With the rapid development of the economy, more and more people choose to travel by air, and even there are routes between East Asia (such as Beijing, Seoul, Tokyo) and the east coast of North America (such as New York, Washington) to fly over the Earth's North Pole to save time and fuel. However, while we enjoy the convenient experience of the aircraft, we must also pay more attention to the radiation problems received during the flight.
In 1912, Hess took a balloon to measure air radioactivity and discovered cosmic rays
From 1912, when Austrian scientist Victor Hess discovered the existence of Cosmic Rays through balloons, to 1991, when the International Commission on Radiation Protection (ICRP) recommended that air crews be included in occupationally photographed populations for radiation dose management, the public has also paid more and more attention to radiation. So what is the radiation dose in normal flight? Today Xiaobian will take you to find out.
01 Where does the radiation you receive when you fly come from?
First, let's talk about the sources of aviation radiation.
As a tiny part of the universe, the earth is bathed in cosmic rays all the time. Cosmic rays are tiny particles with the ability to penetrate. These tiny particles with penetrating power can be divided into two types, one from the distant outer solar system (the Galactic Cosmic Ray) and the other from the sun that gives us light (the sun's high-energy particles).
Radiation in space
Galactic cosmic rays are high-energy particles derived from outside the Solar System and flooded the Milky Way. There are a large number of high-energy electrons in the supernova remnants, which are the birthplace of cosmic rays of high-energy electrons. It is widely conceived that supernova explosions and their remnants will produce high-energy nuclei. Supernova explosion shocks can accelerate cosmic rays. Essentially, supernovae are like giant natural particle accelerators. Earth is often exposed to the galactic cosmic line.
Remnants of supernova explosions
The other category is solar high-energy particles, which are high-energy charged particles emitted during solar storms. Through observations in space or on the ground, it can be found that the flux of high-energy particles will suddenly increase violently in tens of minutes to several days, and then gradually decay to the background level, this rubber band-like sudden rupture phenomenon will release huge energy, because the vast majority of solar high-energy particles are protons, also known as solar proton events. Solar proton events occur more frequently during solar activity.
Coronal mass projectile phenomenon
Particles in cosmic rays are called primary particles, mainly protons, small amounts of helium, and very few other heavy nucleated ions. Because the Earth is covered with a thick atmosphere, primary particles hit the nucleus of the atmosphere to produce protons, neutrons, leptons, and photons (γ rays). These secondary particles reproduce to produce more secondary particles until the average energy is equal to some critical value, the number of secondary particles reaches a maximum value, after which the particles gradually decay or are absorbed by the atmosphere, causing the number of secondary particles to gradually decrease, a reaction called "air clustering". The radiation dose at the altitude of aviation flight is mainly generated by secondary particles, where the radiation dose produced by neutrons accounts for more than 50% of the total radiation dose.
Schematic diagram of air clustering
02 Can cosmic rays reach the ground and touch us?
Because the Earth is protected by a magnetic field, charged particles bounce between the poles, forming two huge doughnut-shaped bands of high-energy electrons and high-energy protons. Earth's magnetic field can also deflect some cosmic rays, thus protecting us from solar storms.
Schematic diagram of the Earth's radiation belts
The Earth's magnetic field protects the Earth
But there are also cosmic ray particles that "sneak into" Earth's magnetic maximum atmosphere to produce dazzling, colorful auroras. These high-energy particles collide with and excite atoms and molecules in the atmosphere, producing light and forming auroras.
The Antarctic Aurora captured by the aircraft
Aurora Aurora, USA
Cosmic radiation is the ionizing radiation produced by primary photons and α particles outside the Solar System when they interact with the composition of the Earth's atmosphere. But only a fraction of this radiation is ultimately able to carry some of the remaining energy to the various creatures that live on the Earth's surface.
The Earth's atmosphere absorbs radiation
Although most of the rays have been blocked out, the creatures on the Earth's surface are exposed to rays all the time. In the space environment, the intensity of cosmic radiation exceeds the range that the human body can accept, which will cause human beings to be unable to survive normally. The intensity of cosmic radiation on the ground is within the range that can be directly accepted by human beings.
