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Dosimetry of cosmic rays

In the internet, one can find many questions from the public that are aimed on their exposures during flights onboard aircraft. Most of the questions are connected with exposures of pregnant women. Nevertheless, concerns which are subjects of their questions are often not that high as they seem to be. Therefore we decided to write this short simplified explanatory page for all of you, who may feel necessity to determine radiation risk of the travel with plane. 
In the end of the text you will find an estimation of radiation dose obtained during your flight. 
This page has only informative character and the author does not take any legal responsibility for the accuracy, completeness, or usefulness of the information herein. 

Ionizing radiation in short
For most of people, the ionizing radiation (IR) term is connected with the yellow-black radiation danger sign placed on the door of the hospital room with roentgen or computed tomography devices.Less people know that the ionizing radiation is surrounding us during the whole life. It origins as a result of radioactivity of various elements contained in the Earth’s crust or as a result of impact of cosmic rays on Earth. Some of these nuclides even leek from the ground as gases and penetrate into buildings. Well known example of such a gas is for example Radon–222 (222Rn).  All these sources are generally denoted as natural radiation sources.
Besides natural sources, mankind produces ionizing radiation in various parts of its activities, from nuclear energy through medicine up to military. All this sources are commonly denoted as artificial.

Cosmic rays
One can define cosmic rays as ionizing radiation originating in space and impinging on the planet Earth. We distinguish two main components: solar and galactic. Cosmic rays are primarily composed of high energy protons (approximately 85%) and alpha particles (10%).   Remaining components can be ionized nuclides of all known atoms.
When the cosmic rays pass the atmosphere, they undergo many interactions with molecules of the air (including nuclear interactions). In these interactions, new types of particles are often born and interactions result in attenuation of the primary cosmic rays. In fact, this is the way, how the atmosphere protects us from the negative influence of the cosmic rays.
Besides the atmosphere, the Earth is protected by its magnetic field. However, the shape of the magnetic field lines causes that protective effect of the magnetic field depends on the geographical latitude. The shielding effect is maximal near equator and minimal in the region of magnetic poles. In the magnetic poles region, the high energy particles of cosmic rays penetrate into the bottom layers of the atmosphere, ionize the air and induce aurora borealis lightning.
In generally, the cosmic rays flux grows with increasing altitude and geographical latitude. And this reason is the cause of higher exposures of passengers and aircrew onboard aircraft.
 
Biological effects of ionizing radiation.
Biological effects of the ionizing radiation are very complicated complex topic interconnected through various scientific fields. In generally, the most dangerous effect of the radiation is the damage of genetic information saved in the DNA. Fortunately, live organisms are well prepared for such damages, which are induced not only by radiation but also as a result various chemical interactions. Typical human organism performs several millions of such a repair daily.
Generally, we distinguish two kinds of biological effects of ionizing radiation – stochastic and deterministic. Deterministic effects of the radiation are connected with relatively high radiation doses of orders from several hundreds of miliSieverts to several Sieverts (Sievert – unit of effective dose; shortcut of the unit is Sv) and the effects of such an radiation occur usually within several hours. One can state “acute radiation syndrome” as an example. Stochastic effects of the ionizing radiation do not occur immediately and are expressed with a probability. This probability expresses relative amount of cases, in which the specific obtained radiation dose will result in specific time into a specific (negative) health effect. Stochastic effects are always connected with relatively low doses usually within the range from tenths up to hundreds of mSv.
And how can we protect against the stochastic effects of the radiation? The most important is to ensure sufficient income of healthy food rich on antioxidants and vitamins.

Comparison of typical radiation doses
Table bellows present typical doses from ionizing radiation received from some common medical examination procedures. Values are also compared with the time that is necessary to obtain exactly same dose from natural radiation in the Czech Republic.

 ActivityTypical effective dose [mSv]
 Approximate time necesary for the same exposure from natural radiation at Earth*
 Skull X-ray
 0.07 11 days
 Limb X-ray
 <0.01 <1.5 days
 Mamography <0.1 15 days
 Abdomen X-ray
 1.0 5 months
 CT of skull
 2.3 1 year
 CT of abdomen
 10 4.2 year
 CT of breast and abdomen
 17.2 7.2 year
 Flight Praha - New York
 0.037 5.5 days
 Flight Praha - Moskva
 0.009 <1.5 days
 Flight Praha - Sofie
 0.004 1 day
 Limit of A cathegory of radiation worker in EU
 20 8.7 years
 Typical year effective dose from natural sources in CR
 2.38 1 year
 Limit for pregrnant aircrew member in EU
 1 5 months
* Mean effective dose from natural radiation used for the calculation is 2.38 mSV

Estimation of radiation dose during the flight
One can estimate the dose received from cosmic radiation during a flight as follows:

Dose = flight duration [hours] x 0,004 [mSv]

Formula above can be used for most of flights above the Europe or close to the equator. Nevertheless, the calculation is necessary for other routes or more precise value of the dose.
If you wish to calculate the dose more precisely, write an e-mail to kubancak@ujf.cas.cz . Message must contain information about:
•    departure airport
•    destination airport
•    date and time in ISO format (YYYY-MM-DD hh:mm)
•    number of the flight (e.g. OK-372)

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