High-altitude "crisis"! How strong is the cosmic radiation that causes cancer in flight attendants?

Recently, a piece of news caught our attention. A Korean Air flight attendant died of stomach cancer, and it was first identified by the relevant Korean authorities as a cosmic radiation injury. What is cosmic radiation? Does long-term flight have a risk of cancer?

01Cosmic radiation: the invisible “invisible killer”?

First of all, it must be said that there are indeed many kinds of radiation in the universe where the earth is located. According to Wikipedia, radiation is the process of emitting or transmitting energy in the form of waves or particles in space or material media. In layman's terms, radiation is a kind of propagating energy, usually in the form of electromagnetic waves or particles.

Although according to the principle of wave-particle duality, electromagnetic waves can often be regarded as particles, or composed of photons, in the scope of classical physics, waves and particles are completely different existences, and their radiation characteristics are also very different.

Speaking of radiation, I always think of the movie "Space Exploration Editorial Department" that was released some time ago. The protagonist always holds an exploration device in his hand, which makes a beeping sound from time to time. This sounding device is a device for exploring particle radiation. Its scientific name is Geiger counter . When particle radiation approaches, it will make a sound and start counting. Of course, the current radiation exploration device looks much more advanced, and it can also display the intensity of radiation particles through an electronic display. This kind of measurement is all for particle radiation.

The protagonist holds an old-fashioned Geiger counter tube

Image source: Douban Movies (official stills)

New radiation measuring device

Image source: provided by the author

In our daily life, we have few opportunities to be exposed to particle radiation. We can only do this by going to the hospital for relevant tests. There are many opportunities to be exposed to another type of electromagnetic radiation, from small things like mobile phones, computers, microwave ovens to large things like communication base stations. However, in comparison, the intensity of these electromagnetic radiations is far less than that of the sun's radiation, so there is no need to worry; what we need to worry about is another radiation threat - cosmic high-energy particle radiation from space.

As a tiny part of the universe, the earth is constantly exposed to tiny particles with penetrating power in the universe. They may be high-energy charged particles emitted during solar storms, or they may be galactic cosmic rays from outside the solar system.

The so-called high-energy particles have a single weight far less than 1 nanogram, so although the speed of movement is close to the speed of light, the energy of a single particle is not large. Electron volts are usually used as the unit of energy measurement. Common high-energy particles include MeV (million) or GeV (1 billion electron volts). Although this amount of energy is not enough to cook an egg, they are still considered high-energy in the family of microscopic particles, so they are called "high-energy particles."

To understand the speed of high-energy particles, let's make a simple comparison: if a cake weighing about 30 grams moves at the same speed as a 1 GeV proton, the kinetic energy carried by the cake is roughly equivalent to the energy generated by the explosion of 1,000 Hiroshima atomic bombs.

Copyright image, no permission to reprint

High-energy particles in the universe can cause harm to the human body. However, thanks to the protection of the Earth's magnetic field and atmosphere, the radiation of high-energy particles reaching the surface of the Earth has been greatly weakened. However, for astronauts, entering the space with strong radiation, they must have a protective spacecraft cabin and extravehicular space suits to block most of the cosmic rays. Researchers will also conduct radiation dose checks on astronauts to ensure their health.

02Is the radiation exposure from flying greater than that from X- rays? Flights through the polar regions require attention

If this is the case, how can flight attendants get cancer? Generally speaking, although the radiation at the altitude of an airplane is higher than that on the ground, it is not fatal. Ordinary people spend little time on airplanes, and the radiation they are exposed to is not enough to cause illness; flight attendants fly all year round, and the radiation dose they are exposed to is definitely higher than that of ordinary people.

We usually use the biological radiation dose unit Sv to measure the health risks of radiation. Taking a chest X-ray as an example, each exposure time is about 0.2 seconds, and the radiation dose is about 0.02mSv (1Sv=1000mSv), while the cosmic ray radiation on a transoceanic flight is about 0.03mSv.

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Due to the particularity of the profession of flight attendants, they are indeed more likely to be exposed to cosmic radiation than ordinary people. This flight attendant with cancer flew an average of 1,022 hours per year from 1995 to 2021, and about half of the routes were long-distance flights to America and Europe via the Arctic. When a geomagnetic storm occurs, high-energy particles in the solar wind can enter in large quantities through the polar regions, producing beautiful auroras. At the same time, the radiation intensity of flying over the polar regions will be much greater than usual. Usually, airlines will choose to avoid polar routes when a geomagnetic storm occurs to protect the safety of passengers on the plane.

Taking into account factors such as long-distance flights and irregular diet, the relevant Korean authorities determined that there was a certain degree of causal relationship between the flight attendant's illness and work. In this way, the conclusion of "cosmic radiation injury" is reasonable . Flight attendants need to control their flight time to avoid excessive radiation. On the other hand, ordinary people also need to pay attention to space weather when flying over polar routes.

03 Radiation: Stop scolding me, I feel wronged too

Seeing this, I am afraid that more people will spread the rumor that "radiation is harmful". So it must be emphasized: Duck doesn't have to! We live on the earth itself, which is surrounded by natural radiation sources. Even you who are reading this article at this moment are also a radiation source.

The human body contains carbon-14 and potassium-40, which emit beta and gamma rays. A person is exposed to about 0.4 mSv of radiation per year - of course, you will also produce trace amounts of radiation to others. The report of the United Nations Scientific Committee on the Effects of Atomic Radiation points out that the average annual radiation dose of natural background radiation to an individual is about 2.4 mSv/year. In China, according to the national standard GB 18871-2002, the annual effective dose for ordinary people is 1 mSv. As long as this limit is not exceeded, there is no need to worry about health risks.

There is also a very "popular" saying in the movie mentioned above: the snowflakes on the old-fashioned cathode ray tube TV are the cosmic background radiation. In fact, the snowflakes may be more of the noise of the cathode ray tube itself, and have nothing to do with the cosmic background radiation. The reason for this misunderstanding may be that we often use similar dot distribution diagrams to represent the cosmic background radiation, which looks a bit like the snowflakes on the TV screen. No wonder some people misunderstand it.

Snowflakes on old TV

Image source: Douban Movies (official stills)

The European Space Agency released a map of cosmic microwave background radiation in 2013 based on data sent back by the Planck space probe. This most accurate panoramic picture to date reflects the conditions in the early days of the universe and almost perfectly verifies the standard model of the universe.

Image source: Xinhua News Agency

Author: Liu Yong, Ambassador of China's Space Science Popularization, Director of the Science Popularization Committee of the Chinese Society of Space Science

Review expert: Zhou Xuzhi, researcher at the School of Earth and Space Sciences, Peking University

Produced by: Science Popularization China

Produced by: China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.