Gallery 3

Cloud Chamber

Photo showing cosmic rays as vapour trails passing through Cloud Chamber exhibit

How it works

Watch closely as tiny vapour trails move across the Cloud Chamber

Things to try or ask around the exhibit

  • Watch closely for wispy lines or vapour trails moving across the Cloud Chamber.
  • What could cause these vapour trails to form? Are vapour trails affected by where you stand around the Cloud Chamber?
  • Why are the vapour trails different in length and thickness?
  • What is the most common type of vapour trail?
  • What is the rarest type of vapour trail?


Natural cosmic radiation from space (particularly exploding stars called supernovas) is constantly reaching us on Earth but we are typically unaware of these high energy particles. The particles enter Earth’s atmosphere and crash into air molecules to form more high energy particles (a bit like a domino effect at a sub-atomic scale). A single ‘primary’ particle from outer space creates a shower of ‘secondary’ particles within the atmosphere.

When you watch vapour trails inside the Cloud Chamber, most are caused by ‘secondary’ particles called electrons and muons (which have a negative charge like electrons but they are 207 times heavier). Occasionally, you may see heavier vapour trails inside the Cloud Chamber and these are usually caused by heavier protons generated by natural radioactivity in the air or by the exhibit itself.

The Cloud Chamber is filled with vaporised alcohol. When different types of radiation enter the chamber, they electrically charge (ionise) the vapour to create the trails that you see as the wispy lines and dots.

Cloud Chambers were invented in 1911 to study high-energy particles, although we study these high energy particles today using electronic devices.  

Finding the science in your world

Background radiation is a natural part of our environment and all objects emit tiny trace amounts of radiation.

Exposure to radiation can be measured using a unit called milliSieverts (mSv).

In Australia, a person at sea level is exposed to cosmic radiation of about 0.36 mSv per year. If you travel high in the atmosphere (as an airline pilot or passenger), you are exposed to higher levels of radiation. Over the course of a year, an airline pilot is exposed to 2-6 mSv of radiation. In comparison, a typical chest X-Ray exposes a person to around 0.02 mSv.