Cosmic Rays

A spark chamber can be used to detect cosmic rays. Cosmic rays are high energy charged particles which typically have energies ranging between 106 - 1020 eV (10-13 - 10 J). (10J is sufficient energy to heat a kilogram of water by 0.007 0C.) Although in these terms this does not sound a very large amount of energy, when one considers the size of the cosmic rays, (typically 10-29kg and of the order 10-18m in radius) it can be appreciated that this is a large energy for each of these minute particles to have.

Cosmic rays originate in outer space, (mainly from supernova explosions but also from stars - click here to see where cosmic rays come from) travel at the speed of light and strike the Earth from all directions.

The cosmic rays strike the Earth's surface at the rate of about 1 cosmic ray every square centimetre every minute. Perhaps a more meaningful way to look at this is that during an average nights sleep a person will have on average of the order a million cosmic rays travelling through their body!

Cosmic rays are very penetrating and as well as penetrating through the atmosphere they have also been detected under the ground such as in the London Underground system as well as down deep mines. The following table gives some comparison of penetration for different types of radiation. So that of cosmic rays can be compared.

Table 1: Comparing typical properties of a variety of types of radiation

Radiation Mass Electric Charge Average Penetration Depth in Air Summary
X-rays 0 0 100m Very energetic form of light
Alpha rays 3.7GeV +2e 0.1m Equivalent structure to He nucleus
Gamma rays 0 0 1km Very energetic form of light
Primary cosmic rays Mixed Mixed approx. 10km Mostly Hydrogen and Helium nuclei
Secondary cosmic rays Mixed Mixed approx. 10km Mostly muons

Cosmic rays are a useful tool in many aspects of science

(A) The large energies of cosmic rays allow them to be used to smash up atoms from which more can be learnt about the atom and the structure of matter all around us

(B) The source of cosmic rays are of interest to astronomers and cosmologists (see the University of Birmingham Astrophysics web page: )

(C) Radiocarbon dating resulted from cosmic ray research (see )

Particle physicists are really only interested in aspect (A)

Are cosmic rays harmful?

What does a Spark Chamber Detect?

Where do primary cosmic rays originate?

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