The BaBar RadFET monitoring board

The monitoring board to interface the RadFET integrated radiation dosimeters to the BaBar detector control system is described. RadFET sensors are specially designed p-channel MOSFET transistors which measure lifetime integrated radiation exposure by measuring the source-drain voltage at a fixed current. As the device is irradiated, positive space charge is trapped in the oxide layer, which results in an increase in the source-drain voltage. Communication with the BaBar detector control system proceeds via a CANbus interface using a Motorola MC68HC705X32 microcontroller on the monitoring board and the BaBar standard EPICS-based tools on the BaBar side. The RadFET monitoring Board (RMB) can read up to thirty-two sensors. A manual control allows for adjustment of an offset voltage to increase the maximum readable value as the device receives more exposure, while retaining the original circuit precision. Results from monitoring during the first years of BaBar running are presented.