Cosmic rays Flashcards
When did cosmic rays start ennoying scientist?
Beggining of the 20th century => unexplained dark current
Who suggested that CR might come from radioactivity
Rutherford
What did Wulf do to explain CR’s origin ?
He conducted an experiment on the top of the Eiffel tower and observed a decrease of the “dark current” by a factor of 2. He concluded that it was originated by the Earth
What was Heiss contribution to CR?
He discovered on a balloon flight that ionizing radiation is coming into Earth atmosphere at 5km altitude from above (Nobel Prize 1936)
Who confirmed the particule nature of the CR?
Millikan and Compton => they coined the name cosmic ray
Cosmic ray : a remarkable power law between … and … ?
10^10 to 10^15 eV
But steepens at the “knee” at 10^16 and recovers at the “ankle” at 10^19
What clue do we have to determine CR’s origin ?
Its componant abundance
=> which is very similar to the Sun
What difference do we observe between the CR and the Sun’s abundance?
Li, B and Be are more abundant in the CR => they are secondary nucleii formed in the spallation of heavier elements
Mn, V, Sc are more abundant in the CR => they come from the fragmentation of Fe
What is the rigidity?
It is a quantity that measures the deflection of a particle of charge Z and momentum p in a magnetic field B
Particles with different charge and masses have the same dynamics in a magnetic field if they have the same rigidity.
What is the mathematical expression of the rigidity?
R = energy/electric charge = pc / Ze
How do we compute the maximal energy reached by protons composing cosmic rays and slown down by the CMB ?
We use the conservation of the 4-momentum => GZK cut-off
What is the limit set by the GZK cutoff?
5.10^19 eV
What is the UHECR vs GZK cutoff paradox ?
G, Z and K predicted a suppression of cosmic ray flux above 5.10^19eV. But cosmic rays up to 3.10^20eV have been observed (Ultrza High Energetic Cosmic Rays). How are they produced and where do they come from?
Comment détermine-t-on l’origine des rayonnements cosmiques ?
On utilise le rayon de Larmor pour déterminer l’origine des rayonnements cosmiques en fonction de leur énergie.
En comparant le rayon de Larmor à la taille caractéristique du champ magnétique B on détermine si la particule à confinée par ce champ ou si elle relativement indépendante.
On obtient une limite au delà de laquelle le champ B de taille L ne peut expliquer l’accélération d’une particule.
D’où viennent les CR les + énergétiques?
Ils sont d’origine extra-galactique.
