Cosmic rays, detector background measurement

Cosmic rays is ionizing radiation, which falls on Earth from space. Cosmic rays has the smallest wavelength and the highest frequency of oscillation known to us. Its potential energy is also huge. Fortunately for human it is removed largely by magnetic field and Earth´s atmosphere. Only a tiny amount falls on Earth. This amount is compatible with life.

Components of cosmic rays

Cosmic ray spectrum

Cosmic rays is divided into two groups: primary and secundary. Primary cosmic rays are radiation that has no interaction with atmosphere. Its energy is around 10 GeV, but it can be up to 10¹⁸ eV. Secundary cosmic rays is created by interaction of primary cosmic rays with Earth´s atmosphere. It contains almost all elementary particles (e.g. neutrons).

Cosmic radiatio values for the earth and beyond

Intensity of cosmic rays is affected by two factors: altitude and latitude. Its intensity increases up to a height of 20 km with increasing altitude and then to 50 km is decreasing. It is constant at greater distances. The onteresting thing is thatthere is intensity of cosmic rays up to 25% higher at the poles. It is related with orientation of magnetic pole of Earth.

Cosmic radiation in medicine

Cosmic radiation is commonly used in nuclear medicine, where it is involved in running of detector. It forms the so-called ,,background,,. The background is component we are trying to eliminate by shielding. Due to the high radiation energy is not possible to eliminate completely all radiation.

Cosmic rays in other fields

It is logical that people are exposed to cosmic rays, who are outside the Earth ´s atmosphere. Big problems are causing in cosmonautics. It must be kept in mind when designing spaceships. Passengers on airplanes are also exposed to a relatively higher amount of cosmic radiation same as gamma rays or X-rays. However the exposure values are not high so we do not have to worry about any side effects with the proportionate use of air transport means.

Detector background

Three radiation components are used in the background of the detector . The first one is an external radiation from surrounding space. The second one is an internal radioactivity of the material. The third one is an electrical noise of the device. Cosmic rays are present in the first one logically.

References

• BENEŠ, Jiří – JIRÁK, Daniel – VÍTEK, František. Základy lékařské fyziky. 4. edition. nakladatelství Karolinum, 2015. ISBN 978-80-246-2645-1.

• ULLMANN, Vojtěch. AstroNuklFyzika [online]. [cit. 2016-01-31]. <http://astronuklfyzika.cz/DetekceSpektrometrie.htm>.

External links

ENG wikipedia