Japan's nuclear leakage has become the focus of global attention. The "butterfly effect" caused by the nuclear accident makes people panic about nuclear radiation spreading all over the world. The shadow of "discussing the discoloration of radiation" caused by "discussing the discoloration of nuclear radiation" has also been quietly shrouded in people's hearts. At the same time, the safety inspection industry is also carrying out a heated discussion on the "dose rate of leakage radiation" of X-ray safety inspection equipment. With the increasing intensification of international terrorist activities, governments of all countries have strengthened public security precautions. X-ray safety inspection equipment for detecting dangerous goods and contraband hidden in luggage is widely used in airports, customs, railways, metros and other public places because of its intuitive imaging, which can effectively highlight the display of knives, explosives, drugs and other contraband goods, and thus more and more into the public eye. As an important index to measure radiation and environmental safety, radiation dose rate is not only a simple value reflecting the radiation leakage level of X-ray safety inspection equipment, but also a respect and protection for public safety faced by security inspection equipment manufacturers. So, as a manufacturer in the responsibility and obligation to reduce public concern, is it necessary to blindly pursue the lower the dose rate of radiation leakage, the better? In this regard, this paper will also focus on the topic of "dose rate of leakage radiation" which we are concerned about.
Question 1: What is the dose rate of leakage radiation?
The radiation safety index of X-ray usually includes the single checking dose of equipment and the dose rate of radiation leakage.
In the National Standard GB 15208.1-2005, Part 1: General Technical Requirements for Micro-dose X-ray Safety Inspection Equipment, the single inspection dose of the equipment is defined as "the X-ray dose absorbed by the object under inspection once, the unit of single inspection dose is Gy, 1Gy = 1J/kg". The radiation dose rate of the equipment is expressed by the specific kinetic energy rate of air, which is expressed as the unit of ionizing radiation intensity that passes through the radiation shielding protection in unit time and leaks out to the outside of the equipment, and is expressed as muGy/h.
The radiation safety index proposed by GB 15208.1-2005 for the micro-dose X-ray safety inspection equipment is that the single inspection dose of the equipment should not be greater than 5 UG Gy, and the X-ray leakage dose rate should be less than 5 UG Gy/h at any place (including the entrance and exit of the equipment) 5 cm away from the external surface of the equipment, which meets the requirements of GB17060-1997 3.1.
If the X-ray safety inspection equipment meets the national safety standards, the dosage that human body can be irradiated should be less than 5 UG Gy. To illustrate with the commonly known values of CT and X-ray, the standard dose of CT scanning is 35mGy (35000mGy), and the standard dose of X-ray fluoroscopy, which is often done in our physical examination, is 50mGy (50000mGy).
From the above data, we can see that the radiation dose value of security equipment can be said to be insignificant, and the irradiation time and distance are also the key factors determining the absorbable dose of the body. Unlike medical X-ray instruments, X-ray security devices in public places are safe and reliable, and need not worry too much. Even for special groups such as pregnant women, if they spend a short time near the X-ray machine and take necessary distance protection, they have little impact.
Question 2: What are the factors affecting the "dose rate of leakage radiation" of X-ray safety inspection equipment?
On the basis of ensuring the resolution and clarity of the generated image, X-ray safety inspection equipment requires certain voltage of the radiation source and tube, so the amount of radiation produced is also certain. In order to reduce the radiation leakage dose rate, shielding protection measures can only be used.
Technically speaking, the shielding protection adopted by manufacturers of security inspection equipment refers to the use of substances with high atomic number, commonly used lead or lead-containing substances as barriers to absorb unnecessary x-rays.
There are two main areas of radiation protection for general X-ray safety inspection equipment:
One is the lead curtain at the entrance and exit of the detection channel. Its material is rubber or plastic with high lead content, and its lead equivalent is not less than 0.35 mm thick lead plate. It has strong X-ray protection function, can effectively reduce the X-ray leakage and avoid X-ray radiation to staff.
Another * the main place is the passage plate, which is composed of steel plate and lead plate. The lead atoms of lead metal lattice structure of lead plate have a large number of atomic masses and a very compact atomic structure. It has a strong X-ray protection effect. It can effectively reduce X-ray leakage and reduce X-ray radiation to staff.
Therefore, the protective effect of lead curtain and passage plate has become an important factor to determine the "dose rate of leakage radiation" of security inspection equipment, especially the thickness of lead plate in passage plate plays a vital role.
Question 3: Is the smaller the radiation dose rate, the better?
As mentioned in the previous section, the thickness of lead plate in the channel plate is a key factor in determining the "dose rate of leakage radiation". So, in order to reduce the radiation leakage dose rate of equipment, it is necessary to blindly increase the thickness of lead plate?
In fact, it is not a good thing to go to this extreme. On the one hand, excessive use of lead sheets will significantly increase the weight of equipment, and the movement and transportation of equipment will be extremely difficult; on the other hand, as a heavy metal, once discarded into the environment or ecosystem, lead will be retained, accumulated and migrated, which will cause great harm to the natural environment. Therefore, in today's era of advocating green environmental protection, such a practice is bound to be undesirable.
Therefore, as a manufacturer of X-ray safety inspection equipment, while striving to do a good job of equipment radiation protection measures, and strive to reduce radiation leakage dose of equipment, it is also responsible to take into account and take into account the environmental hazards that may be caused by the abandonment of equipment. Only by finding such a balance can we be a qualified and socially responsible good enterprise.
As the general public who will inevitably contact security inspection equipment in public places, it needs to be clear that as long as the security inspection equipment is within the safety radiation standards stipulated by the state, it has almost no impact on the human body! Even pregnant women and other special groups, as long as a little attention, and take the necessary distance protection, will not cause any harm to themselves.
As a purchaser of X-ray safety inspection equipment, it is not necessary to blindly pursue the low and low radiation dose rate of equipment leakage, and some vendors advocate that the radiation dose rate of equipment leakage has even been lower than the natural background level in the air! Therefore, after understanding the basic knowledge of "dose rate of leakage radiation", we believe that we can use a scientific perspective to look at the problem, and wisely identify the advantages and disadvantages of the equipment.