COSMIC RADIATION AT HIGH ALTITUDES

Air travel is transporting an increasing number of passengers. In 2023, 4.2 billion passengers were carried by airplanes worldwide. Cosmic radiation, composed of high-energy particles, loses energy gradually as it travels from space toward the Earth, colliding with particles in the atmospheric layers, which reduces its intensity (or flux). The Earth’s magnetic field deflects cosmic radiation in the Equatorial Region, significantly reducing its effect, especially between latitudes 0° and 30°. As one moves toward the poles, the magnetic field weakens, so cosmic radiation is less deflected and its impact increases in those areas. .

Since the intensity of cosmic radiation is higher at the altitudes where we fly in airplanes, it is expected that its effects on our bodies will also be greater. Figure 1 shows that the cosmic ray dose (or cosmic radiation dose) increases with altitude. The ‘effective dose rate’ in microsieverts per hour (µSv) is only 0.03 at sea level, whereas at the 10–12 km altitude where we fly with airplanes, this value rises to approximately 8 µSv, or 260 times that at sea level. .

Cosmic Rays.

Physicists first noticed cosmic rays during laboratory studies while investigating why electrically charged objects gradually lost their electric charges. Initially, they thought the effect originated from naturally radioactive materials in the Earth’s crust. Eventually, Austrian physicist Victor Hess, in 1912, rode a balloon and observed his electroscope’s indicator, noting that as he ascended, the electrical charge gradually decreased. He concluded that something hidden was coming from the sky, from space, ionizing the air, and thus the charges on the electroscope gradually decreased. This hidden agent was called ‘cosmic rays’ (Hess later received the Nobel Prize in 1936 for his research and this discovery). .

In the 1950s, physicists determined that cosmic rays were not composed of light particles (photons) or electromagnetic waves, but rather a continuous ‘ion flux’ consisting mostly of protons at very high speeds and a smaller number of heavier particles. Nevertheless, the term ‘cosmic rays,’ though historically inaccurate, remained. These ‘very fast’ and therefore ‘very high-energy’ protons and ions coming constantly to Earth from the depths of space beyond our solar system are slowed by the dense atmospheric layers they must pass through, generating mesons and many other secondary particles in large numbers from the atoms they collide with, affecting us in the atmosphere and on Earth, including muons that can penetrate deep underground. .

Cosmic rays are fundamentally the same type of ionizing radiation as natural radiation from the Earth’s crust and radiation from nuclear power plants, capable of causing changes and damage in cells, molecules, and atoms in the human body. At low doses, the likelihood of cancer is small, though very rarely DNA breaks may occur. .

Dose Received on Airplanes.

The magnitude of the dose received from cosmic radiation on airplanes depends on flight altitude, flight duration, solar activity (effectiveness), and the geographic (geomagnetic) latitude of the flight path. Due to business trips, many people spend approximately 240 hours per year on airplanes. During this time, the total dose a person might receive, although dependent on the flight route from one part of the world to another, can roughly be estimated as 0.008 x 240 = 1.92 mSv. .

The cosmic radiation dose received varies depending on the departure and arrival locations. For example, Table 1 below shows the variation range of cosmic doses for flights from Frankfurt to various cities (similar dose ranges could apply for Istanbul or Ankara instead of Frankfurt). .

Dose Received by Aircrew.

Assuming that pilots and flight attendants generally work 80 hours per month and 10 months per year, their estimated dose can be roughly calculated as: 800 hours x 0.008 = 6.4 mSv. This dose can be considered a maximum dose. (In Germany, the average value measured with radiation dosimeters for male personnel is 2.9 mSv per year). .



Situation for Aircrew in the EU and Germany.

According to European Union (EU) regulations, for aircrew whose annual dose may exceed 1 mSv, body doses must be determined with ‘dosimeters,’ evaluated, and preventive measures taken if necessary. Aircrew, like nuclear reactor personnel or doctors working with X-ray devices, are classified as ‘radiation workers,’ trained on the effects of radiation on the body, and therefore the annual dose limit of 20 mSv applies to them as well. In EU countries, aircrew doses must be measured according to relevant regulations, calculated and evaluated with appropriate computer programs, and reported to the competent authorities. .

Since 2003, in Germany, the cosmic radiation doses received by all aircrew on registered aircraft (scheduled, charter, cargo, and military) have been calculated and recorded monthly using radiation dosimeters installed on airplanes and relevant dose calculation programs. Between 2004 and 2009 in Germany, the number of aircrew increased by 23% to 36,600 people. During this period, the collective radiation dose received by personnel also increased by 48%, reaching 86 person-Sv. The average annual dose was 2.35 mSv in 2009, with male aircrew receiving the highest average dose of 2.9 mSv. Due to low solar activity in 2009, cosmic rays penetrated the atmosphere more, resulting in higher doses for aircrew. .

In Germany, aircrew receive the highest doses among all personnel exposed to ionizing radiation, including those working in nuclear power plants. Although the highest average dose in 2009 was 2.9 mSv, this value remains well below the 20 mSv annual upper limit for radiation workers. On the other hand, this dose received solely from cosmic rays, when combined with natural terrestrial radiation at sea level with an annual average of 2.4 mSv, means that aircrew remain within the 1–10 mSv range of doses from natural radiation. .

Furthermore, calculations made at the GSF Institute in Munich, Germany, using the specially developed EPCARD computer program, show that for intra-European flights at 11 km altitude, the dose per flight is below 0.010 mSv, less than 0.040 mSv for South Africa and South America, and between 0.050 and 0.080 mSv for Europe–USA flights. .

As a result, the dose received from cosmic rays during air travel and the potential risk should be considered within the same framework as the ‘natural radiation dose’ we constantly receive, along with other radiation doses from technological life (such as X-ray or MRI exposure), relevant regulations should be applied, and excessive or unreasonable precautions should not be taken. .

In Turkey, there are no publications regarding the measurement or personal records of doses received by aircrew, so the situation is unknown. .

Does the Cosmic Radiation Dose on Airplanes Affect Our Health? .

In fact, we all live with natural radiation, including cosmic radiation, from the beginning. .



As seen in Table 2, the annual average radiation dose of 2.4 mSv varies greatly between 1 and 10 mSv, and half of the average dose comes from radon gas, a decay product of radioactive materials (uranium and thorium) in the Earth’s crust. Cosmic rays also contribute more to the radiation dose for people living at high altitudes and during air travel, as can be seen from Figure 1 and the table above. .

The cosmic radiation dose received during air travel is generally equivalent to the dose from a single X-ray examination. This dose, however, is comparable to that received from X-rays in a medical CT scan and carries a very low probability (risk) of causing damage to the body. As a protective measure, aircrew reaching certain limit values are not allowed to fly for a period of time. .

However, the risk may be significant for embryos developing in the womb, potentially increasing the chance of congenital defects. Therefore, pregnant aircrew are not assigned to flights, and pregnant women are advised against long air travel for work or travel purposes. .

Practical shielding or protection against highly penetrating cosmic radiation on airplanes is not possible. Although the risk is very low, with over 4 billion annual travel flights, particularly domestic flights, reducing flight frequency as a protective measure, and opting for sea or land travel, is left to individual choice. Reducing flights also contributes to protecting the atmosphere from greenhouse gases (CO2). .

Note: This text is quoted from the article titled “Cosmic Radiation Dose We Receive on Airplanes and Our Health?” by Radiation Physicist Dr. Yüksel Atakan on the website www.herkesebilimteknoloji.com