Radiation may remain in the body for 1-3 days, and a person who has received radiation exposure will be radioactive for 1-3 days. If you come in contact with other people within these 1-3 days, you may expose other people to radiation as well. Radiation damage to the human body is a cumulative dose, and even if the previous radiation no longer remains in the human body, it is still counted in the cumulative dose. That is, if the radiation dose to the human body afterwards accumulates to a certain level, it will cause damage to the human body. At present, there are many imaging examinations in medicine, including X-ray, CT or nuclear medicine examinations, and radiation therapy for malignant tumors. So after receiving these examinations or after receiving radiotherapy for a period of time, patients carry radiation.