Discovery of cosmic rays• In 1909 Theodor Wulf developed an electrometer, a device

to measure the rate of ion production inside a hermetically sealed container, and used it to show higher levels of radiation at the top of the Eiffel Tower than at its base. However, his paper published in Physikalische Zeitschrift was not widely accepted. In 1911 Domenico Pacini observed simultaneous variations of the rate of ionization over a lake, over the sea, and at a depth of 3 meters from the surface. Pacini concluded from the decrease of radioactivity underwater that a certain part of the ionization must be due to sources other than the radioactivity of the Earth

History of Cosmic Rays: 19121912 Victor Hess

Investigated sources of radiation – took balloon up to 5000 meters

Found radiation increased after 2500 meters

This could be attributed to the fact that there was less atmosphere above to shield him from radiation

Thus he discovered that radiation is coming from space ... “cosmic radiation”

Won Nobel Prize in 1936

Hess after his flight, which he took without breathing apparatus in very cold and thin air!

• In the 1920s the term "cosmic rays" was coined by Robert Millikan who made measurements of ionization due to cosmic rays from deep under water to high altitudes and around the globe. Millikan believed that his measurements proved that the primary cosmic rays were gamma rays, i.e., energetic photons. And he proposed a theory that they were produced in interstellar space as by-products of the fusion of hydrogen atoms into the heavier elements, and that secondary electrons were produced in the atmosphere by Compton scattering of gamma rays

• . But then, in 1927, J. Clay found evidence, later confirmed in many experiments, of a variation of cosmic ray intensity with latitude, which indicated that the primary cosmic rays are deflected by the geomagnetic field and must therefore be charged particles, not photons. In 1929, Bothe and Kolhörster discovered charged cosmic-ray particles that could penetrate 4.1 cm of gold. Charged particles of such high energy could not possibly be produced by photons from Millikan's proposed interstellar fusion process.

Post MSc Lectures, December, SINP

What are cosmic rays ? • High Energy particles

• Fully ionised atoms (98%, mainly Hydrogen and He)

• < 1% Electrons and photons• Secondaries : high energy particles

generated by interactions of cosmic rays in atmosphere

• Achtung : more than 50,000 of such particles are going through you in < 30 mins

• Particle identification in tracks of emulsion plates• Development of Geiger counters, Cloud chamber

• Birth of Particle Physics in Cosmic rays ( 1920 to 1940 )

What are cosmic rays (CRs)?• As it turns out, these charged

particles are atomic nuclei zooming through space– Called “primary” CRs– Mostly protons or a (He) nuclei

(other elements too, in much shorter supply)

– There are more coming in at lower than higher energies

• When these hit another nucleus in the atmosphere and stop, more particles are knocked downward, causing a cascading effect called a “shower”– Particles in the shower are called

“secondary” CRs

Crab nebulaمركب....ة ص....ورة :  ص........ور لثالثاألشع...ة  ص...ورةتح..................ت ) أحم....ر) الحمراء   مقراب خالل م.نس..............بيتزر الفضائ..........ي، الضوء  ص.......ورة ) ( ، أخض.ر المرئ.ياألشع..ة  وص..ورة ) أزرق ) الس...ينيةمس..ييه " لس..ديم

مص..ادر" 1 ت..بين ،تل.....ك إص.....دارم....ن اإلشعاعات

السديم.

Keplers supernova

Large Magellanic Cloud