Cloud chamber – radioactivity in a cosmic setting

Brief description:

Cloud chambers are boxes specially made to detect charged particles and radiation. In this activity, a cloud chamber is used to observe alpha and beta particles, the charged products of the radioactive decay of thorium-232.

Students should already have been introduced to the concept of radioactive decay and the differences between alpha and beta radiation.

This experiment will assist students in their understanding by providing a physical demonstration of radioactive decay.

Students will observe the condensation trails that charged particles leave in their wake in a cloud chamber, and learn to identify particles based on the trail properties. Trails made by cosmic rays can be seen in the cloud chamber, which could provide a starting point for introducing cosmic rays and their deflection by the Earth’s magnetic field.

Students will practice calculating and writing radioactive decay equations. Implications of radiation for ESA are discussed, including the negative effects of radiation on circuits, and the use of radioactive decay as a power source.

Subject: Science, Chemistry, Physics
Learning Objectives:

  • Learn about fundamental particles and how they interact, including the interactions between charged particles and magnetic fields
  • Define atomic number and mass number
  • Discover radiation and radioactive decay, and how it can be used as a power source for spacecraft
  • Investigate the negative effects of ionising radiation on electronics
  • learn about cosmic rays including their interactions with the atmosphere
  • Improve general experimental skills including using equipment appropriately and making and recording observations.
  • Communicate and discuss results, ask relevant questions to expand understanding and knowledge of a subject.
  • Apply knowledge gained through experimental observations to solve theoretical problems.

Age range:
14 – 18 years old

Preparation: 5 minutes per cloud chamber
Lesson: 1 hour

Resource available in:
English, French, and Italian.
Activity 1: Building a cloud chamber

In this hands-on experiment, students will build their very own cloud chamber, allowing them to observe the radioactive decay of thorium-232, a radioactive thorium isotope.

Alpha and beta emission can be observed in the form of condensation trails (contrails) in the alcohol vapour inside the chamber, allowing us to better unders

To prepare in advance:
  • Medium-sized plastic fish tank
  • Adhesive-backed felt (or normal felt and glue appropriate for felt and plastic)

To perform the experiment:
  • Two thoriated tungsten welding rods (or other alpha/beta source)
  • About 2.5 kg dry ice (solid CO2)
  • 20 ml isopropyl alcohol, also known as isopropanol (or ethanol if this is unavailable)
  • A plastic fish tank with pre-attached felt
  • Two metal trays (baking trays work well)
  • One piece of black card or laminated black paper (to line trays if they are not dark)
  • One or two intense light sources (e.g. an LED light strip, torch, or slide projector light)
  • A sheet of paper to wrap around one rod
  • Poster putty or reusable adhesive
  • A pipette
  • Thermal protective gloves
  • Safety glasses (one pair per person)
Activity 2: Test your knowledge of radioactive decay

In this activity, students will discuss the topics explored in the experimental stage, and complete activities to test their knowledge.

  • Student worksheet printed for each student
  • Pen/pencil

Did you know?

On Earth we are protected from charged cosmic rays by a magnetic field, the magnetosphere, which is generated by the motion of magnetic elements in the Earth’s core. The magnetic field extends almost twice the distance of the Moon but the further from the Earth, the weaker it is and so there is less protection from ionising space particles.

The NASA/ESA/ASI Cassini Huygens mission to Saturn had to cope with this cosmic radiation as it ventured far beyond the edge of the magnetosphere. Once Cassini-Huygens reached its destination, it was protected by Saturn’s own powerful magnetic field.

Cassini-Huygens at Saturn