The characteristics of some of the more commonly used detectors are summarized below. Ionization chambers measure dose and dose rate from gamma and x-radiations. A typical ionization chamber that measures total dose is the pocket dosimeter. It is the size of a large fountain pen. It has a chamber containing two electrodes, one of which is a quartz fiber loop free to move with respect to its mounting.
Radiation entering the chamber causes ionization within the sensitive volume.
The distance the fiber moves is proportional to the dose received in the chamber. Instruments of this type are sensitive to severe shock and humidity and small enough to be worn comfortably. The great advantage of this type of instrument illustrated, is that it can be read at any time without the aid of a supplementary charger-reader by simply holding it up to a source of light and looking into it. Geiger-Mueller counters are normally used for detecting single ionizing events which take place within the sensitive volume of the counter. They are very rugged and sensitive to low levels of radiation.