Train station security machines can detect metal and prohibited items.
In fact, detecting images of people was originally one of the functions of the screening machines. In the detection of containers in large ports, X-ray security equipment is the detection of stowaways. Now the main principle of the common security equipment are the use of physical and chemical methods, for some substances for specific signal capture, so as to carry out the detection of morphology and composition.
For example, the common security gate, hand-held metal detector, is the use of metal conductors by the alternating electromagnetic field excitation in the metal conductor generated by the eddy current, the eddy current detection and thus found metal objects; airport entrance to detect traces of explosives, "rubbing paper", is the use of different ingredients The molecules in the applied electric field drift speed (with " mobility " expressed) of the different composition detection.
Particularly good at distinguishing between drugs, explosives and other organic macromolecules; while in the suspicious liquid detection, is the use of the medium in the electric field under the action of polarization (with the "dielectric constant" expressed in different) to distinguish between low dielectric constant of flammable liquids. Of course, most of the time, people choose the easier way "try a sip".
(Common security equipment) Among the many security equipment, the earliest and most widely used is still X-ray detection equipment. After the news of the female passenger who entered the screening machine mentioned above appeared, some experts suggested that the X-ray radiation from the screening machine is harmful to the human body, so how much harm would it do to her? In the network, the safety of security check machine radiation had been rumors.
There were even concerns that food would spoil after being irradiated. In fact, although the same is the use of X-rays to irradiate the object to be detected to obtain the internal image of the object, but the radiation of the security machine is far less than the medical X-ray equipment. This is mainly because the security equipment does not need to achieve medical diagnostic level of resolution, only for different substances to distinguish between imaging.
According to the national standard GB15208.1-2005, the single inspection dose of the X-ray security checker should not be greater than 5μGy/h (current radiant energy, absorbed dose unit), and at the same time in the distance from the outer surface of the device 5 cm from any position (including the entrance and exit of the device), the X-ray dose should be less than 5μGy/h, the standard with the U.S. FDA's standard is the same.
In fact, the X-ray radiation dose of the screening machine is much lower than the national standard, a brand of X-ray screening equipment used in the Beijing subway, for example, according to the company's technical data show that the radiation dose of a single detection in 0.5μGy, 5 cm outside the surface of the radiation dose of 0.7-0.8μGy/h, only one-tenth of the upper limit of the national standard.
A medical X-ray chest X-ray radiation dose of 50μGy. If you have to compare the two, drilling into the security machine 100 times in order to achieve a chest X-ray radiation dose. Of course, the radiation dose is not simply superimposed, just like soaking in a hot bath of 40 ℃ for an hour is not the same as soaking in a hot bath of 80 ℃ for half an hour, and their effects on the human body are completely different.