Spark image

The spark counter

This consists of a fine metal gauze mounted about a millimetre away from a thin wire (Figure 1). A voltage is applied between the two so that sparking takes place between them - this usually requires some 4000 - 5000 V. The voltage is then reduced until sparking just stops.

If an alpha-source is brought up close to the gauze it will ionise the air, and sparks will occur between the gauze and wire. With beta and gamma sources insufficient ions are usually produced for sparking to take place. The spark counter can be used to measure the range of alpha-particles, and in nuclear research a stack of spark counters is used to show the track of a particle as a line of sparks.


schoolphysics: Spark counter animation

To see an animation of a spark counter click on the animation link.

© Keith Gibbs 2011