Cosmic Rays a Brief History

1895 – 1910 Emission of penetrating radiation, such as X-rays from elementsDiscovered using photographic techniques.

Roentgen - X-rays , image of bones, application to medicine 1st Nobel prize

Bacquerel - Radiations from radioactive substances such as Uranium ore Observed also by photographic techniques – Nobel Prize

Curies (Marie and Pierre): Natural Radioactivity – nuclear transformationsRadiation unaffected by external conditions. Fundamental propertyOf nuclei – spontaneous decay – Nobel Prize

Rutherford – Nature of radiations from radioactive substances – alpha, betaAnd gamma radiation – decay life time – radioactive series – Nobel Prize

All these radiations came from elements from the earth.

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Electroscopes – instruments which measure presence and amount of electric charge- indicated the presence of radiationWhich could change the charge on an electroscope

All electroscopes discharged with time even if they were shielded from all sides.

This indicated presence of radiation in the atmosphere around us which was thought to come from earth.

Adventurous scientists took electroscopes to high altitudes and observed whether they discharged faster or slower than on theearth.

Father Thomas Wolfe – up the Eiffel tower to 900 ft – observed an initial decrease in Discharge rate. 1910, expected if radiation was from earth; but then it stoppedDecreasing – indicating presence of non-earth origin radiation – atmospheric radiation ?

INSTRUMENTS TO OBSERVE COSMIC RAYS

Victor Hess (1911- 1914), Austrian scientist took Ionization Chambers in balloonsUp to about 17,000 ft and observed

After an initial decrease in discharge rate, the discharge rate kept on increasing up to the Highest altitude he went to. The following pictures show Hess:

Typical Ionization Chambers used to detect cosmic radiation in the atmosphere

How does the cosmic ray intensity increase with altitude ?

In 1913-14 Victor Hess first studied this with ion chambers in a balloon – his results are shown in figure:

Radiation dose as a function of altitude. Note the logarithmic scale On the x axis.

Altitude dependence of radiation established extraterrestrial origin of cosmic rays.

Latitude dependence of radiation, measured by taking ion chambers on expeditionsAround the earth – in the 20s and 30s and early 40s , established :

1. Cosmic radiation consists of charged particles

2. Most of these charged particles are positively charged and

3. They are mostly protons 0r nuclei of hydrogen atoms.

Magnetic Field direction

Positively charged cosmicray.

Coming out of the paper

A negatively charged particle would be deflected into the paper

Cosmic ray trajectories in the Eartrh's magnetic field

How cosmic rays get trapped in earth's magnetic field : Low energy cosmic rays(protons and electrons) spiral along magnetic field lines and bounce back and Forth forming radiation belts which have a lot of radiation. Shown in next slide.

Magentic Field of the Earth and trapping of Cosmic rays inVan-Allen belts.

CREAM instrument

Six many day Antarctic flights.

University of Chicago TRACER experiment to measureNuclei with Z > 3 (Lithium) in Balloons: Antarctic flights.

Flight instrument

Payload lifted by Balloon

At altitude – 130,000 ft The balloon expands toSize of two football fields.

GUMPHS detector

Indirect experiments based on terra firma

Use of the atmosphere to increase the area ofA single very high energy cosmic ray particle.

Develop a shower of fast particles moving withThe speed of light which is spread out over More than 50,000 square meters.

What cosmic rays do whenPropagating through theAtmosphere.

Produce:

PionsNucleonsMuonsGammasElectronsneutrinos

Cosmic rayCosmic ray

Air shower detector to observe cosmic rays with TeV to 100 PeV energies

The Tibet and ARGO air shower array in YanBajingThe Tibet and ARGO air shower array in YanBajing

Altitude 4,200 meters (about 15,000 ft)

AUGER Array in Argentina : World's largest cosmic ray detector !

What we know about cosmic rays of all energies now :What we know about cosmic rays of all energies now :