They are now largely superseded by electronic personal dosimeters for short term monitoring. Geiger tube dosimeter These use a conventional Geiger-Muller tube typically a ZP1301 or similar energy compensated tube requiring between 600 and 700V and pulse detection components. The display on most was a bubble or miniature LCD type with 4 digits and a discrete counter IC such as 74C925/6, LED units usually have a button to enable the display for long battery life and an infrared emitter for count verification and calibration. The voltage is derived from a separate pinned or wire-ended module that often uses a unijunction transistor driving a small step-up coil and multiplier stage which though expensive is reliable over time and especially in high radiation environments sharing this trait with tunnel diodes though the encapsulants, inductors and capacitors have been known to break down internally over time. These have the disadvantage that the stored becquerel or microsievert count is volatile and vanishes if the power supply gets disconnected though there can be a low leakage capacitor to prevent short term battery disconnection from impact disrupting the memory. The fix is to use a long life battery, knurled high quality contacts and security screws to hold the typically glass front panel in place, though more recent units log counts versus time to a high capacity non-volatile memory such as 24C256 so it can be read out via a serial port. Dosimetry dose quantities The operational quantity for personal dosimetry is the personal dose equivalent, which is defined by the International Commission on Radiological Protection as the dose equivalent in soft tissue at an appropriate depth, below a specified point on the human body. The specified point is usually given by the position where the individual’s dosimeter is worn. Instrument and dosimeter response This is an actual reading obtained from such as an ambient dose gamma monitor, or a personal dosimeter. The dosimeter is calibrated in a known radiation field to ensure display of accurate operational quantities and allow a relationship to known health effect. The personal dose equivalent is used to assess dose uptake, and allow regulatory limits to be met. It is the figure usually entered into the records of external dose for occupational radiation workers. The dosimeter plays an important role within the international radiation protection system developed by the International Commission on Radiological Protection and the International Commission on Radiation Units and