☄️ Cosmic Ray Air Showers

About this simulation

When a high-energy cosmic ray — usually a proton or a heavier atomic nucleus — slams into the top of the atmosphere at nearly the speed of light, it collides with an air nucleus and shatters into a spray of secondary particles. Each secondary can itself interact or decay, producing more particles, which produce more again — an extensive air shower that can spread over an area of many square kilometres by the time it reaches the ground.

How it works

• Heitler cascade model — a simple toy model where each generation of particles roughly doubles in number while each one carries half the energy of its parent, until particle energy drops to a critical value (~86 MeV in air) and the cascade dies out.
• Shower maximum (X_max) — the atmospheric depth where particle count peaks. Higher primary energy means more generations are needed to reach the critical energy, so X_max occurs deeper (closer to the ground) — this is the elongation rate.
• Nucleus type — a proton starts a single cascade. A heavier nucleus like iron behaves, to good approximation, like A independent nucleons each carrying E₀/A — this "superposition" makes iron showers develop higher in the atmosphere (shallower X_max) with less shower-to-shower fluctuation than protons.
• Muon component — charged pions produced in hadronic collisions decay into muons, which barely interact and punch through to the ground largely unattenuated, unlike the electromagnetic (electron/photon) component that gets absorbed.

Controls

• Primary energy — log₁₀ of the primary particle's energy in eV, from 10¹⁵ (just above the "knee") to 10²⁰ eV (ultra-high-energy).
• Primary particle — switch between a proton, an iron nucleus, and a pure electromagnetic gamma-ray primary.
• Zenith angle — how far from straight down the shower arrives; inclined showers travel a longer slant path through the same vertical atmosphere.
• Highlight muon component — dims the electromagnetic cascade so the penetrating muon tracks stand out.
• ☄️ Launch new primary — regenerates the cascade with the same settings but new random fluctuations, just like real showers vary event to event.

Did you know?

Ground-based observatories like the Pierre Auger Observatory in Argentina use arrays of water-Cherenkov detectors spread over thousands of square kilometres to sample the particle "footprint" of a shower and reconstruct the energy and likely composition of cosmic rays whose sources are still one of astrophysics' open mysteries.