03 Different routes receive different amounts of radiation
The effect of cosmic rays on the human body depends on the amount absorbed, the type of particles, the energy, and the specific body part. The health risk of radiation is generally measured in the biological radiation unit Westwert (Sv), and 1Sv means that there is a 5.5% chance of eventually developing radiation-induced cancer later in life. It is generally believed that the average annual effective dose of natural radiation received by the average person in the world is 2.4 mSv, which includes cosmic rays, ionizing radiation from the earth's surface, natural radionuclides ingested through diet, and radioactive radon inhaled indoors and outdoors.
The size of the radiation in everyday life
Some of the radiation sizes common in our lives are: 0.25 μSv (1 mSv = 1000 μSv) for an airport security check; 0.05 mSv for cosmic rays on a transoceanic flight, which can increase tenfold when solar activity is intense, and the radiation received by people flying all year round can reach several mSv a year.
But as far as flying is concerned
Different routes are exposed to different amounts of radiation
1. The first is the relationship between the altitude of the flight and the level of radiation. When the flight altitude is higher, the more radiation is exposed. For example, a small aircraft that flies at an altitude of about 7.5 kilometers is exposed to about 10 times more radiation than sea level. If it is a large aircraft flying at an altitude of 12 kilometers across the ocean, the amount of radiation received is about 40-50 times that of sea level.
Relationship between radiation and height
Why is there more radiation at high altitudes? The main reason is that the closer we get to the source of cosmic radiation, the less space-line and Earth protect our atmosphere. Cosmic rays colliding with molecules in the air cause them to split into smaller, lower-energy particles. As these particles continue to divide, they have less and less energy when they reach the surface. So if there isn't enough of an atmosphere to protect us, we're exposed to even more radiation.
2. In addition, the latitude at which the flight is located will also affect the amount of radiation. Cosmic rays can strike the Earth from all directions, but we are not exposed to radiation at different latitudes. This is related to the second line of defense against cosmic rays, the Earth's magnetic field. The Earth's magnetic field is like a shield that can deflect some cosmic rays. Due to the shape of the magnetic field, cosmic rays hit the atmosphere perpendicular to the magnetic field at the equator, and the atmosphere near the equator tends to be thicker, so cosmic rays are best shielded at the equator.
Relationship between radiation and latitude
The north and south poles are hardly shielded. Cosmic radiation levels in the polar regions are about twice as high as in the equatorial regions. Still, people living in the polar regions are protected by the atmosphere from most cosmic rays. However, the polar regions are exposed to more radiation than the equator when flying.
In terms of flight, different locations are exposed to different levels of radiation: the radiation from high altitudes is higher than that of the ground, the radiation of polar flights is higher than that of non-polar flights, and more radiation does increase the risk of carcinogenesis.
But don't panic, although the polar route radiation is relatively high compared to the general route, it does not exceed the standard! Studies have compared the doses of radiation to polar and non-polar air crews. Statistics show that the annual effective dose of polar air crew is 5.79mSv/a, and the annual effective dose of non-polar aircrew is 2.14mSv/a. Below the current IAEA dose limit (20 mSv) for annual radiation for occupational reasons.
conclusion:
Arctic flights do increase radiation exposure, but they do not constitute an additional excess dose, which is basically a normal route flight without psychological panic.
The image comes from the relevant network
bibliography:
[1]https://www.zhihu.com/question/35397295/answer/62774228
[2]https://www.guokr.com/article/436840
Wang Xinyue. Effect of cosmic radiation on civil aviation flight[J]. Science & Technology Horizons, 2017, 000(009):156-157.
Tuo Fei, Yao Yongxiang, Zhou Lian, et al. Comparison of photon and neutron cosmic radiation doses received by air crews on polar and non-polar routes[J]. Chinese Journal of Radiation Medicine and Protection, 2010, 30(4):469-471.
Editor: Wan Peng
Editor: Wang Wanyu
Proofreader: Wang Haibo