The gold-leaf electroscope has been widely used in the past to study ionizing radiation.

EO 2.5DESCRIBE the operation of an electroscope ionization chamber.

The gold-leaf electroscope has been widely used in the past to study ionizing radiation. The first measurement of the properties of ionizing radiation was accomplished with this instrument. A microscope containing a graduated scale in the eyepiece is used to observe the gold leaf.

The newest electroscope utilizes a quartz fiber and has many advantages over the gold-leaf type. It is portable, less dependent on position, much smaller in size, and more sensitive. The capacity of the quartz fiber electroscope is about 0.2 pico-farads, and its voltage sensitivity is about one volt per division on the scale. The sensitive element is a fine gold plated quartz fiber mounted on a parallel metal support. Figure 22 illustrates a quartz fiber electroscope.

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Figure 22 Quartz Fiber Electroscope

A small piece of quartz fiber is mounted across the end of the gold-plated quartz fiber and serves as an index that is viewed through a microscope equipped with an eyepiece scale. The quartz fiber is charged by a battery pressing the charging key. As the quartz fiber is being charged, it is deflected from the support. It takes approximately 200 volts to produce full-scale deflection of the fiber. A glass window at the end of the ionization chamber allows for exposure of the fiber. As the gas (air) is ionized by the incident radiation, the fiber moves toward the position of zero charge. Due to the electroscope's dependability, simplicity, accuracy, and sensitivity, it is widely used in gamma radiation measurement.

A self-reading pocket dosimeter is an example of an electroscope ionization chamber. Pocket dosimeters provide personnel with a means of monitoring their radiation exposure. The dosimeters are available in many ranges of gamma exposures from 0 through 200 milliroentgens to 0 through 1000 roentgens. The sensitivity of the instrument is determined at the time of manufacture. Appropriate scale markings are provided with each dose range.

Summary

The operation of an electroscope ionization chamber is summarized below.

Electroscope Ionization Chamber Summary

The electroscope ionization chamber is charged using a battery.

Charging causes the quartz fiber to be deflected from the support.

When radiation ionizes the gas (air) in the chamber, the charge is reduced, and the fiber moves towards the zero charge position.