According to official website of Sichuan Zhonglian NDT Company, the safe distance of X-ray inspection is:

1, the first statement: about 20 meters. The higher the voltage, the greater the radiation energy and intensity. Intensity is inversely proportional to the square of the interval. In addition, if it is not in the front, it will also be affected by scattered light. If there is no protective equipment on the back of the machine when working, it is best to be about 20 meters. If there is lead plate protection, it is better to be safer at a distance of ten meters, and the reflected dose is much smaller. X-rays are also electromagnetic waves, but the wave length and penetrating power can be very strong. The difficulty of this penetration is related to the density of matter. The density of lead plate is very high, but the density of air is very low, so lead plate can completely block X-rays, but air has no blocking ability. X-rays have different penetrating power to various substances. Using high-density barium cement (that is, cement containing barium sulfate) can also shield X-rays horizontally. According to GBZ117-2006 Radiological Protection Standard for X-ray Inspection, the specific kinetic energy rate of the air in the control area, that is, the operation area of inspection workers, should be 15 microsieverts/hour, while the specific kinetic energy rate of the air in the safety zone of personnel in the monitoring area should be10.5 microsieverts/hour, for several meters. You can know the safe interval by measuring and comparing the monitoring instruments.

2. The second statement: the radius around the flaw detector is not less than 30m, and it is designated as the control area. X-ray flaw detector is unsafe without shielding. The radius around the detector should not be less than 30m, and it should be designated as the control area. Personal dose monitoring equipment and protective articles should be worn, and effective protection should be stopped by reducing the time at the radiographic site, increasing the distance from the radiation source and applying shielding materials such as site topography and equipment.