"小剂量照射" can be translated into English as "low-dose irradiation" or "low-dose exposure".
"Low-dose irradiation" emphasizes the act of being exposed to radiation at a low level.
"Low-dose exposure" focuses more on the state of being exposed to a low dose of something (in this case, radiation).
Both expressions are commonly used in scientific and medical contexts to describe situations where individuals or objects are subjected to small amounts of radiation.