Some time ago, a woman in Chengdu refused security checks and pushed security inspectors down stairs to faint while taking the subway. The woman was detained for 10 days. In reality, there are many people who exclude security checks, but there is no such woman who does extreme things. One of the reasons why we reject it is that we do not understand the principle of security inspection instruments and have some worries. Today, we'll talk about some common and current security equipment.
Security X-ray machine, also known as security machine or baggage security machine. You are all familiar with it. It is the main baggage security equipment in subway and airport. The principle is simple: the ability to use X-rays to penetrate matter. The X-ray penetration ability varies with density, thickness and composition. X-ray machines recognize objects in luggage according to their different penetrating abilities.
Display image of various luggage under X-ray machine
X-ray machine can not only recognize the shape of the object, but also show the color. The color of various substances is different. Organic materials such as paper, clothing, and various foods usually show orange. Mixed materials and light metals, such as those containing sodium, silicon and aluminium, are usually shown in green. Iron, copper and silver are black and blue. The brightness of the above colors depends on the density and thickness of the material.
Many people worry that the food in their bags will be contaminated by X-rays after they have passed through the baggage security machine. There is no need to worry too much about this. The X-ray emitted by the baggage security machine is very low power. It is detected once, and the radiation dose received is less than 5 microshivolt, which is much lower than those used for sterilization and preservation of food by irradiation. Many of the foods we eat are actually irradiated, and so are other countries, such as the Food and Drug Administration of the United States and the United States Department of Agriculture, which have approved irradiation sterilization and preservation of the following foods, such as packaged chilled or frozen red meat, poultry, fresh fruits and vegetables, and cereals.
Security gate, also known as metal detection door. The main purpose is to detect metal sharp weapons carried by passengers. The principle is also very simple, that is, using the principle of electromagnetic induction. There are rapidly changing magnetic fields on both sides of the security gate. These magnetic fields have no effect on human body, but metal is exceptional, because metal will produce eddy current in the rapidly changing magnetic field, and eddy current will produce a magnetic field. When the security gate detects the new magnetic field, the security gate will automatically emit a sound or flash.
The security door flashes when it detects metal on the body.
When many people pass through the security gates, they often feel conflicted and think that it will be harmful to their health, especially pregnant women who are worried about it. Pregnant women care about the fetus in the body, which is very normal psychology, but the safety door is not an X-ray machine, it produces only electromagnetic field, does not produce ionizing radiation. This kind of electromagnetic field is very weak, only about 1 microtesla, which is tens of times different from the 30 microtesla stipulated in the National General Technical Specification for Passing Metal Detection Gates. In addition, we can also think that security personnel have been near the security gate for many years. If the security gate is harmful to human body, we believe that they will not agree.