1. Cosmic Rays Overview

2. The top of the Earth’s Atmosphere is bombarded with particles
1) From the sun. Solar wind, Coronal Ejection. Heavily attenuated by a few mm of aluminum.
2) True “Cosmic” Rays. These apparently come from outside the solar system and from all directions -isotropic- mostly protons.
Energies range from a few GeV to 10^13 GeV, ie from a micro-micro Joule to 10 J. The ultra-high energy ones bring a lot of energy but are rare. Total energy is about the same as starlight.
Highest energies, one per square meter/century

4. At mountain altitudes there are still remains of some of the showers, but at sea level most of the hadronic (strongly interacting) part has died out and the flux is almost entirely (95%) muons. The 5% is a few surviving hadrons and electrons from “hard” hits of muons on the electrons (knock-on electrons).

5. Not hit a nucleus is dotted line

8. The nucleus is an incredibly small part of the volume and the rest of the volume is filled with the orbits of the electrons.
All charged particles lose a little energy going through the electron swarm – like friction.
Hadons interact if they hit a nucleus.
Muons go right through a nucleus so electron friction is all they feel as they go through matter.
Friction is understood so range determines energy for each and thus energy spectrum.

10. When we put our four counters on a square a few meters across and run in shower mode (2-fold or higher coincidence), we get coincidences from:
1) The dying remains of a big hadronic shower – protons and pions.
2) Muons from pion decay from showers high in the atmosphere.

11. At high energies reaction products are thrown very forward, within a few degrees of the direction of the incident particle.
A shower which starts at the top of the atmosphere (up 30 km) has spread to a radius of only a few kilometers at sea level.
Finding simultaneous showers in schools a few km apart is one way to use our units to look for very high energy showers!
Bob will show you how to do it.
Brenda found a clever way to get beginning students actively involved in understanding showers.