Composition of cosmic rays

The composition of cosmic rays can be divided into  

• Primary cosmic rays (before interacting with Earth's atmosphere) and
  
• Secondary cosmic rays (produced during interactions with Earth's atmosphere). 
  

Image source: https://www.facebook.com/cosmicparticles/

 

Here's a detailed breakdown:

1. Primary Cosmic Rays

Primary cosmic rays originate from outside Earth's atmosphere and consist mainly of high-energy particles. Their composition includes:

a. Atomic Nuclei (99% of primary cosmic rays):

• Protons (Hydrogen nuclei):
  ~90% of primary cosmic rays are protons.
• Alpha Particles (Helium nuclei):
  ~9% are alpha particles
• Heavier Nuclei:
  ~1% are heavier atomic nuclei, such as:
  • Carbon (C)
  • Oxygen (O)
  • Iron (Fe)
    These heavier elements are thought to originate from supernovae and other astrophysical sources.

b. Electrons (and Positrons):

• A small fraction (~1%) consists of high-energy electrons.
• Positrons, the antimatter counterpart of electrons, are also detected in smaller quantities.

c. High-Energy Gamma Rays:

• Some cosmic rays include gamma rays, which are high-energy photons.

d. Rare Components:

• Antiprotons: These antimatter particles are rare but detected in cosmic rays.
• Antinuclei: Extremely rare (e.g., antihelium), their detection could reveal insights into antimatter in the universe.

2. Secondary Cosmic Rays

Secondary cosmic rays are created when primary cosmic rays collide with atomic nuclei in Earth's atmosphere, leading to cascades of particles (air showers). The secondary particles include:

a. Muons ($\mu^\pm$):

• Highly penetrating particles created from the decay of pions ($\pi^\pm$) and kaons ($K^\pm$).
• Most secondary cosmic rays reaching the Earth's surface are muons.

b. Neutrinos ($\nu$):

• Produced during pion and muon decays.
• Neutrinos interact very weakly, allowing them to pass through matter almost undetected.

c. Pions ($\pi^\pm, \pi^0$):

• Short-lived particles produced during high-energy collisions.
• Charged pions decay into muons and neutrinos.
• Neutral pions ($\pi^0$) decay into gamma rays.

d. Gamma Rays ($\gamma$):

• High-energy photons produced by neutral pion decay.
• These gamma rays contribute to atmospheric ionization.

e. Electrons and Positrons:

• Generated in cascades, especially from gamma rays via pair production ($\gamma \to e^{-}$).

f. Other Particles:

• Neutrons: Produced during collisions, but they decay quickly into protons.
• Heavy Fragment Nuclei: Secondary nuclei formed through spallation reactions, where primary nuclei are broken apart.

Reference

All are included in the text as hyperlink

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