Study on the Aging of the BGO Calorimeter of the DAMPE Experiment in Space

The dark matter particle explorer (DAMPE) has been in operation stably for nearly seven years. The key sub-detector of DAMPE is the bismuth germanium oxide (BGO) electromagnetic (EM) calorimeter, which consists of 308 BGO crystal bars. As a long-term apparatus in space, the BGO calorimeter faces continuous radiation bombardment, and therefore, the radiation resistance of the BGO is crucial for the performance of energy measurement. To understand the aging of BGO crystals caused by radiation in space, the stability including attenuation length and absolute energy scale has been examined with on-orbit data over 6.5 years. The aging effects are found in the BGO crystals of the inner and outer parts of the BGO calorimeter. Due to real-time calibration, the BGO calorimeter is still in a stable operation status.