Radioactive sources refer to radioactive materials that are permanently sealed in the cladding or tightly consolidated in the covering layer and in solid state, except for materials in the nuclear fuel cycle of research reactors and power reactors.

According to the potential hazards of radioactive sources to human health and the environment, radioactive sources are classified into categories Ⅰ, Ⅱ, Ⅲ, Ⅳ, and Ⅴ from high to low, and the lower limit of activity of class V source is the exempt activity of that species.

Class I radioactive sources are extremely dangerous sources. Without protection, exposure to such sources can cause death in a few minutes to an hour;

Class Ⅱ radioactive sources are high-risk sources. Without protection, exposure to such sources for a few hours to a few days can cause death;

Class III radioactive sources are dangerous sources. Without protection, exposure to such sources within a few hours can cause permanent damage to people, and exposure to a few days to several weeks can cause death;

Class IV radioactive sources are low-risk sources. Basically, it will not cause permanent damage to people, but it may cause recoverable temporary damage to people who have been exposed to these radioactive sources for a long time and close;

Class V radioactive sources are extremely low risk sources. It is unlikely to cause permanent damage to people.

Unsealed source workplaces are classified into Class A, Class B, and Class C according to the maximum daily equivalent operation volume of radionuclides (GB 18871-2002).

The safety management of Class A sites refers to Class I sources.

Class B and C sites refer to Class II and Class III sources.