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Cosmic Radiation

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There are many different types of radiation which forms a natural part of the environment in which we live. Natural background radiation can be divided into two sources: cosmic and terrestrial (earth-based). With air flight there is a reduction of exposure to radiation from terrestrial sources and an increase in exposure to cosmic radiation.

What is cosmic radiation?

Cosmic radiation is a naturally occurring form of ionising radiation that arises from outside the earth. It has two components, solar radiation from the sun and galactic radiation from outside the solar system.

Is cosmic radiation the same everywhere?

No. The level of cosmic radiation depends on four factors:

  • Altitude: the earth’s atmosphere substantially shields the earth from cosmic radiation. At higher altitudes this shielding effect decreases, leading to higher levels of cosmic radiation.
  • Geographic Latitude: the earth’s magnetic field deflects many cosmic radiation particles. This shielding is most effective at the equator and decreases at higher latitudes, essentially disappearing at the poles. As a result, there is approximately a doubling of cosmic radiation exposure from the equator to the magnetic poles.
  • Normal Solar Activity: the activity of the sun varies on an 11 year cycle. When solar radiation is high, the magnetic field associated with it deflects some of the galactic radiation away from the earth. As galactic radiation is the main component of cosmic radiation, this means that when solar activity is high the total intensity of cosmic radiation is lower and vice-versa.
  • Solar Proton Events (also called solar flares): occasionally large eruptions of charged particles occur on the sun. These particles travel at high speed through space and if they happen to hit the earth, the cosmic radiation dose may be significantly increased for a short period.

What are the health effects of cosmic radiation?

Cancer is the principal health effect that has been associated with low-dose ionising radiation. As all air travel is associated with increased exposure to ionising radiation, it therefore follows that there must be some increased risk of developing cancer. The increased risk is however, extremely small, given that naturally occurring cancer accounts for 23% of deaths anyway in many developed countries.

For example, a person who flies direct return flights from Hong Kong to New York every two weeks for 20 years has their risk of death from cancer increased from 23% to between 23.11% and 23.14%. This represents an increase in percentage over the normal of around 0.5%, which most people would probably not consider unacceptable. 
Questions have also been raised on the effects of cosmic radiation on pregnancy and the health of the fetus. Based on current knowledge, the limited radiation dose obtained during occasional air travel during pregnancy confers very small risks to the fetus.

How much cosmic radiation is there on a flight?

People travelling in aircraft may be exposed to more ionising radiation because the earth’s atmosphere provides less protection from cosmic radiation at the typical cruising altitudes of commercial aircraft. Exposure also increases the further that the flight path is away from the equator. Therefore, the radiation dose will vary between different flights depending on origin, destination, route, flight level pattern and solar activity at the time. Aircrew and frequent flyers get the most additional exposure because of the extra time they spend at cruising altitudes. 

Most Dragon Airlines flights originate or terminate at low latitudes, so we are more fortunate in this respect than airlines based at higher latitude. An estimate of the radiation dose for a specific flight can be obtained from the following and other websites:
http://www.faa.gov/data_research/research/med_humanfacs/aeromedical/radiobiology/cari6/download/

Some values for flights calculated by computer program are:

Hong Kong - New York

High Solar Activity Year

0.0688 mSv

New York - Hong Kong

High Solar Activity Year

0.0619 mSv

Hong Kong - New York

Low Solar Activity Year

0.0938 mSv

New York - Hong Kong

Low Solar Activity Year

0.0817 mSv

 

Hong Kong - Vancouver

High Solar Activity Year

0.0414 mSv

Vancouver - Hong Kong

High Solar Activity Year

0.0465 mSv

Hong Kong - Vancouver

Low Solar Activity Year

0.0501 mSv

Vancouver - Hong Kong

Low Solar Activity Year

0.0551 mSv

 

Hong Kong - Bangkok

High Solar Activity Year

0.0046 mSv

Bangkok - Hong Kong

High Solar Activity Year

0.0041 mSv

Hong Kong - Bangkok

Low Solar Activity Year

0.0047 mSv

Bangkok - Hong Kong

Low Solar Activity Year

0.0043 mSv

Are there any guidelines on radiation dose limits?

Radiation dose is measured in milliSieverts (mSv). Guidelines concerning radiation exposure have been established by international agencies involved in radiation protection. In general they recommend the following limits for flying:

  • For occupational exposure on commercial air flights (for example pilots and cabin crew) 20mSv per year
  • For the general public on commercial air flights 1mSv per year. This includes flying when pregnant.

Aircrew flying 600-800 hours per year are exposed to 2 to 5 mSv of radiation per year. Most public travellers would not be exposed to more that 1mSv per year. Regular business travellers may however be exposed to more than 1 mSv per year, but if they undertake the majority of their air travel for business, they will fall under the occupational exposure limits. Pregnant women should not be exposed to more than 1 mSv per year.

For additional information please see:

Australian Radiation Protection and Nuclear Safety Agency http://www.arpansa.gov.au/radiationprotection/factsheets/is_cosmic.cfm

Disclaimer

The above content provided by Dragonair is for information purposes only. They shall not be used, copied or republished by any persons except expressly authorized by Dragonair. Dragonair has carefully reviewed the contents and taken all steps we consider reasonable to ascertain their accuracy. We do not claim the contents to be comprehensive on the subject matter and they shall not be relied on by any persons who may have an interest in the subject matter. Neither shall they be treated or substituted for medical advice by any persons in relation to the subject matters. We strongly advise and encourage any interested party to the subject matter to seek qualified professional (medical or otherwise) advice for any concerns that he or she may have in the subject matter of the contents.