To elucidate the physical mechanisms underlying the synergistic effects between the total γ dose and neutron displacement damage in bipolar process devices，in this paper，the experiments of neutron irradiation followed by γ-ray exposure and γ-ray exposure followed by neutron irradiation are conducted with the Xi’an pulsed reactor and the irradiation facility of ⁶⁰Co，taking the bipolar circuits，transistors，and diodes as the experimental subjects.The experimental results demonstrate that，for bipolar process circuits，the damage induced by the neutron irradiation followed by γ-ray exposure is more severe than that caused by the γ-ray exposure followed by neutron irradiation.Tests with diodes and gate-controlled transistors are also carried out，which demonstrates that the interaction between the defects generated by the neutron/γ synergistic effects，or between the radiation and pre-existing defects，is relatively weak.This is mainly because the neutron irradiation facilitates the migration of hydrogen from the passivation layer into the oxide layer，which subsequently accelerates the generation of interface trap charges during the total dose irradiation.These findings provide significant insights for the radiation-hardened design of bipolar devices and the assessment of their performance in mixed radiation fields.