Study of radiation damage in front-end electronics components

To search for a new physics and to pin down its interaction model, we start the Belle II experiment in 2015 and will continue the data taking for more than ten years. In the Belle II experiment, sub-detector hit signals are digitized by front-end electronics cards located inside or nearby the detector and the digitized signals are transmitted to receiver cards, which are located ~ 10 m away from the detector, over optical fiber links. Because of this design, radiation effects to the front-end electronics components will be a severe issue, where the annual neutron flux and γ-ray dose to them are expected to be ~ 10¹¹/cm² and ~ 80 Gy, respectively, in the worst case. We have been carrying out radiation-effect studies by those particles to the front-end electronics components using experimental exposure facilities. In the series of previous studies, we found optical transceivers that we studied were very sensitive to γ rays and had only four-year-equivalent radiation hardness in the Belle II operation. To solve this problem, we search for an optical transceiver with sufficient radiation hardness for Belle II by bombarding several commercial optical transceivers with γ rays. We isolate the AFBR-57D7APZ transceiver (AVAGO) as the one with the highest radiation hardness among the tested products. We quantify the AFBR-57D7APZ transceiver operates until receiving >; 900 Gy total γ-ray dose, which is a sufficient radiation hardness for the Belle II use.