When talking about radiation, some people may think of the atomic bomb, the Chernobyl accident or the Fukushima nuclear crisis. That’s right, the nuclear radiation in these appalling incidents and the X-rays in the station security devices are both “ionizing radiation” that may affect human health. When the human body is irradiated with ionizing radiation, part of the energy may be absorbed by various parts of the human body, causing molecular ionization, chemical bond breakage, and DNA damage with a certain probability, which in turn triggers physiological reactions of the human body. However, just as there is no need to worry about alcohol poisoning when drinking alcohol in moderation, when the intensity of a certain ionizing radiation is very low, the exposure time of the human body is very short, and the total effective dose is below a certain standard, its health effects can be ignored.
China’s “Ionizing Radiation Protection and Radiation Source Safety Basic Standards” (GB18871-2002) stipulates that the estimated annual average effective dose of artificial radiation to the public cannot exceed 1 mSv. Sievert is a unit that measures the biological effects of ionizing radiation. It is generally believed that the average annual effective dose of natural radiation received by every person in the world is 2.4 mSv. These natural radiations include cosmic rays, ionizing radiation on the earth’s surface, natural radionuclides ingested through diet, and radioactive radon inhaled indoors and outdoors.
Compared with the above two figures, how much is the radiation dose caused by the station security inspection equipment? Since it is impossible to implant dosimeters in various parts of the human body, a paper published in “China Radiation Hygiene” in 2011 used a computer program to simulate the entire process of a person passing through a security inspection device. The author of the article assumes that a person has to go to work 300 days a year, go through security checks twice a day, and it takes 20 seconds to pass by each time. In this process, if the lead curtain at the entrance and exit of the inspection device remains intact, the total amount of radiation this person receives in a year is 1/14,000 of 1 mSv. Even if the lead curtain is severely damaged and three gaps of 5 cm wide are opened, the total amount of radiation this person receives in a year is only 1/120 of 1 mSv. Compared with the natural radiation that cannot be avoided in life, the radiation caused by the inspection device is insignificant.
In order to speculate on the public health effects caused by these small amounts of artificial radiation, let us first look at a set of much larger data.
According to a document on the website of the Institute of Radiation Protection and Nuclear Safety Medicine of the National Center for Disease Control and Prevention, due to geological conditions, the natural radioactivity level in Yangjiang, Guangdong, Southern China, is relatively high. It is surrounded by mountains with granite lithology. In granite, the content of natural radionuclides such as uranium, thorium and radium is relatively high. The rock formations on the surface of the mountain are weathered and washed by rain, so that particles containing natural radionuclides, especially thorium-rich particles, are deposited on the low-lying ground in the area.
The average annual effective dose of natural radiation to residents in some areas of Yangjiang is 6.4 mSv. In other words, the additional natural radiation dose received by a resident in these areas far exceeds the radiation dose received by residents in other areas from security devices.
Scientists not only calculated the average annual effective dose of these residents, but also estimated the individual lifetime cumulative exposure dose. The results did not find that the additional radiation dose had a significant adverse effect on the health of the residents in these areas (including cancer, spontaneous abortion rate, multiple birth rate, infertility rate, neonatal mortality rate, child growth and development, etc.). On the contrary, the data suggests that certain cellular immune functions of these residents have been significantly improved.
Some people are still worried about whether the security inspection device will affect the fetus in the pregnant woman’s womb. It is a matter of medical ethics. This question cannot be directly studied through experiments. We can refer to the radiation dose produced by medical examinations. The International Commission on Radiological Protection’s No. 84 publication pointed out that although the radiation risk in early pregnancy is the most significant, there is a threshold of about 100 millisieverts for the teratogenic effects of radiation. In medical examinations where the effective dose is less than 1 mSv, medical staff can inform pregnant women that “the risk is negligible.” Therefore, pregnant women not only do not need to worry about the security inspection device affecting pregnancy, but also can safely engage in the operation of the security inspection device.
