"Big bags, small bags, please go through security check!" Security check is always an essential step when you travel by high-speed rail, airplane, or subway. I wonder if you have ever been interested in this security check machine. What can the staff see on the screen? How do they quickly identify the items in the suitcase? Today, let the editor reveal this secret for you.

How does the security inspection machine work?

Generally speaking, the machine that conveys and inspects luggage is called an X-ray luggage inspection machine. As the name suggests, the security inspection machine uses X-rays to inspect luggage.

X-rays are short-wavelength electromagnetic waves that can penetrate objects. The penetration of X-rays varies depending on the thickness, density and material of the object.

Everyone should know that X-rays in hospitals are also used by doctors. The penetration rate of X-rays varies according to the density of the structure and tissue. The penetration rate is high in loose areas and low in dense areas. The bones of the human body are denser than the skin and flesh tissue. Therefore, when X-rays are irradiated to the human body, the outline of the bones will be displayed more clearly on the screen.

The same is true for the security inspection machine that checks luggage. The penetration rate of X-rays on different objects is different. When the suitcase passes through the security inspection machine, the X-rays penetrate the suitcase and display the outlines of different objects on the display screen.

At this time, some friends may feel confused: X-ray imaging should be black and white, so why can security inspectors identify different objects so quickly?

This question really hits the nail on the head. If you have ever looked at the security check display screen, you will find that the image on it is in color, not black and white.

Normally, the color of the image formed by X-rays on the film is indeed black and white, just like the X-ray photos in the hospital. The reason why a color image appears on the security screen is that the computer calculates and converts the projection intensity of the X-rays. This is also to make it easier for security personnel to quickly distinguish different objects in a short period of time.

Normally, orange represents organic matter such as liquids and sprays; blue represents metals and various controlled knives; and heavy metals or lead, which can completely absorb X-rays, will be displayed in black.

Now you should know why the staff will immediately notice and ask you to take out a small pair of scissors in your suitcase; and the water in your backpack will also be asked to take out and drink a sip.

Will security inspection machines cause radiation hazards to the human body?

After talking about luggage security inspection, let's talk about human security inspection. Generally, two types of instruments and equipment are used for human security inspection: one is a handheld security inspection device, and the other is a security inspection door.

Neither of these two devices emits non-ionizing radiation like X-rays, and their working principle is mainly to detect metal objects on passengers through electromagnetic induction.

If there are metal objects on the passengers, the surrounding magnetic field environment will change, and then the relevant equipment will sound an alarm. The radiation they produce is of the same type as that produced by mobile phones, and the radiation dose is 100 times smaller than that of mobile phones, so there is no need to worry about them causing harm to human health.

Then everyone may ask: The working principle of the luggage security machine mentioned above is X-ray, so doesn't it also produce radiation?

Regarding this question, the inventor of the security machine has already thought about it for us. We are passengers and do not need to go through the luggage security machine, so we only need to consider the radiation around the security machine. Therefore, the shell and protective curtain of the security machine are usually made of lead, and X-rays cannot penetrate lead, so it can effectively prevent X-rays from escaping outside the shell, thereby avoiding the public from being exposed to X-rays.

However, there have indeed been cases of people sneaking into security machines to check luggage. These incidents mostly happened to curious "naughty children" who would sneak into luggage security machines when their parents weren't paying attention. However, there was also an incident in Dongguan, Guangdong where an adult sneaked into a security machine. What happened?

At the beginning of 2018, a figure resembling a human figure appeared on the display screen of a baggage security machine at Dongguan Railway Station, shocking the security personnel.

This was a female passenger. She first put the large luggage she carried into the baggage security machine, and then went through the security check with her small leather bag. However, the security personnel reminded her that she should also put the small bag into the baggage security machine. The passenger's small bag contained a lot of cash and valuables. Because she was worried that the money in the small bag would be lost, she also went into the security machine to "guard" her money at all times. It was really ridiculous.

So the question that everyone is most concerned about now should be whether this will cause radiation damage to the human body. The answer is no, because the radiation level of the security check machine is much lower even compared to medical examinations, and it will naturally not cause any harm to the human body. Therefore, even if you "drill" through the security check machine several times, you don’t have to worry too much.

So how much impact will security checks have on us? Let's let the data speak.

Let's take a 7-day trip during the National Day holiday as an example. Assuming that the 7-day itinerary includes flight-high-speed rail-destination-high-speed rail-flight, and taking the subway twice a day, then there will be a total of 4+2×7=18 security checks, and the time before and after each security check is about 20 seconds.

According to relevant national standards, the ambient radiation dose equivalent at 0.1 meters from any accessible surface of a closed device should be less than or equal to 1 microsievert/hour (the dose equivalent of 1 second is 1 microsievert ÷ 3600 seconds). So, we can calculate that the maximum radiation dose received by each person during the 7-day tour is about 1×18×20÷3600=0.1 microsievert.

Therefore, if we take 10,000 such 7-day tours a year, the radiation received by our human body will exceed the national standard.

Now, everyone knows how little radiation there is during security checks, but in line with the principle of "avoid as much as possible", everyone should leave quickly after picking up their luggage at the security check equipment exit, and do not stay too long at the security check equipment entrance;

Especially for parents who take their children out, parents must keep an eye on their children, do not let them get into the security check equipment, and do not put their hands into the lead curtain at will.

In conclusion

In today's society, security checks have been increasingly widely used in all areas of society. Not only airports, train stations, and subway stations require security checks, but also large tourist attractions, amusement parks, and other places. Security checks have gradually become an indispensable step.

After all, safety is life. If there is no security check, people's life safety cannot be guaranteed. Then people will be walking on thin ice wherever they go. Only when life safety is guaranteed can we talk about other things.