’s bulk material. We investigated the nature of the hadron flux to the Si Mini-Pad sensors through a full simulation and determined its effect on the sensor’s characteristics based on a beam test. The investigation showed key issues in designing a preshower detector using silicon sensors and operating under a large neutron fluence and offered valuable information on the operation of the MPC-EX detector.