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.
