The beginning of the research on cosmic rays

Everything in life has a beginning and science, and all of its areas, has a beginning as well. This is the case of cosmic rays research too, but what are cosmic rays? In a simply way, they are subatomic particles, smaller than atoms such as their constituents like protons, that come from the outer space moving at speeds close to the speed of light

Victor Hess

Victor Hess

While studying radioactivity at the beginning of the 20th century, it was found that when an electroscope, that is a devise to determine whether body has electrical charge and its sign (positive or negative), was put close to a radioactive source, the air was ionized, that is that the atoms and molecules of the air were charged electrically. If the electroscope was put far from the radioactive source, it was fount that the air was also ionized, therefore it was thought that it was due to the existence of natural radioactive sources in the surface or the interior of the earth ant that this ionization should decrease at higher altitudes.


How an electroscope works

In 1910, Austrian physicist Victor Hess, climbed up the Eiffel tower in Paris with an electroscope in order to try to determine at what altitude ionization was negligible or non-existent. The result was amazing, because instead of decreasing, ionization increased with altitude. As with any other scientific result, that has to be supported with multiple evidences and various experiments repeated, when possible, in different conditions, Hess repeated its experiment but an altitude of 5000 m! For it, in 1912 he used a hot air balloon but this time with an ionization chamber.

An ionization chamber basically is an instrument with a gas inside between two metallic plates, which are applied a voltage. When the gas inside the instrument is hit by, for instance, a cosmic ray, the ions generated inside the gas move towards the metallic plates because of the voltage in a way that an electrical current, that can be measured, is generated.

The results that Hess obtained were the same as those in the Eiffel tower, thus he arrived to the conclusion that the radiation causing the ionization of the air was not coming from the ground but from above. The name of cosmic rays, is not from those days but from 1932 when Robert Millikan named in this way the radiation coming from the outer space as he thought that they were gamma rays, the most penetrating electromagnetic radiation known to date, although later was discovered that it was not electromagnetic radiation but mostly particles with mass.

From Hess’ discovery, the history of cosmic rays has advanced a lot until nowadays.

Dimitri Skobelzyn used the cloud chamber to detect the first traces of the products of cosmic rays in 1929, as well as Carl Anderson did in 1932 to discover the positron, which is the electron anti-particle (but it is not the proton, because, although it has positive charge, it is 2000 times heavier than the electron).

Later in 1938, Pierre Auger, having placed detectors in various distant points in the Alps, detected that the arrival of particles in both detectors was simultaneous, so he found that the impact of high energy particles in the higher layers of the atmosphere generated secondary particle showers.

particle shower

Secondary particle shower generated in the atmosphere by the impact of a cosmic ray

Currently the detectors used to study cosmic rays are more sophisticated and, because the intensity of the particles coming from space is higher at higher altitudes, they are located in mountains and elevated areas as it is the case of the Pierre Auger observatory in the Pampa Amarilla in Argentina with an average altitude over the mean sea level of 1400 m or the MAGIC experiment in the Roque de los Muchachos observatory in the Palma Island of the Canary Islands (Spain).


Telescopios del Experimento MAGIC en el Roque de los Muchachos

Our detectors are even in the space like the Alpha Magnetic Spectrometer, also known as AMS-02 installed in the International Space Station whose objective is to measure the antimatter of cosmic rays to search for eviden of dark matter.


Arqueros F. Rayos Cósmicos: Las Partículas más Energéticas de la Naturaleza. Revista “A Distancia (UNED), 1994.

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